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NTU ASTROnomical society
exoplanets astrophotogra spa gravitat structure of u
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EXOPLANETS
The Search For Habitable Exoplanets
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ARE WE THE ONLY ONE? Daniel (NTUAS)
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EXOPLANETS
WHAT ARE
EXOPLANETS? W
e might not realize it, but the universe is larger than it seems. When we go out in the dark and look up to the sky, we can see many stars ‘hanging’ on the sky (well, maybe quite rare in Singapore), and all of them seem relatively near to us. We might as well expect that the size of the universe is just up to the distance between us and those beautiful stars. However, from thousands of observations and researches, astronomers have found more stars, millions of them, which cannot be seen by our naked eyes, and most of them are very far away from us, millions, even billions, of light years away. From all these stars, there are chances that planets like Earth orbit around them. In fact, about 1 in 5 Sun-like stars have an Earth-sized planet. These planets are called extrasolar planets (planets that are outside the Solar System), or commonly abbreviated as exoplanets.
The youngest exoplanet yet discovered is less than 1 million years old and orbits Coku Tau 4, a star 420 light-years away. Image Credit: NASA
the only star system in the universe, and there are chances that habitable planets like Earth might exist. However, up to this time, astronomers are still struggling to find any forms of life outside the Earth, although there are some exoplanets that have been classified as ‘planets orbiting in habitable zone’. Like all the planets in our own Solar System, exoplanets may exist as either rocky (terrestrial) planets or gaseous (Jovian) planets, or even icy planets, and all of them come in huge variety of sizes and orbits.
This fact has proved that we are not
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WHY
SEARCH
An artist’s concept of the planets orbiting Pulsar PSR B1257+12 Image Credit: wikipedia.org
F
or centuries, scientists and astronomers had speculated that exoplanets might exist, but there was no way of detecting or of knowing their frequency or how similar they might be to the planets in our own Solar System. In the 19th century there were various claims regarding the discoveries of exoplanets, all of which were rejected by astronomers. However, in 1992, the first detection of exoplanet was confirmed with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. As of 1 September 2016, a total of 3518 confirmed exoplanets are listed in the Extrasolar Planets Encyclopaedia. Some of you might ask, ‘Why are they searching for exoplanets?’, ‘What is the point in studying them?’. Well, there are some reasons why astronomers are very eager in searching and learning exoplanets. The first reason
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FOR EXOPLANETS? is that exoplanets, especially those in younger star systems, will provide astronomers on how planets are formed in their early stages, and that would result in better understanding on how our Solar System formed nearly 5 billion years ago. Another reason is that while searching for exoplanets, astronomers are hopeful that they might encounter a planet that is in the habitable zone, which may give clues to astronomers about other life forms outside Earth, allowing us to be one step closer to discovering extraterrestrial life.
EXOPLANETS
HOW DO ASTRONOMERS SEARCH FOR EXOPLANETS? Now, here comes the big question: How exactly do astronomers discover and identify exoplanets? Now, here comes the big question: How exactly do astronomers discover and identify exoplanets? Exoplanets are very difficult to see from Earth, so the most effective way is to use indirect methods to identify them. There are three most common and simple approaches that astronomers can use to discover and identify the characteristics of exoplanets: the radial velocity method (Doppler Spectroscopy Method), transit photometry method, and direct imaging of exoplanets.
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Stellar Wobble due to the gravity of planet(s) orbiting around the star. Image Credit: nasa.gov
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Radial Velocity Method (Doppler Spectroscopy Method) When a star has planet(s) orbiting around it, the star will also orbit around the center of mass of the system, creating a ‘wobbling’ effect. This leads to the variation of the speed of the star moving towards or away from the Earth, i.e. the variation in radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement of the star’s spectral lines due to the Doppler’s Effect. Blueshift will be detected if the star is moving towards the Earth. Likewise, redshift will be detected if the star is moving away from the Earth. From the data obtained by using this method, characteristics of the planet like the eccentricity of its orbit and its minimum mass can be identified.
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EXOPLANETS
From the light curve above, and also the average orbital speed (from Doppler’s Effect Method) of the planet, the radius of the planet can be determined. Hence, the density of the planet can also be determined. Image Credit: hao.ucar.edu
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Transit Photometry Method A transit is an astronomical event when at least one celestial body appears to move across the face of another celestial body, in this case the exoplanet(s) appears moving across the parent star’s disk, hence hiding a small part of it, as seen by an observer at some particular vantage point. When an exoplanet transits in front of its parent star, the observed visual brightness of the star will decrease by a certain amount. This drop in brightness can be used to determine various characteristics of the exoplanet: the size of the planet (hence the density of the planet when mass of planet is known) and its atmosphere. Moreover, the elements present in the atmosphere of the planet can also be determined. These three features are very important as they help astronomers to determine whether the conditions on the planet are suitable to support life.
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Direct image of exoplanets around the star HR8799 using a Vortex coronagraphs (a method in which the light from the star is blocked, leaving the planet visible) Image Credit: Wikimedia.org
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Direct Imaging of Exoplanets Planets are extremely faint light sources compared to stars, hence the light from these planets tends to be lost in the glare of their parent star. It is quite hard to detect and resolve them directly from their host star, so planets are often detected through their thermal emission instead, which is obtain from imaging the planet directly, mostly using space-based telescope. Direct imaging can give a rough estimate of the planet’s mass, which is derived from its temperature. In general, the cooler the planet, the less massive it is. In some cases, the radius of the planet can also be determined when the planet’s temperature, its apparent brightness and the distance from Earth is known. This method can also be used to measure the orbit of the planet around the star accurately.
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EXOPLANETS
CRITERIA OF HABITABLE EXOPLANETS Essentially, a planet must be in the so-called habitable zone in order to support life in it. The habitable zone is the belt around a star where temperatures are ideal for liquid water – an essential ingredient for life – to exist on a planet’s surface. Beyond this zone, temperatures may be too cold. Between the star and this zone, temperatures may be too hot. Both conditions are not suitable for life. To determine the habitable zone of a star, astronomers first determine the stellar properties of the star, for example the amount of radiation it emits. If a star emits more radiation, its habitable zone will be further out, and vice versa.
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Composition of the planet The main assumption about habitable planets is that they are terrestrial, which are primarily made up of silicate rocks. Such planets are more preferred as it is assumed that there will be surfaces where life could habor, while it is not ruled out that life could evolve in the clouds of giant gaseous planets (although it is very unlikely).
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Mass Generally, less massive planet are unlikely able to ‘capture’ gaseous molecules (O2, N2, etc.) to form layers of atmosphere due to their weak gravity. Hence, more massive planets with suitable atmospheric conditions (not to much greenhouse gases) are more preferred.
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Orbit and Rotation of the planet Planets with low orbit eccentricity is more preferred as high eccentricity orbit may cause fluctuations in temperature on its surface, which may create harsh conditions for lifeforms to evolve. Planet’s rotational axis must also meet certain criteria, such as little or no axial tilt. Little or no axial tilt means that the planet has moderate seasons, which is a good condition for life to evolve.
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Environmental Condition of the planet Astronomers must ensure that the overall condition on the planet is suitable for life: All the four essential elements for life – oxygen, nitrogen, carbon, and hydrogen should exist, temperature on the planet should not be to extreme, water available in liquid form, suitable atmospheric conditions to protect life on the planet (such as the ozone layer on Earth), and also the geochemistry of the planet to support life.
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SO ARE WE STILL ALONE?
Well, yes, we are (currently). So far, Earth is the only known planet to harbor life. In early human history, people thought that the Earth was the center of solar system, of the universe, and that every celestial object orbited the Earth. Hence, it is no surprise that there was no concept of extraterrestrial life back then. It was only until the early modern period that people realize that Earth is a planet orbiting the Sun – it has no special position in the universe, that people begin to imagine life outside Earth. Up to now, astronomers have found thousands of exoplanets and yet, still no sign of extraterrestrial life. However, astronomers have found and observed many exoplanets that are possibly habitable, so perhaps it is a matter of time before we can introduce ourselves to aliens, or perhaps we can colonize other (exo)planets, so let’s hope that those people in NASA and other space agencies do their best to solve this one (among the biggest mysteries in the world).
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ASTROPHOTO
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You are no idiot of course. Astrophotography is a form of photography that captures celestial objects and occurrences. Much like other forms of photography, it requires a very specific set up and special equipment that helps to maximize the amount of light that can be collected from stars many light-years away. With the commercialization of digital photography, it is now also possible to process your image for a pleasing effect that film cannot replicate. There are also three types of astrophotography: wide-field, deep-sky, and planetary imaging. Wide-field images capture the entire sky: the Milky Way Galaxy is one such highlight. DeepSky imaging captures nebulae, star clusters and galaxies, and planetary imaging captures planets in great detail. Each has their own specific challenges unique to the techniques and equipment used to obtain the image. The common consensus is that astrophotography is a very expensive hobby that few can afford, and only the most patient of astronomers dabble in this very niche hobby. However, times of film and manually guided telescopes are way past, and with the advent of digital cameras and smart-guided mounts for more affordable prices, astrophotography today is a much less money-intensive hobby and well in reach of students like me (yes, but it still burns a big hole in my wallet!) For instance, a very decent DSLR from Nikon or Canon can cost about $1000, a decent telescope optical tube assembly costs $500 if you buy secondhand, a beginner computerized mount costs $1200 and the ASTRONICLE 2017
accessories such as the guide camera and guide scope cost another $600 or so. Yes, it does not cost an arm and a leg and a kidney! This article will concentrate on the basics of astrophotography: the equipment and software used and the specifications they hold, as well as the characteristics they have. I will be briefly going through all the parts and I will also give a few equipment recommendations should anyone want to indulge in this expensive yet satisfying hobby.
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THE CAMERA [COMPULSORY]
+ LENSES
[ OPTIONAL FOR DEEP SKY AND PLANETARY ]
Of course you need one of these to start astrophotography! The digital camera is the go-to for modern imaging, unless you would like to torture yourself in excruciating pain using film cameras without the preview function. Digital cameras register photons (light particles) that fall onto the sensor. The sensor is split into millions of pixels. Each pixel absorbs photons and translates it into an electrical current that shows a dot on the screen. As more photons get absorbed, the particular pixel will display a brighter dot on the final image. After an exposure, the millions of pixels that are composed of a gradient of bright and dark dots generate the image. There are three settings on a camera, regardless of brand or type: ISO, aperture and shutter speed. ISO (International Standard of Operation) dictates the sensitivity of the sensor chip. The higher the ISO, the more
sensitive the chip is to light, but also the more susceptible to thermal noise (which causes the image to be noisier and look pixilated). Generally, an ISO between 100 and 6400 is used, where 6400 and above are reserved for cameras that are able to handle higher ISOs (e.g. Sony A7S). For the film era, the ISO of the film is how sensitive the film is to light. Aperture determines the “fastness� of the lens. This is the focal length of the lens divided by the width of the lens. A fast lens (f/1.4 or so) requires a shorter shutter speed as it allows more light to go through, and also meant a smaller magnification. This also means that the hole that allows light in is bigger, thus resulting in a brighter image. A slow lens (f/10 plus) trades off the fast shutter speed for higher magnification and has a smaller hole to allow less light to pass ASTRONICLE 2017
through, thus a vice versa of the fast lens. For every full stop you increase, you have to double your exposure time (please read up! The full f-stop should look like this: 1.0, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32). However, for telescope OTAs (optical tube assembly), the aperture should remain the same for the particular telescope that is used, thus this section is less relevant. Shutter speed determines the amount of time the shutter remains open, which also dictates the amount of light that is captured by the sensor. A slower shutter speed results in a longer the exposure and thus, a brighter image. Typically, about 20s of shutter speed and ISO 6400 with an f/4 lens should produce a very decent shot of our Milky Way. For more advanced astrophotographers doing deep sky imaging, the goto cameras are CCDs cooled to below -5 degrees Celsius for best reduction of thermal noise and plugged straight into a computer for viewing. Planetary imagers will tend to use smaller video cameras and take short videos of planets, then stacking all the images for the best possible details to be seen, such as the rings of Saturn and the belts of Jupiter. For most beginners, the regular DSLRs are attached to the main telescope body via a T-ring specific to the camera body and a T-adaptor for connecting to the telescope. During imaging, remote shutter release is recommended to prevent the setup from wobbling and stabilizing.
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Where the ISO, aperture and exposure are typically located on your camera. Image Credit: https://pixabay.com/en/camera-canon-photography-dslr-1702015/
RECOMMENDED
DSLR / MIRRORLESS
CAMERA BODIES
TinyMOS Tiny1 Best value you can get for a beginner astrocam! Sony A7S Canon 760D Nikon D7200
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E S S A E B U T L A C I THE OPT The telescope OTA is the next important piece of equipment for the planetary and deep-sky imagers. The telescope has two functions: to concentrate light collected from the “light bucket� into a small focal point to increase intensity of light, and to magnify the image as well. Telescopes are labeled by their aperture, which is the diameter of its optics, the focal length of the telescope, and the f-number not unlike camera lenses. Three basic designs of telescopes are made: refractors, reflectors and catadioptric types. Each has its own advantages and disadvantages and is used for different situations.
most popular for deep sky imagers for their clarity and ease of maintenance. Small triplet apochromatic refractors of 70-100mm aperture with f-number (aka relative aperture, f-stop, focal ratio) between f/5.5 to f/7 are most commonly used for general imagery of nebulae, galaxies and other relatively wide-angled images. As apochromatic refractors use high-quality glass that is expensive to produce, larger (>>127mm) refractors would increase in cost exponentially and the sale of your kidneys is recommended if you want to purchase one (please, don’t).
The refractor uses lenses to refract light into a single focus and is the
The reflector uses curved mirrors to reflect light into a single focus and is most effective for larger apertures ASTRONICLE 2017
Some Recommended Beginner OTAs:
Some Recommended beginner OTAs:
Sky Watcher/Explore Scientific/Sharpstar/Sky Rover 80ED Apochromatic Refractors Basically any 80mm apo is a good start Vixen ED81SII Apochromatic Refractor (apo doublet) Sky Watcher N150 Newtonian Reflector GSO 6” Ritchey-Chrétien Celestron C5/C6 Schmitt-Cassegrain Sky Watcher BK127 5” Maksutov-Cassegrain Takahashi FSQ85 refractor If you feel rich and have money to throw around
EMBLY
!! Y D O B E P O C S LE E T E H T , S D R IN OTHER WO
where the cost of the aforementioned refractors reach astronomical levels (pun intended) when built of the same aperture. Indeed, the world’s largest telescopes are reflectors, even the Hubble space telescope! There are a few types of reflectors, notably the Newtonian, the Cassegrain and the Ritchey-Chrétien. The Newtonian is known for large apertures and fast focal ratios of around f/4, resulting in wide fields of view and shorter shutter speeds. The Cassegrain and the Ritchey-Chrétien have slower focal ratios and is used for general imagery of objects that requires higher magnification. However, reflectors
out of alignment requires the mirrors to be collimated every now and then. The catadioptric telescopes use a combination of lenses and mirrors to get the best of both worlds. These telescopes are compact and well protected from the elements, making them popular travelling scopes. They cost a bit more than the reflector but still less than a refractor of the same aperture. Examples are the Schmitt-Cassegrain, Maksutov-Cassegrain and the Maksutov-Newtonian. These telescopes (there is an exception. See Ricardi Honders Astrograph) have a rather slow focal ratio and are best for
suffer from an open mirror that attracts dust and elements, and the possibility of the mirrors being knocked
smaller objects or planets, which require much larger magnifications.
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ASTROPHOTO
THE
MOUNANTD TRIPOD You can’t be propping your setup on a rock!
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The telescope is only as good as the mount supporting it, so do not buy a 5-digit Takahashi refractor and mount it on that wobbly tripod that came free with your DSLR, please don’t! There are two types of mounts: the alt-azimuth mount (usually manual) and the equatorial mounts. Since the alt-azimuth mount is usually unable to do proper tracking without rotation of the image, only the heavy equatorial mount is usable for photography. If you are doing a simple shot of the Milky Way, a sturdy tripod will suffice. Only use that wobbly tripod if you have no other option. As the shutter speed is below 30 seconds, the movement of the sky is too small to be registered in the image and can be overlooked. Any longer exposures require some form of tracking such that the image won’t have any star trail (which is when stars leave a light trail on your long exposures because Earth is always rotating).
Tracking mounts use motors to compensate for the Earth’s rotational period. It also has 3 axles: one of them is aligned with the North Celestial Pole for Right Ascension (RA), one for adjusting the latitude you are on and the last for Declination (DEC). Most tracking mounts for telescopes are bulky and heavy, though there are some mini mounts for cameras that only weigh very little. Tracking mounts of today come with a computer inside that allows the user to find objects in the sky quickly (also known as go-to) and make adjustments as needed for smooth tracking – necessary for astrophotography. For the wide-angle specialist, they can also mount their cameras to piggyback on a telescope setup to make use of the tracking mounts as well to allow exposures of over 30 seconds.
Some Beginner Tracking Mounts To Consider (Singapore-use): Vixen Polarie For cameras only. iOptron CEM25P Center-Balanced Equatorial Mount Celestron AVX German Equatorial Mount Please Mod for low-latitude. ASTRONICLE 2017
Celestron CG-4 with Motor drive Non-computerized. Sky-Watcher AZ-EQ5 German Equatorial Mount
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E C C A E TH
Power Supply The Guiding System As our club president Winston has mentioned, the difference between NUS Astronomical Society and us is a guide scope and guide camera, as up to recently, our club cannot take long exposure images due to the lack of a guider. The guider system ensures that the object we are focusing on stays center of the image without drifting off. It uses the guide camera to capture an image through the guide scope, sends it to a computer, and the computer would tell the mount how much to compensate for the drifting. This allows the telescope to track an object for hours without losing it. The go-to software for guiding is PHD or PHD2 (Push Here Dummy), which is simple to use and provides a useful graph on how much the mount has compensated.
Ready to go? Not yet! How can you do astrophotography without power supply? For wide-field photography, you will only need batteries for your camera and probably that Vixen Polarie you probably picked up, but for the rest of us using telescopes and computerized mounts, a 12V DC power supply is a must if you plan to image from a remote site with no electricity. Here are some recommendations: Either pick up a few car batteries that can provide 12V and the correct current (anything with too much voltage can fry your mount!!) or buy Lithium-ion car-starters (the higher the capacity, the better!) to power up your rig. It should last about 4 hours or so and provide plenty of time to image the object you want. If you have access to a wall socket, please get a wire extension and extra sockets for direct power to your telescope and your computers!
Filters (Narrowband and Broadband) Astronomical filters come in both narrowband and broadband versions. These filters are very useful to filter out light pollution and only allowing very specific wavelengths of light to pass through. Narrowband filters get rid of most of the visible spectrum and only allow specific wavelengths to transmit. Best examples include H-alpha filter at 656.28nm and O-III filter at 495.9nm for imaging faint nebulae that emits strongly in those wavelengths. Broadband filters blocks out some wavelengths and allows most of the spectrum to transmit. An example is the Light-pollution reduction filters that blocks out the sodium and mercury light that is the light source for many conventional electrical lamps responsible for light pollution.
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S E I R O ESS
ITS TIME TO GIT GUD.
Computer Software As all we astrophotographers know, digital imaging is the new king (adieu film!) so computer software for processing and guiding is always a welcome addition to any astrophotographer. Here I will put down some free software for download to help you to start processing your images. As stated before, the deep-sky and planetary imagers will be using PHD or PHD2 guiding software for keeping the object locked in center. Planetary imagers would require a live stream for their videos to work, and thus a good software is oaCapture for Mac and Autostakkert2 for PC to get the job done. The latter software helps to stack planetary images for you as well! For Mac users, Lynkeos should help you to stack images for planets. For Deep-sky and wide-field users, Deep Sky Stacker is the default go-to software for stacking of images. If you have a good selection of images that are good quality, stacking them eliminates thermal noise and bad pixels. Follow the instructions online and get to work! As for processing of the images after they have been stacked, Adobe Lightroom or Photoshop with the Camera Raw attachment can be used to tweak the image to its final form.
Others: Flatteners (Refractors) Camera sensors are flat objects, and thus require the image to be flattened for the best effect. As refractors generate an image that is not flat, a flattener is needed so vignetting is much less obvious on the camera. Reducers (Refractors/ SCTs) Reducers are lenses that help to reduce the focal ratio of the telescope. This can help a normally slow telescope to be faster and more efficient for pictures, the trade-off being a lower magnification. These are used for refractors, Schmitt-Cassegrains, as well as Ritchey-Chrétien telescopes. Coma Correctors (Reflectors) Coma Correctors eliminate the coma effect at the edges of an image in a fast (f/4) Newtonian Reflector telescope, due to the parabolic shape of the mirror not being very good at producing sharp images at the edges.
All these items would attach snugly at the back of the telescope’s 2” socket provided if you had gone 2”. Otherwise, you use a 1.25” socket which slightly crops the image if you use a camera with a big sensor.
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ASTROPHOTO
Of course, you don’t do a lot of astrophotography in Singapore! Unfortunately, our sky is badly light-polluted and the effect can be seen even in Desaru! The best way to avoid light pollution is to get out of the city and go overseas to do your imaging, so you can at least see the Milky Way with your naked eyes. The other, more expensive solution is to purchase a set of broadband filters that sieve out light generated by streetlamps and homes or narrowband filters that only allow a narrow set of wavelengths to transmit. Some of the better places for stargazing in Malaysia include the outskirts of Mersing Town, Desaru, Malacca and so on. If staying at Singapore suits you better, be at a
Now with so many tools and information in your hands (which I presume is bigger than Donald Trump’s cocktail-sausage fingered ones), you can bring out that rusty old DSLR camera you probably left in your house and didn’t use for a long time and give it some new life in astrophotography, or you can just continue and enjoy all the images that our fellow astrophotographers churn out every now and then. I shall see myself out then, happily playing with my new toys (and yes they hurt my wallet till today!) Clear Skies ahead!! Zong Yang Resident Astrophotographer of NTUAS
dark field with less light pollution (for instance, NTU SRC field) to give astrophotography a shot! Other friendly astronomers are also in reach at the Singapore Science Center every Friday evening unless stated so.
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Check out these awe some photos taken by our NTUAS Astrophotogra phers! ut astrophotography, If you would like to learn more abo sions! We will be come join us for our stargazing ses have! happy to answer any questions you
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EXPLORATION
SPACE EXPLO R AT I O N NICO FENDY WIJAYA (NTUAS)
HOW DID IT ALL BEGIN? Space Exploration started in the middle of the 20th century and accelerated during the Cold War between two major powers – the United States and the Soviet Union. It began with the success of the first artificial satellite, Sputnik 1, into space and first cosmonaut Yuri Gagarin to orbit Earth in Vostok 1 by the Soviet Union. USA then responded with six Apollo missions to explore the moon. However, one of the most significant space programmes was the Voyager program involving Voyager 1 and Voyager 2.
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VOYAGER 1 AND 2
THE JOURNEY
V
oyager 1 and Voyager 2 were launched in 1977 to take advantage of a rare alignment of the planets, a configuration that occur only once every 176 years, that enable the craft to go from planet to planet accelerating as they enter the gravitational field of each planet. Their primary mission was to study planets in our solar system and now both Voyagers have their new mission which is exploring interstellar space. Now, after 3.5 decades of successful operation, the two spacecraft are sending back information on their flight to interstellar space. Along the
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way they have revealed the solar system beyond our imagining. Such as, a volcano erupting from a moon Io, the possibilities of liquid water ocean under the icy crust of Europa. Voyager 2 is the only spacecraft to have gone by Uranus and Neptune. Everything we know about those planets, we know from Voyager.
EXPLORATION
WHERE ARE THE VOYAGERS NOW?
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years after launch, by the year 1990, the voyager craft finally began their journey through the galaxy. They run on plutonium powered radio isotope thermoelectric generator which doesn’t last forever. So, scientist have to shut down instruments one by one. One of the instrument that remains working is the magneto meter that measures magnetic field from the solar wind. And from the magnetometer data, we know that Voyager 1 had crossed the heliosphere, making it the first spacecraft in interstellar space. They will keep sending valuable data back, until their power begins to run out. They will finally go dead in year 2025. Voyager 2, will be heading south toward constellation Sagittarius, travelling 16km/s, it is expecting to pass 4 light
in the heavens, 290000 years from now. Its twin will continue on a north track to a relatively empty region of our solar neighbourhood. They will become silent emissaries from planet earth and brought message in a disk encoded images of life on earth, greetings in 55 languages, a selection of music and natural sound.
years from Sirius, the brightest star
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FUTURE OF SPACE EXPLORATION
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his year, on the 55th ceremony of first ever manned spaceflight, British physicist Stephen Hawking, founder of Facebook, Mark Zuckerberg, and Russian millionaire, Yuri Milner, announced to work together on spacecraft designed to reach another star. This project is called Breakthrough Starshot. This project will send hundreds of mini spacecraft each weighing only a few grams, equipped with camera, power supply, navigation and a communication device. A rocket will bring the mini spacecraft to space and each of them will extend their
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sails which will get propulsion power from a powerful laser shot from the earth and these craft are expected to reach up 20% of the speed of light. This is much faster than Voyager 1 which has speeds 0.01% of speed of light. The possible destinations would extend to Alpha centaury, the closest star to our solar system. They will collect data and send back to earth. With a speed 20% the speed of light, it can reach Alpha Centauri in 20 years – a contrast to the conventional space craft which would require 30000 years.
S PA C E T I M E
RIPPLES IN S An introduction to Gravitational
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SPACETIME Waves and how THEY WERE detected Gao Yu (NTUAS) ASTRONICLE 2017
S PA C E T I M E
O
n Thursday 11 February 2016, announcement of gravitational wave discovery spread quickly across the globe and caused great celebration among scientists around the world. The source of these waves were from two spinning black holes known as GW150914 (a reference to the date of observation), which was discovered in 15 September 2014 but was only announced five months later due to more time needed for verification. This marks another milestone in the theory of General Relativity (GR) developed by Albert Einstein (1870-1955),
close to the speed of light ( and leads to the groundbreaking conclusion that nothing in the universe can exceed the speed of light. David Reitze, the executive of the Laser-Interferometer (Don’t worry, I will explain it later) Gravitational Wave observatory (LIGO), said in a press conference held in Washington: “We have detected Gravitational Waves. We did it.” What follows are loud applauses of the masses as they have once again realized and appreciated the far reaching implications of Einstein’s great insight into nature, even after 100 years have passed since he published his paper in 1915.
the world-renowned physicist who formulated the famous mass-energy equivalence formula, which in simple terms asserted that mass and energy, seemingly apples and oranges, were equivalent. The general theory of relativity is a theory of gravitation which postulate that the universe in which we live in can be imagined as a gigantic fabric of spacetime, where space and time has been unified to a single entity based upon ideas postulated in his other theory of relativity, known as Special theory of Relativity, which deals with phenomena concerning objects that move very
So what is the big craze about this ripples in space time? How does it affect our daily lives? What implications does it have on the search for the truth about the origin of our universe? In this exciting article the concepts of Gravitational Waves will be explained in the simplest manner (Don’t worry, no horrendous mathematics will be involved) and how it can be detected through sophisticated instruments mankind have recently developed. As it turns out, Gravitational Wave are VERY hard to detect and that what make its discovery very worthwhile.
David Reitze at a press conference in 2016 announcing the discovery of Gravitational Waves 100 years after Albert Einstein published his famous General Relativity Paper in 1915. The screen behind illustrate two black holes which circulate around a center point in space and is a strong source of gravitational waves. Image is adapted from: http://www.slate.com/articles/health_and_science/science/2016/02/carlo_rovelli_reflects_on_the_gravitational_waves_announcement.html
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A steel ball making a “dent” (Curvature) in the middle of a checkerboard fabric as illustrated above. The more massive the object is, the bigger the “dent” that it will made on the fabric. Image is adapted from: http://asd.gsfc.nasa. gov/blueshift/index.
Before delving on Gravitational Wave, it is useful to understand a bit about General Relativity. Einstein’s theory of General Relativity, in short, can be summarized by
Arthur Eddington (1882- 1994), an astrophysicist who provide one of the experimental proof of GR about the deflection of starlight around the sun (To be dis-
this famous phrase:
cussed later) was asked in 1919 whether it was true that only three people (The first two were him and Albert Einstein) in the world at that time understand the theory of the general relativity, in which he reply jokingly: “Who’s the third?”.
“
MATTER TELLS SPACE-TIME HOW TO CURVE AND SPACE-TIME TELLS MATTER HOW TO MOVE.
”
The simplest analogue this can be made is that of a ball resting in a large fabric. You can try the following experiment at home: Take a ping pong ball or tennis ball and place it on your favorite bed fabric. You will find that the ball will make a small curvature of the fabric around its vicinity. Now use a bigger object like a basketball or bowling ball (If you have it) and do the same. You will now find that the ball will make a bigger curvature around its vicinity. This is a simple but excellent summary of theory which is notoriously difficult. ASTRONICLE 2017
Left: Famous physicist Albert Einstein (1870-1955). Right: Arthur Eddington (1882-1994). One provides the theory while the other provides the experimental proof. This is how science works: A loop in which theory is verified via experiment and experiment results leads to more questions and hence theories which is to be verified by more experiments.
S PA C E T I M E Now imagine the fabric of your favorite bed to be the very space-time continuum that permeates the whole of the universe. A celestial object like the star or a planet can be imagined as your favorite sport ball that curve your bed fabric. This is exactly what the celestial object does: It distort or curve its surrounding space-time fabric around it. Any smaller object (Including light) that passes near it will be forced to travel about the curvature that the bigger object made, and that is precisely what give rise to the bending of starlight around the sun, experimentally verified by Eddington during a solar eclipse on 29 May 1919 on the island of Principe off the west coast of Africa through observing and calculating the actual position of the stars that had been shifted as its light passed around the sun (Much like how a swimming pool appears shallower than it really is via light refraction). The same distortion in space-time around the vicinity of a massive objects is what causes smaller celestial objects to revolve around it, much like a coin rotating around the curvature of a funnel (You may have seen this setup if you have visited the Singapore Science Center before). This is what drives the solar system and the stars and planets around galaxies. Hence we have a geometric description of gravity that seems at first to be in disagreement with Newton’s concepts of gravitation as a force: in Einstein’s view gravity is to be seen not as a force but a distortion in space-time that attracts nearby smaller celestial object to either fall into the bigger object, deflect its trajectory or cause it to be in an orbit. The effect that the distortion of space-time
has on any object passing through it is what we perceived as the force of gravity. Of course, we will be unable to see such distortion due to the fact that space-time is a 4-dimensional fabric (3 dimensions of space, 1 dimension of time) and humans are only able to perceive the spatial part. As mentioned, different masses will distort the space-time fabric by a different amount. The more massive objects in the universe, like neutron stars and black holes, are able to distort the fabric by a more extreme amount. For black holes, there exist a radius in which any object, including light, passing through it will be
How the deflection of starlight near massive object like the sun causes apparent shift in position of stars. Image is adapted from: http://undsci.berkeley.edu/article/0_0_0/natural_experiments
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will be pulled towards its center by its extreme gravitational field and never be able to escape from it. This radius, or boundary of no return, is known famously as the event horizon, or, the Schwarzschild radius, after the German physicist Karl Schwarzschild (1873-1916). Note that the escape velocity of a black hole is exactly the speed of light. However, this is ONLY true at the surface of the horizon and not across it! Even light cannot escape once it crosses the event horizon. It is interesting to note that black holes is also another postulation of General Relativity, and it was not experimentally verified until around 1971. Also, the term “Black hole” is coined by American astronomer John Archibald Wheeler (19112008) in 1967, not Einstein himself.
Different objects distort spacetime continuum by a different amount. The most massive objects, like the black hole, literally rips a big hole in the space-time fabric. It’s like falling into a deep hole and never able to see the light of the days again… and that is what made black holes the monster of the universe, devouring anything that crosses its path. Image is adapted from: https://s-media-cache-ak0. pinimg.com/736x/07/6c/ df/076cdf115caedd07f08cea6252c13783.jpg
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Earth by itself do distort the space-time fabric around it, as postulated by the General theory of Relativity. This cause the vicinity of space-time around it to be curved in the manner illustrated to the right. The more massive the object is, the larger the curvature it will exert. Image is adapted from: http://sedici.unlp.edu.ar/blog/wp-content/uploads/2016/02/ gravitational-waves.jpg
S PA C E T I M E So much for the lengthy introduction. Now we will go to Gravitational Waves proper. You may wonder why we do not experience GR effects in our daily lives. Why is it that Newton’s laws of gravity still hold in our solar system and not Einstein’s theory? The answer is that GR effects are more apparent at regions with very strong gravitational fields like black holes and neutron stars as they bring more significant distortion of space-time. Since these objects are fair away from Earth (And thankfully, they are!), we do not need to account for GR effects in our daily tasks, with the exception of the Global Positioning system (GPS). (Interested readers may refer to any article on the web on how GPS works.) Because neutron stars and black holes bring a much stronger distortion of spacetime, General Relativity predicts that as they move around the space-time fabric, they will emit what is known as Gravitational Waves, ripple in space-time that is akin to ocean waves or light waves but also has a significant differences which will now be explained.
Gravitational waves emitted by two black holes rotating around a common center of mass (The point in the middle surrounded by rotating black holes. The black holes will get closer to one another as they rotate (spiraling) until they merge to form a bigger black hole, with no further Gravitational waves being emitted for the time being. Image is adapted from: https://www.extremetech.com.
The effect of gravitational waves has on a mass is to simultaneously squeeze and stretch the mass in 2 directions as it passes through in the manner described in the picture. The arrow represents the direction of influence of the wave on a person. It is akin to a jelly blob that bounces continuously after being tapped on. Sound squishy isn’t it? Image is adapted from: http://www.lnl.infn.it/~auriga/auriga/grav_wave.html
Gravitational Waves are known to be transverse waves, meaning the direction of its propagation should be perpendicular to the vibrations or oscillations of the medium that carries it. However, unlike a water wave, which vibrates its medium (the water molecules) in the up-down direction while the wave move forward, Gravitational waves simultaneously squeeze and stretch the space-time fabric in two perpendicular directions instead of one like the water wave. A good illustration of such abstract concepts is illustrated below. (Hypothetical situation where gravitational waves are large enough for us to feel its effect) The main idea of the pictorial representation above is to illustrate that what gravitational waves do is to distort space-time fabric in the same way above or how some jelly bounces when tapped on. By vibrating both in the x and y direction (left and right, up and down), we have illustrated how gravitational waves disturbed the space-time fabric in two perpendicular di-
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rections instead of one. The grids shown above is for a small piece of space-time fabric-- the same concept applies to the whole of the fabric that permeates the universe. However, like water waves encountering various obstacles along the way that slow it down, gravitational waves can also be “slowed down” in the sense that its peaks and troughs, which are typical features of transverse waves, will become smaller and smaller with distance and time. We
“
...BY THE TIME ANY GRAVITATIONAL WAVES WOULD ARRIVE AT EARTH, ITS PEAKS WOULD BE SO NEGLIBILY SMALL THAT IT CAN BE HARDLY DETECTED ON EARTH.
have note that neutron stars and black holes are very far away from Earth. Adding on the fact that space-time, unlike your favorite bed sheet, is actually “stiff”, this would means that by the time any gravitational waves would take to arrive at earth, its peaks would be so negligibly small (To a value smaller than or equal to atomic sizes) that it can hardly be detected on earth. Furthermore, with seismic waves, sound waves and other form of vibrations that permeate Earth every
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day, gravitational waves are significantly “drowned out” by other interferences. It is no wonder that we have been unable to detect gravitational waves for 100 years. Actually, the presence of gravitational waves demonstrates that gravity, like light, needs time to travel through space-time before it reaches us and we feel its effect. This is similar to telephone calls where time (albeit very little of it) is required for the signal to reach from your phone to your friend’s phone through telecommunication satellites for them to receive your call. This means that gravity also travels at the speed of light and gravitational waves serve as the ”signal” to propagate “information” to faraway objects for them to receive it and “react” to it. Despite the difficulty, through advancements in technology in scientific instruments over recent years, scientists finally found gravitational waves in February 2016 through a high-tech instrument known as the Laser-Interferometer Gravitational Waves Observatory (LIGO). Two LIGOs is built in the USA, one in Hanford and the other in Livingston. Both LIGOs are managed by Caltech and MIT and supported by the National Science Foundation of America.
S PA C E T I M E
LIGO
DETECTING GRAVITATIONAL WAVES WITH
At first, LIGO doesn’t look very spectacular, does it? You may wonder why there are two long tubes orientated perpendicular to one another. You may also wonder why they are two of them built in the US and being situated far apart from one another. LIGO is designed to be VERY sensitive to any vibrations from nearby to hundreds of kilometers away. If the two LIGO were close to one another, both would detect the same vibrations at the same time: from sources on earth AND the gravitational waves. Thus it would be hard to distinguish the vibrations from the earth from gravitational waves.
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However, if the two LIGO were placed far apart, both will not detect the same vibration from earth but will detect the same gravitational waves at the same time, as gravitational waves spanned a huge distance through earth as compared to local vibrations. Comparing data from both facilities will enable scientists to rule out the vibrations from earth itself and look for identical signals that occur at the same time in both locations Thus the two LIGO facilities help one another to filter out local vibrations and concentrate on detecting gravitational waves. More LIGOs can be built to help increase the reliability and accuracy of detection. Going back to the two spinning black holes, it turns out that as they spiral towards one another, the frequency in which the gravitational waves are emitted increases. As a result, the frequency
in which gravitational waves are detected at about a few milliseconds before merger should be very large. The two LIGOs, on that fateful day, both detected the essence of the gravitational waves illustrated above. Since both of the observatories detect almost the same signal albeit with a very small discrepancy, they have concluded that the presence of gravitational waves is true, and once again Einstein’s theory of gravitation withstood the test of time! Einstein would be very proud of himself if he was still around today. Note that the entire process of black hole merging can occur as quickly as within a split second. However, since black holes are far away from earth, what we detect is the reminiscent of such event occurring from thousands or millions of light years away, meaning that the original event occurred a thousand or million years ago.
Image adapted from: http://www.thephysicsmill. com/2016/02/12/ligo-gravitational-wave-source/
The diagram above illustrates how the gravitational waves signals evolved with time as the two black holes get close to one another. The orange signal is the one picked up from Hanford’s LIGO while the blue signal is the one picked up from Livingston. The signal is a plot of frequency against time. As the two black hole merges, the frequency of the signal will become very large. This occurs for a very short time span before the frequency decreases abruptly after the merger, known as the “ringdown” in the diagram below. The signal plot gives us a “picture” of what happen to the two black holes without us needing to observe it directly. (And we can’t because nothing can escape from a black hole!)
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S PA C E T I M E
HOW DOES LIGO WORK?
A schematic diagram of LIGO. The wave pulse travelling through the interferometer is of the same frequency or wavelength. Image is adapted from https://www.sciencenews.org/article/gravitational-waves-explained
A laser source generates a continuous wave pulse of a single frequency which passes through the beam splitter located at the center. The role of the beam splitter is to split the light so that it travels in two perpendicular directions illustrates above. The two long tubes of LIGO are called detector arms. At the end of each detector arm, contains a mirror. It reflects the laser beam back to the beam splitter. The two laser pulse from each end of the detector arm will meet each other at the beam splitter and undergoes wave interference (Laser is a light wave), where two waves combined with one another to form a standing wave, wave that does not propagate with time. If you have ever played a musical instrument like the guitar, you would have seen standing wave in action when you strum on the string at different frequencies. The combined wave from two detector arms reaches the light detector and converts it into an electrical signal for data analysis. Normally, like the standing
Laser beam interference in LIGO is analogue to standing wave generated due to interference from mechanical string waves which form the basis of how most string instrument, like the guitars, works to generate music of different tone. Image is adapted from https://1.bp.blogspot.com/-2FNtqF-nkOA/U2SpjoJB8UI/AAAAAAAAEyA/_ DVJ8f07Lug/s1600/default_web.jpg
wave strings shown on the picture, laser beam light waves cancels one another out when combined (interfering with each other) and the resultant wave generates a zero signal on the light detector. However, with the presence of gravitational wave, the mirrors at the ends (which have masses), get influenced by it and “squeeze and stretch� by a very tiny amount, which means that the mirrors vibrates due to such waves. Such vibrations alter the distance the two beams travel with respect to one another. This difference in distance implies that the individual laser beam waves are not perfectly aligned and hence do not cancel out. This time a nonzero signal will be generated. It is important such vibrations are not mistaken for events from Earth itself, therefore emphasizing the sensitivity and hence high technical requirement on the instruments. It is this reason that we have not detected gravitational waves until recently.
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About five months after their first detection, LIGO scientists have confirmed a second detection of gravitational waves from two colliding black holes GW150914 and GW151226. More information can be found on the LIGO website. Because of the wide success of LIGO, other countries apart from the US are embarking on their own quest for gravitational wave astronomy via building their version of LIGO. Some examples are: 1. LIGO in India (Planned) 2. GEO 600 in South of Hanover, Germany 3. VIRGO in Cascina, Italy (Under construction) 4. KAGRA in Japan (Under construction)
For now, all of the LIGOs are situated on Earth. However, NASA has planned for a laser interferometer consisting of satellites placed in strategic positions so as to detect gravitational waves from stronger sources like merging supermassive black holes or Primordial ones from the relics of the big bang. The project is called the Evolved Laser Interferometer Space Antenna Project (eLISA), proposed to launch in 2034.
We are now at the beginning of the era of Gravitational Wave Astronomy. It is hoped that more gravitational waves apart from those of spinning black holes or neutron stars can be detected in the near future – like those from Pulsars, Quasars and the Big Bang. Such gravitational waves would allow scientists to understand more about the origin of the universe as typically strong sources of gravitational waves are situated far from Earth (peaking further back in time because the wave takes a longer time to reach us). General Relativity has become more than a subject of intellectual curiosity and it is hoped that more verification from the theory can be found experimentally. What a wonderful time to be alive!
FOR MORE INFORMATION Webpage on LIGO : https:/www.ligo.caltech.edu/ page/what-are-gw Why we need two LIGOS: https://www.ligo.caltech.edu/ page/ligo-detectors
Artist’s impression of eLISA satellites detecting gravitational waves from a black hole.
Image is adapted from https://science.nasa.gov/missions/lisa
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Schematic setup of LIGO and how it works in simple terms: https://www.sciencenews.org/ article/gravitational-waves-explained Wikipedia article on the NASA LISA project: https://en.wikipedia.org/wiki/ Evolved_Laser_Interferometer_ Space_Antenna The “squeezing” effect ofravitational waves: http://www.lnl.infn.it/~auriga/ auriga/grav_wave.html
UNIVERSE
FROM THE SMALLEST
TO THE B
THINGS IN TH RAYMOND (NTUAS)
A
t 10:56 p.m. EDT, July 20,
knowledge to allow us to investigate
1969, with more than half
the place where we live–the universe.
a billion people watching
Today, the size of the observable uni-
on television, Neil Armstrong climbs
verse is so enormous that
down the ladder of lunar module Ea-
even light will need 93 bil-
gle and proclaims, “That’s one small
lion years to travel across
step for a man, one giant leap for
it. Humans have spent a
mankind.” This is probably one of
tremendous amount of
the greatest achievements in the his-
effort to study all matter
tory of mankind. Yes, at that monu-
inside the universe, from
mental day we have landed Apollo
the smallest to the biggest,
11, the first manned lunar mission,
yet we are still far from a
on the moon. Before then, reaching
complete understanding.
TODAY, THE OBSERVABL IS SO ENORM EVEN LIGHT W 93 BILLION TRAVEL AC
the moon was only a metaphor. A long time has passed since that day.
Now, what do we mean by “under-
We have gathered more scientific
standing” something? We can imag-
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T
BIGGEST
HE UNIVERSE ine that all things which constitutes
gather knowledge. There are many
this universe as a great chess game
things that we already know and I
being played by some godly being and
cannot possibly elaborate on all of
we the observers of the
them in this article. But you have
game. We do not know
probably ever asked yourself what
the rules of the game.
the big picture of this universe and its
We only wait and watch
constituents is. This article is intend-
the game. We might not
ed to give a very limited big picture of
be able to find out all
the cosmos.
SIZE OF THE LE UNIVERSE MOUS THAT WOULD NEED N YEARS TO CROSS IT.
the rule. But if we have much patience, if we watch long enough, we may become convinced
about some of the rules. We are actually the only known species that have some systematic way to acquire and
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UNIVERSE
WHAT IS OUR UNIVERSE
MADE UP OF? I t is said that the Ancient Greeks were the first to conceive of the idea that there are objects with no size which build up this entire world through their interactions. They called these objects atoms, from the Greek word, ‘atomos’ which means indivisible. Of course, we now know that we can split atoms into the nucleus – the center of an atom – and electrons that surround it. We are able to observe the world in tinier and tinier detail through microscopes of increasing power and we are also able to design experiments to detect even smaller things than what we can see with our most powerful microscope. With this in mind, it is natural to wonder what are the objects serving as the most
basic building blocks of this world.
We believe that we have found some of these so-called fundamental particles. According to the standard model of particle physics, there are two types of fundamental particles: matter particles, the ones which combine to construct the world around us, and force carriers such as the photon, which is responsible for “carrying” electromagnetic forces which interact with charged matter particles. These particles that we believe are the most fundamental particle can be summarised in the table below.
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So, as you can see in the table, the most As you may already know, the nucleus fundamental particles are six quarks (up, of an atom consists of protons and neudown, charm, strange, top, and bottom) trons bounded by strong nuclear force. and six leptons (electron, Electrons surround the muon, tau, and their renucleus like a “cloud”. spective neutrinos) that This structure is called YOU CAN IMAGINE HOW SMALL, constitute matter and five an atom. Atoms join toAND ALSO SIMULTANEOUSLY, gauge bosons (gluon, phogether to become a molton, Z boson, W boson, ecule. Molecules made and Higgs boson) which the bigger and bigger carry fundamental forcstructures that can be es, allowing matter to interact with each seen by our eyes, living or inanimate, evother. Quarks and leptons have their reerything on the Earth. Earth is only one spective counterparts which are called planet out of eight planets orbiting the antiparticles. The electron, for example, Sun, and the Sun only one of hundreds of
HOW BIG WE ARE.
has a counterpart named the anti-electron or positron. When a particle meets its antiparticle, they annihilate each other and
billions of stars in our galaxy. And our galaxy, the Milky Way, is only one of around fifty galaxies in Local Group, a typical gal-
release energy in the form of a photon. All other particles and matter are built from these fundamental particles. For example,
axy group, yet the Local Group is a rather small galaxy group compared to other galaxy clusters in the Lainakea Superclu-
a proton consists of two up quarks and one down quark. The proton is an example of a baryon. Every baryon consists of three quarks. There are other species of particle which consist of a quark and an antiquark is called a meson. An up quark with an anti-down quark together constitute a positive pi-meson (or pion). A down quark with an anti-strange quark forms a neutral kaon. The list goes on. Our universe mostly consists of matter, rather than antimatter. Why it is not symmetric in terms of the number of matter and antimatter is still
ster which encompasses hundreds of galaxy groups and clusters. You get the idea. We’re very big and very small at the same time.
more or less a complete mystery.
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To get a better sense of how big and small we are, go to http://htwins.net/scale2/ for a nice graphic!
UNIVERSE
STORY OF A STAR T he first word that will come to your
star cannot burn forever. When all the hy-
mind if you hear the word “astronomy” is probably ‘star’. Our ancestors were very skilled at observing the
drogen is converted to helium, the core of the star will become degenerate, a state where the core of the star cannot continue
movement of the stars, hence astronomy was born. But what is a star? So here is the story. In this universe, there are some regions that are a little bit denser than a complete void. This “cloud” of dust, hydrogen, helium, and other gases are called nebulae. A nebula will collapse due to its own gravity and at some moments, certain part will become denser than its surrounding. Dense enough so that the molecules start to collide with each other, hence increasing its pressure and temperature. This part is called a protostar. Protostar will further collapse until the centre part is hot enough to ignite nuclear fusion. When the nuclear fusion starts, the pressure will increase dramatically and at a certain time, the nuclear and thermodynamical pressure will stabilize the gravitational collapse. When the radiation pressure outward balances with gravity pushing inward, the star is born.
the nuclear fusion. At this point, the rest of the story depends on the mass of the star. Eventually, all stars will end as either a white dwarf, brown dwarf, neutron star, or black hole. The process to the end varies from star to star depending on the mass and composition. Some will directly reach the end slowly, others will expand to a red giant and begin nuclear reaction in the shell again, and the rest collapse violently in a supernova. The more massive stars may also be a nursery for heavier elements up to iron. Elements heavier than iron cannot be produced naturally inside a star – only a supernova can produce such elements. Hence, the existence of such elements in Earth’s core is evidence that our solar system is the remnant of a supernova occuring before Sun was born.
The star will continue to burn all its fuel, primarily hydrogen (especially for stars with a typical mass like our Sun) through a nuclear chain reaction named a proton-proton cycle. In stars slightly more massive than the sun, carbon-nitrogen-oxygen fusion reaction or more commonly known as the CNO cycle may start. But a
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This active stellar nursery located near the constellation Orion contains thousands of young stars and developing protostars. Taken with the Spitzer Space Telescope Credit: NASA ASTRONICLE 2017
UNIVERSE
E
X
I
P A N UNIVE
n the 1920s, Edwin Hubble realised that almost all galaxy groups and clusters are receding from us. He concluded this by photometry measurement of emission lines that are redshifted to longer wavelength. He hypothesized that ev-
cal baloon. The distance between two arbitrarily chosen points on the surface of the baloon increases uniformly with the inflation. We can draw an analogy in the example below. The bread represents space, while the raisins represent various objects
ery point in this universe is receding with respect to each other with the speed that is proportional to the distance between the respective points. Numerous scientists have tried to explain this phenomenon. The accepted theory is that the universe is actually expanding in a sense that the scale of the space itself changes. We can imagine the expansion as an inflation of a spheri-
in space. As the bread expands, the raisins grow further apart relative to each other. Now, if the universe is expanding, then there must be a time where this universe converged at one point. But, how large is a point? When the universe is smaller than certain size, the laws of physics are no longer applicable. This point is called
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N D I ERSE
N
G
a singularity. Current estimates place this
postulate the existence of dark energy to
moment at around 13.8 billion years ago. The initial expansion of the universe from that point is called the Big Bang. The Big
explain this, this is the energy that keeps the expansion of the universe accelerating despite gravitational attraction of matter.
Bang is not a literal “bang�; it is not a huge explosion. Rather, the Big Bang is when the singularity ended and physical laws
According to the current calculation, dark energy comprises as high as 68% of the total energy in this universe. The ultimate
began to govern the universe. According to some studies[3], the universe’s expansion was decelerating until approximately 5 billion years ago due to the gravitational attraction of the matter content of the universe, after which time the expansion began accelerating. The source of this acceleration is currently unknown. Scientists
fate of this universe is, again, more or less a complete mystery.
The bread represents space, while the raisins represent various objects in space. As the bread expands, the raisins grow apart relative to each other.
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O
Overs
OE P
seas Exposure Programme 2017
B I N T A N
Day 1 We started our trip with a ferry ride from Singap
ore to
Bintan on a cheerful note when we were greete the hilarious welcome sign on the bus that bro
d by
us from the ferry terminal to the hotel. There
ught
was an
abundance of beautiful cloud formations in the sky that helped to alleviate our spirits. The only pro blem
was when these clouds remained in the sky thro
ugh-
out the day and caused a change in our starga zing plans as they were covering the stars. Howe ver, we made up for the lack of stargazing with a gro up din-
ner to have a taste at the local delights and als exciting trip to a supermarket where we laid our on novel Indonesian products.
o an
eyes
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Day 2
We left our hotel in the morning for a mangrove tour and were very lucky to be able to see a variety of animals including snakes, monitor lizards and monkeys. After eating local food such as mie goreng and kerupuk udang, we went to visit Crystal Lagoon in Treasure Bay, which is currently the largest man-made lagoon in Southeast Asia, and had a lot of fun taking photos with the crystal clear water as our background.
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B I N T A N
It was a short trip to Lagoi Beach from Crystal
Lagoon
and we had a successful solar observation and scope workshop there, where we managed to
tele-
see the
sun without any of its sunspots as it just happen be the start of a new solar cycle. We had a sta
ed to
rgaz-
ing session later that night and were fascin ated by the abundance of stars and the stories behind them, especially since a fair number of the participan ts had no prior knowledge of astronomy.
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Day 3 / 4 We paid a visit to the Banyan Tree Temple and the Senggarang Chinese Village and had seafood for dinner. It was exciting to see the fishermen go out to catch our dinner for us and to hear the soothing sound of the waves softly lapping against the shore. It was very relaxing to take an early morning walk along the beach and to go for a free and easy shopping session at Ramayana Mall. We left for the ferry terminal after shopping (with some of us buying bagful of snacks) and bid farewell to Bintan.
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Nanyang Astronomical Society
If you are interested in stargazing or learning more about astronomy, do join us for our stargazing or weekly astronomy sharing sessions! For more information on our activities, watch out for updates on our official Facebook channel or our Website. (Links Below!) Clear skies ahead!
https://www.facebook.com/ntuastro/ https://clubs.ntu.edu.sg/ntuastro/