Astronicle
2016
NTUASTRONOMICALSOCIETY 1
Solar Eclipse
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Feature Article This upcoming year 2016 will be embellished by a natural phenomenon known as a solar eclipse. Solar eclipses have played major roles in history, from being used as omens to stop wars to being as used as the means to prove of the general relativity theory.
Joandy Leonata Research and Resource Officer
Figure 1: The first observational proof of General Relativity of Eddington Eclipse.
Being such a rare sight at various places across the globe, any solar eclipse is always enthusiastically looked forward by people. Before bringing about the upcoming 2016 
 solar eclipse, let’s talk more about the science behind what makes the eclipse so awesome.
Section 1
How does a solar eclipse occur?
A solar eclipse will occur on the condition that the moon moves directly “in front” of the Sun, effectively overlapping it. With the sunlight blocked by the moon, it casts shadow on the surface of the Earth. Of course, the idea is relatively simple. But why are total solar eclipses so rare at some specific places and why does it happen in the first place? Now we’ll answer the latter question first. Scientifically speaking, it all comes down to a mix of orbital alignments and cosmic coincidences. The sun just happens to be 400 times bigger than the moon and 400 times further away. Only with these amazing coincidences, the amazing total solar eclipse can occur. As for the rarity, this is due to the fact that planets including Earth orbit the sun along the ecliptic plane (ecliptic from the word eclipse as solar and lunar eclipses happen on this plane), but the moon orbits the earth on a plane that is tilted at an angle of about five degrees to the ecliptic. In other words, on each orbit around the Earth (which lasts for 27 days), the Moon only crosses the ecliptic twice and at two locations. Furthermore, the orbital plane of the moon wobbles, causing it to ‘rotate’ about its axis like a spinning disk. Add in the revolution of the Earth and other space phenomena, we get numerous factors in determining types and date of both lunar and solar eclipses. On average, a total solar eclipse occurs somewhere on Earth about every 18 months. However, from any one location on Earth, total eclipses take place on average only once in several hundred years. So that is how rare a total solar eclipse is.
Figure 2: The various positions of the moon favorable for an eclipse.
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Section 2
Types of Solar Eclipse Moving Along, The Shadow Of The Moon Has Distinct Parts Of It That Determine What Kind Of Solar Eclipse Can Be Seen
Figure 3: The different parts of the moon’s shadow.
From A Certain Place. These Distinct Parts Are:
1. Umbra: The innermost and darkest part of the Moon's shadow. The Sun's light is blocked in places on Earth where the umbra falls. The Sun's disc is not visible anymore. 2. Penumbra: The outermost and the lightest part of the Moon's shadow. Only part of the Sun's light is blocked in places on Earth where the Moon's penumbra falls. The Sun's disc is partly visible. 3. Antumbra: The Moon's antumbra lies beyond the umbra. It appears with the growing distance from the Moon. From Earth, the Moon appears smaller and cannot completely block the Sun, so the Sun's outer rim is still seen.
There are 4 types of solar eclipses and they are determined by what part of the Moon's shadow falls on the Earth:
Total: A total solar eclipse takes place when the Moon completely covers the Sun and casts its umbra and penumbra on Earth. A total eclipse of the Sun can only take place when the Moon is at the closest point from Earth. You can experience a total solar eclipse if you're in the path of the Moon's umbra.
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Partial: Partial solar eclipses happen when the Moon does not completely cover the Sun's disc and casts only its penumbra on Earth. Annular: Annular solar eclipses occur when the Moon's antumbra falls on Earth. The Moon's disc covers the center of the Sun's disc, leaving the Sun's outer edges uncovered. An annular eclipse of the Sun can only take place when the Moon is at furthest point from Earth. Hybrid: Hybrid eclipses are rare. They happen when an annular eclipse turns into a total solar eclipse (as Moon also gets closer to Earth when the eclipses occur).
Figure 4: The three main types of solar eclipses.
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Solar Eclipse from Singapore in 2016 The solar eclipse in 2016 will occur on 9 March 2016, so mark that date on your calendar. From Singapore, the eclipse is 86.8% partial solar eclipse. Some stats on the occurrence can be found below. Start
Maximum
End
Time (GMT+8)
07:22:57
08:23:43
09:32:53
Altitude of Sun
2˚
17˚
34˚
The schedule of the solar eclipse from Singapore from 2016.
If you actually want to see a total solar eclipse, you could go the Palembang or the Ternate island in Indonesia.
Tips to look at the solar eclipse from Singapore: •
Wake up early (first thing to note of course)
• Prepare the equipments needed to look at the eclipse (never look with your naked eyes!) such as: o Solar glasses (special filtered glasses to look at the sun) o Telescopes with solar filter o Camera if you want to capture the beauty of the eclipse •
Prepare to be amazed!
And of course if you don’t have any of those and still want to take a proper look at the Sun, come join us Astronomical Society at SRC field on 9 March! Feel free to contact us via Facebook for more details!
Image Credits: 1.https://jcconwell.wordpress.com/2009/05/31/this-first-observational-proof-of-general-relativity /eddingtoneclipse/ 2.http://www2.astro.psu.edu/users/caryl/a10/lec2_2d.html 3.https://en.wikipedia.org/wiki/Eclipse 4.https://lasermom.wordpress.com/2012/05/20/solar-eclipse/
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Chapter 2
Nebulae Winston Lim
 Research and Resource OďŹƒcer
Figure 1: Photograph of the Crab Nebula of the Taurus constellation. Taken by the Hubble Space Telescope.
Section 1
Nebulae – What are they? Nebulae are clouds of dust and gas, and are the birthplaces of stars. They are visible to us because of the stars, or more accurately, the death of stars around them. They capture our imagination and inspire awe about space, even among astronomers to this day. Photographs of nebulae taken by special telescopes detecting light in spectrums we cannot see, show us their Figure 2: Here is a photo of the Milky Way. You can see the dark clouds which are actually regions of dust/gas.
beauty and power. Their story has two beginnings – one with stars, and another with the emptiness of space.
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Section 2
The Interstellar Medium Space was once thought to be completely empty. A
Dust and gas are actually found everywhere in the
perfect vacuum. Nothing inside at all. It was not until
universe! In the case of nebulae, dust and gas in these
the early 1900s that astronomers realised that the
regions are particularly denser than elsewhere. Gravity
dark spots on the Milky Way were actually some
slowly pulls the dust and gas around into denser
‘stuffs’ blocking out light from the stars behind them.
regions; clouds of dust and gas. These regions are
These ‘stuffs’ were later concluded to be dust and
called nebulae.
gas. In fact, dust and gas fill the gaps between stars, planets and galaxies, everywhere in the universe. They are just very thin! (They comprise of only an average of 1
atom/cm3
– even the best labs on earth cannot
achieve this level of vacuum. In comparison, earth’s
Although nebulae are still much, much thinner than our air, they may contain very dense regions within them. These especially-dense regions may turn out to be star-forming regions.
air consists of 1019 atoms/cm3). These thin ‘stuffs’, which are found everywhere, are called The Interstellar Medium.
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Section 3
Stars The Orion Nebula is an example of a star-forming region in space. Stars are big part of the nebulas’ story. To understand this, nebulas are categorized into 5 main types: 1. Emission Nebulae – clouds of mostly H2 gas emitting light after being excited by radiation from nearby stars.
It is 15 light-years across. Nebulae form stars by having gravity compress its hydrogen gas into a dense region. As the compression occurs, the cloud inside this dense region begins to spin into a smaller and smaller space. Thanks to the law of conservation of angular momentum, this spinning gets faster and
2. Reflection Nebulae – clouds of gas reflecting light from nearby stars.
faster as it is encased in a tinier region. The spinning and
3. Planetary Nebulae – clouds of gas released from the death of a red giant.
and gradually, as temperatures reach millions of Kelvin, nuclear
4.
Supernova Remnants – aftermath of a supernova.
This process fascinates because it answers questions about how
5. Dark Nebulae – clouds visible because they block light from the stars behind them.
we came to be. The sheer magnitude of everything happening in
Each type of nebulae has its unique properties. Not all nebulae form stars but as far as we know, they are the places where stars are born.
known to us, but it seems that the more we learn, the more our
compression builds up heat and pressure inside the region’s core fusion will occur and a star is born.
nebulae is mind-boggling. Not everything about the universe is minds are blown. Another interesting science bit for you guys to learn is astrochemistry and astrobiology. Before the interstellar medium, we thought that space was void of all chemistry matters.
The photograph shown on the next page is the Orion Nebula. You
It seems that we were dead wrong! Again!
can see it in the clear night sky in the Orion constellation. It sits in our Milky Way galaxy and the bluish white region at the centre is a group of four very powerful stars lighting up the entire nebula. 5
Photographs provided by: 1.
NASA
2.
www.astronomy365.net
3.
www.rawastrodata.com Figure 3: Photograph of the Orion Nebula
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CHAPTER
3
Supernova Explosions
Chin Zong Yang External Coordinator
A supernova is the cataclysmic explosion caused by the core of a red supergiant or a binary star system that is collapsing. The phenomenon that can easily outshine the supernova’s parent galaxy is also known as the supernova explosion. This bright explosion can be expected to radiate as much energy as a star in its entire lifespan, for a few weeks, before fading away. A supernova will end up as supernova remnant; a rapidly expanding shell of material that contains materials from the star’s core such as oxygen, nitrogen, carbon and other essential building blocks of life. An example of such remnant is the famous M1 Crab Nebula in the constellation of Taurus. Heavy metals, from iron to uranium, will be produced in trace amounts as well, in much more massive explosions. Shockwaves carrying elements generated by supernova explosions can trigger the formation of new stars and planets in other nearby nebulae, including our star system that eventually gives rise to life. These new elements are then absorbed in other nearby nebulae to form new stars due to the shockwave generated by the supernova, allowing planets to form and thus, forming life. Rocks, that are made up of silicon, can only be created in a star’s core by fusion.
It is hence said that the iron in our blood, the calcium in our bones and essential building blocks in our body are made up from materials created from the cores of stars approaching supernova. It is well known that the Big Bang Theory was the scientifically accepted explanation of how our universe came to be. As theorized by the Big Bang, at the end of the cooling period the universe is known to consist of about 70% Hydrogen atoms, 28% Helium and 2% Lithium. To form heavier nuclei, lighter elements are required to undergo nuclear fusion in a high-pressure environment. For instance, in the core of a star, temperatures can reach about 15 million Kelvins during hydrogen fusion. Supernovae explosions have extreme conditions that can synthesize heavy atomic nuclei up to uranium and the following pages will explain the mechanism behind the processes that takes place.
Figure 1: This is supernova remnant SN1006 which is the remnants of a supernova explosion that occurred during the year 1006 A.D.
S ECTION 1
Supernovae Types
Core Collapse supernovae (Type II and Ib/Ic)
There are two main types of supernovae, Type I and Type II. They are classified based on their spectra nature and the shape of their light curves. Type I supernovae do not have Hydrogen light emissions and Type II supernovae can be distinguished by their Hydrogenalpha emissions (Bayer Series). There are several other classifications of supernovae - Types III to V as categorized by astronomer Frank Zwicky - but I will only be covering the two main types of supernovae, Type I and Type II, in greater detail.
As discussed earlier, most core-collapse supernovae are usually Type II supernovae. They show hydrogen spectral lines from the Bayer series as the shell of hydrogen gas from the outer layers of the star is blown off the star during supernova. Type II supernovae can also be further classified into subclasses describing its characteristics, namely II-P, II-L and IIn. Type II-P reaches a plateau in its light curve, II-L displays a linear decrease in its luminosity over time and IIn shows narrow spectral lines (type II supernovae display broad emission lines). Much more massive stars, of over 20 solar masses, will expel their outer layer of hydrogen during their red supergiant phases while burning helium or heavier elements. These massive stars are classified as Wolf-Rayet stars. When these stars undergo supernova explosion, little or no helium is present in their spectra.
Figure 13: WR124, a Wolf Rayet star with its surrounding nebula of expelled hydrogen. Image by the Hubble Space Telescope, NASA
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Type Ia supernovae (binary system supernovae) Type Ia supernovae occur only in binary systems (two stars orbiting one another) in which at least one white dwarf is involved. A white dwarf is a small, dense and bright core of a regular star that has reached the end of its lifetime. Although white dwarfs are stellar cores that have ceased nuclear fusion, common white dwarfs of carbon-oxygen composition may resume nuclear fusion if they achieve pressure and temperatures sufficiently high enough. White dwarfs themselves have a mass limit of 1.38 solar masses (Chandrasekhar mass), exceeding that number can trigger a supernova explosion or re-ignite the nuclear fusion reaction. There is also a lack of hydrogen in the core of white dwarfs, thus the Balmers series1 are not present in supernovae caused by white dwarfs. Instead, a characteristic light curve is observed, with lines of oxygen and calcium present in the initial stages of the supernova. As the supernova cools and becomes transparent to observe the core remnants, emission lines of heavy metals that are produced during the supernova can be observed. Later in the process, the decay of radioactive Nickel-56 to Cobalt-56 and then Iron-56 produces high-energy photons that are the majority of the energy output.
Figure 14: A white dwarf accreting material from a nearby giant star. Image from NASA
There are two ways a white dwarf can approach supernova. The first is via an accretion disk from a nearby star. Another way would be for two white dwarfs to collide, releasing massive amounts of energy. In the first method, many stars come in binary pairs, and it is common for one star to be more massive than the other. The more massive star dies first, becoming a white dwarf (if the mass of the star is below 10 solar masses), while the less massive star will last longer in the main sequence before reaching its red giant stage. The shedding of mass of the first star reduces the angular momentum of the system, thus reducing the 1The Balmer series is a set of wavelength of light that is emitted by a Hydrogen atom when excited.
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orbital radius and period, bringing the white dwarf closer to the second star. Soon after, the second star reaches the end of its main sequence and swells into a red giant. The white dwarf, being close to the second star, is able to accrete material from the second star’s atmosphere to itself, forming an accretion disk, and due to the further loss of angular momentum, the two stars orbit closer to each other, with orbital periods that can be as short as hours. If the accretion is long enough, the white dwarf can reach the Chandrasekhar limit of 1.44 solar masses, where anywhere above that mass the degeneracy of electrons is insufficient to balance the object’s collapse due to gravity. Once reaching this limit, the white dwarf undergoes a very brief period where it undergoes nuclear fusion of carbon, which can quickly lead to a runaway reaction, releasing enough energy (about 1 × 1044J) to completely destroy the white dwarf in a supernova. The white dwarf can also accrete material from other objects as long as it is sufficiently close, such as a main sequence star or a subgiant star. Figure 14: A Type Ia supernova in the galaxy NGC 4526. The Type Ia supernovae is used as a standard candle to measure distances in space. Image from the Hubble Space Telescope, NASA
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One useful aspect of such a supernova is that the absolute magnitude of the supernova explosion is constant with a small degree of variation. This makes Type Ia supernova a good candidate as a standard candle used to measure intergalactic distances with respectable accuracy. Other examples of standard candles for intergalactic distances include Cepheid variables and RR Lyrae variables, which also have the same average luminosity for each of the types of stars. Observation of Type Ia supernovae led to the discovery of the universe accelerating its expansion, winning the discoverers the Nobel Prize in 1998. The second type of Type Ia supernova occurs when two white dwarfs with the combined mass higher than the Chandrasekhar limit merge together. This is a very rare event, as stellar collision in the Milky Way galaxy occurs once around 107 – 1013 years. The combined super white dwarf will then collapse under its own gravity
and starts nuclear fusion of carbon. This leads to a runaway reaction and the release of massive amount of energy, completely destroying the white dwarf in a supernova explosion. Such an explosion occurred in 2003 when a white dwarf of 2 solar masses exploded. This led astronomers to propose the idea that this process is only possible with two white dwarfs in the system, since a single white dwarf system would not be able to stay over the Chandrasekhar limit for that long. This also means that the supernovae caused by this method is much brighter than the first process of Type Ia supernovae, which can cause inaccuracies in the standard candle method for measuring galactic distances.
References: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/snovcn.html
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CHAPTER 4
∏
THE DARK TRUTH ABOUT SPACE DUST
Ummu Sumaiyah Binte Eliase NTU Astronomical Society
Figure 1: BEHOLD, SPACE DEBRIS!!!!
âˆ? To the great delight of archaeologists and anthropologists, human waste and its disposal has been a conundrum plaguing the earth since the first proto-human tied a rock to its stick and made a tool. Even the writer of this article has spent many a wondrous hour staring at the odd used plastic cup placed defiantly right beside the garbage binđ?&#x;™. As we launched our rockets into space, it was inevitable that our affliction followed. But surely the problem is not too bad, right? Space debris started out innocently enough. Much like Hansel and Gretel scattering breadcrumbs as they ventured out further into the woodsđ?&#x;š, our spaceships shed paint flecks and other assorted little bits of themselves. Adding to the mess already present are dead spacecraft and spacecraft parts, residues of weapons testing and the charred remains of old satellites who have survived whatever misguided attempt at destroying them. Occasionally, these larger pieces of debris fall down to earth, much to the confusion of all.
đ?&#x;™ Perhaps the need to mark territory overwhelmed the need to live in a clean and litter-free environment. đ?&#x;š For those of us who grew up without fairy tales, imagine an old man shedding dandru. Now imagine that dandru is spinning very fast and creating more dandru every time it crashes into something. đ?&#x;› Shout out to Gravity!
Figure 2: Perhaps the answer to life and all its secrets may be found within this mysterious orb
The problem with space debris is that you can’t just leave it alone. Even the smallest speck of debris can deal quite a lot of damage given the speeds the travel at. Chunks may fall to earth, releasing possibly toxic chemicals as they burn upon re-entry, and livestock death as they hurtle toward remote areas in the countryside. The larger chunks may result in the destruction of space shuttles and space stationsđ?&#x;›.
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đ?&#x;œ There have actually been initiatives conducted by some countries in countering this issue, a comprehensive list of which may be found under the Wikipedia entry for ‘space debris’ however, I just wanted to add the picture of the two toddlers playing with flour. Aren’t they adorable?
MOM?????
Figure 3: A very inspirational picture depicting the little ball bearing that could
Cleaning it up, on the other hand, requires money and resources countries may not be prepared to provide. While space is the common property of all nations, satellites launched by a country, and the subsequent residues, remain under the ownership of a particular country. Most people simply do not feel comfortable clearing up some other country’s waste, despite the fact that the presence of space debris affects the wellbeing and scientific development of everyoneđ?&#x;œ.
Figure 4
Image credits: 1. (Visualisation of space debris orbiting earth) 
 https://commons.wikimedia.org/wiki/File:Debris-GEO1280.jpg 2. (Space debris crashed in Saudi Arabia) https://en.wikipedia.org/wiki/ File:PAM-D_module_crash_in_Saudi_Arabian_desert.png 3. (Eect of space debris impact) http://www.esa.int/Our_Activities/Operations/ Space_Debris/Hypervelocity_impacts_and_protecting_spacecraft 4. (Toddlers destroy house with flour; screen capture from video) https:// www.youtube.com/watch?v=BeFSWIsBRi4
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OVERSEAS EXPOSURE PROGRAM (OEP) The annual stargazing trip is a chance for our members to experience the beauty of space outside our sunny (and light-polluted) shore. This year, we went to Langkawi, Malaysia. Nico Fendy Wijaya Publication and Publicity Officer (Event)
Figure 1: The magnificent sunset at the Langkawi beach.
Figure 2
DAY 1
DAY 2
We began our trip in the early afternoon, with time spent in transit used for leisure activities and ice-breaking games, for event committee members and participants alike to get to know one another better. After settling down upon arrival, we then went on to try various street food such as nasi goreng, mie goreng and other local food fares. The sky was very clear and dark when nighttime arrived that day, giving us opportunities to identify many different constellations and stars on our first stargazing attempt. Armed with binoculars and telescopes, we truly immersed ourselves in the observation.
Early in the morning of the second day, we departed from a small port near our hotel for Beras Basah island, a popular resort destination. The beautiful scenery of the beach is truly a sight to behold for all, and we had a ball of time sightseeing and picturetaking. Afterwards, we visited the second island for eagle seeing, and from our boat we could easily observe large eagles catching fish. Lastly, we went to Tasik Dayang Bunting Island, a unique island with a lake inside it, and basked in the marvelous scenery of both the lake and the sea from the top point.
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Figure 3
DAY 3 Early on the third day, we visited the Durian Perangin waterfall, named after the spiny tropical fruit found in abundance around the area and spent our morning there relaxing in the rustic natural scenery. After some time spent island-hopping, we did solar observation and were able to catch sunspots! 3
Figure 4
Hungry for some more dose of sightseeing, everyone travelled to the top of the local mountain by cable car to catch some truly spectacular view from the top. On our last night in the resort town, we went to Langkawi National Observatory. There, we were taken on a detailed tour of the facilities, completed with an opportunity to used the massive telescopes there. There are solar telescope (available as a cluster of scopes!) to observe the sun as well as the usual night telescope to observe night sky objects. Needless to say, the images from the scopes were amazing!
Figure 6: The view from the cable car.
That is all for our OEP last year. We hope that you will join us for this year’s OEP at the end of Semester 1! See you soon!
Figure 5: One of the telescopes in Langkawi.
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Comic
http://safelyendangered.com/
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Designer Liu Chang
Editors Thai My Linh Jocelyn Chee Wilbert Kurniawan
Contributing Writers Koko Kaung Winston Lim Joandy Leonata Chin Zong Yong
CREDITS
Nico Fendy Wijaya Ummu Sumaiyah Bte Eliase
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