The Seasons

TOPICAL SCIENCE

SEPTEMBER 2018

S E P T E M B E R

AUTHOR: MARGARET FRANKLIN

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Topical Science

The Seasons In this issue

When does Autumn Start?

In September, schools reopen after the Summer holidays and we (in the Northern Hemisphere) tend to think of September as the first month of Autumn, with the season starting on the first day of the month. However, some people believe that Autumn does not really start until the equinox. But our Celtic ancestors had a different view. The Irish name for September is ‘Meán Fómhair’, which literally means ‘the middle of the harvest’’.

Since harvest time occurs in Autumn, the Celts regarded September as the middle of Autumn. This would make August (or ‘Lughnasa’, as the Celts called it) the first month of Autumn.

October was known as ‘Deireadh Fómhair’, or the end of Autumn. Winter started on the first of November.

Page 1. The Start of Autumn

Page 2. The Astronomical & Meteorological seasons

Page 3. Seasonal Confusion

Page 4. The cause of the seasons.

Key Dates for the seasons for the rest of 2018 Equinox 23rd September.

The rays of the sun fall directly on the Equator. The hours of daylight & darkness are of equal duration.

Samhain

Solstice

1st November

21st December

In times past, this date marked the first day of Winter and was the start of the Celtic New Year.

On this date, the sun’s rays fall directly on the Tropic of Capricorn. The Northern Hemisphere has the longest night.

The last roses of summer often continue to flower during the Autumn.

The Seasons The starting date for each season depends on whether you ask an astronomer or a meteorologist.

The Astronomical Seasons

Winter The Celts began the reckoning of their year with Winter, starting on the first of November. They celebrated the New Year, or ‘Samhaim’, with various rituals.

In Ireland, the Hallowe’en festival is derived from this. The Celts used the Julian calendar, which was introduced by Julius Caesar, in the first Century before the Christian Era. Their calendar was closely connected with the best dates to sow their crops, to ensure they would have a good harvest in the Autumn.

Astronomers use the dates of the Equinoxes and the Solstices to determine when each season begins. We have two equinoxes each year, in March and in September, when the rays of the sun fall directly on the equator and day & night are of equal duration. We also have two Solstices, in June and in December.

The Meteorological Seasons According the Meteorologists, each season starts on the first day of the month in which a solstice or an equinox occurs.

Thus, Autumn begins on the 1st day of September, Winter on the 1st of December, Spring on the 1st of March & Summer on the 1st of June.

Christmas is the great Winter Festival in Christian communities.

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TOPICAL SCIENCE

AUTHOR: MARGARET FRANKLIN

SEPTEMBER 2018

Seasonal Confusion

Begonias flower in Summer and last well into Autumn.

From the scientific point of view, the Astronomical reckoning of the seasons is as valid as the Meteorological, but it is often tradition that carries more weight with non-scientists.

The June solstice, which is the longest day of the year in the Northern Hemisphere, was traditionally celebrated as ‘Midsummer’s Day’. This would mean that summer actually started about six weeks before the solstice, around the first week in May. Indeed ‘Mayday’ celebrations traditionally marked the beginning of summer. There are twelve months of the year, so each season last about three months. Traditionally, the months of summer are May, June & July. This makes August the first month of Autumn, which is consistent with the Celtic tradition. September and October are also Autumn months, while the start of the Celtic Winter and New Year was celebrated on November 1st.

This traditional approach is closely related to the modern science of Phenology, studying the timing of natural biological events in their annual cycle. Such events include the trees coming into leaf, the flowering of plants and the fall of the leaves in Autumn. In the U.S., Autumn is known as the ‘Fall’.

Tulips in Springtime Tulips provide a splash of colour in late Spring, but their flowering season is short.

As gardeners know, different plants come into flower at different times during the year. The earliest spring flowers are usually the snowdrops, which may bloom in Ireland as early as January, followed in succession by crocuses, daffodils, tulips and finally bluebells (or hyacinths).

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What causes the Seasons?

The tilt of the Earth’s axis is what causes our seasons. This has been explained in detail in the June 2018 issue of ‘Topical Science’, which dealt with the June Solstice. Our planet Earth has two types of motion; it rotates on its axis every 24 hours, giving us day and night, while it also revolves around the sun, taking approximately 365.24 days to complete its orbit.

The earth’s axis of rotation is tilted at an angle of 23.5 degrees to the plane of its orbit around the sun.

This means that the direct rays of the sun fall at different latitudes at different times of the year. At the September equinox, the rays of the sun fall directly on the equator, so that day and night are of equal duration all over the globe. After that date, we in the northern hemisphere will have gradually increasing longer hours of darkness than daylight, until December 21st, when the rays fall directly on the Tropic of Capricorn, which is 23.5 degrees south of the equator. This is when we will have the shortest day of the year. The weather is colder in Winter for two reasons. Firstly, we have fewer hours of daylight and therefor a shorter time for the sun to heat our part of the planet each day. Secondly, the sun’s rays are reaching us at a more oblique angle, so the energy is more spread out and therefor has a lesser heating effect.

But, as the poet Shelly said, ‘If Winter comes, can Spring be far behind?’

The Autumn Leaves In Autumn, the leaves change colour before they fall,, creating a pleasing display in parks, gardens and in the countryside.

The Author, Margaret Franklin Margaret Franklin is a retired chemistry lecturer. She spent most of her career at Athlone Institute of Technology, in the Midlands of Ireland. For several years, Margaret wrote a column entitled ‘Topical Science’ for a local weekly newspaper. It is now published on-line as a monthly newsletter, covering science topics for the information of the general public.