With Easter just around the corner I thought I would take a look at why Easter is a moveable feast.
The starting point for setting the date for Easter is the Spring Equinox. Astronomically speaking this can be on the 20 to 22 March, but the Christian church back in 325 AD decided to set the date for 21 March. The Council of Nicaea was a group set up by the Early Church to unify Christian practices, one of which was to set the date for Easter in accordance with Roman custom so as to unify calendars and not to coincide with the Jewish Passover.
Interestingly, Eastertime itself though has long been a time of celebration, originating in the pagan festival of Eostre. Eostre was a Germanic goddess of spring, and at the spring festival hares brought eggs as gifts. With the abundance of new season crops, feasting was a big element of the pagan festival, out of which arose the Christian festival. It was perhaps easier to honour the principles of Lent when there was not much food around!
With the equinox officially set for the 21st, this explains why Easter can be so late one year and so early the next. For example, if there is a full moon on the 19th…this is too early by the church’s calendar and therefore Easter will be late in April.
Astronomically speaking, the spring equinox happens when day and night are almost equal, not to be confused with equilux which is the when the hours of daylight are equal to the hours of darkness…the spring equinox actually refers to the time when the sun appears to cross the equator as we tilt towards summertime. Of course, the sun doesn’t move, it is Earth which is tilting on its wobbly journey around the sun. (and yes, the sun rotates but does not orbit us!).
When Orion strides into view, you know it is a sign that winter is well under way and with it, clear, dark skies (weather permitting!) due to the decrease in atmospheric disturbance. When the air is colder, the atmosphere holds much less moisture compared to the summer months. The additional moisture probably hinders the passage of starlight. Personally, I feel sad somehow when I see Orion high in the sky to the west, a visible reminder of the passing of time perhaps?
Before taking a look at the stars in Orion, it is helpful to have a broad understanding of what a light year is in order to appreciate the vast distances involved when looking at this constellation in particular, reasons for which will become apparent. A light year is the distance light travels in a year. The speed at which it travels is 299,792 km/186,000 miles per second; it takes just over 8 minutes for light to reach us from the Sun. (Distance from Sun to Earth is around 150 million km/94 million miles) So, a light year is quite some considerable distance…10 trillion km/6 trillion miles…or
10000000000000 km/6000000000000 miles
What is a star?
A star is formed out of a collapsing cloud of interstellar matter. When the pressure and temperature become so high that nuclear reactions start, that matter becomes a star. Hydrogen is converted into helium. The force of its gravity acts as a counterbalance to the nuclear reaction and keeps the star in equilibrium. Large stars are pulled towards the base of a nebula by gravity.
Nebulae are star forming regions. Stars are formed within giant gas clouds (nebulae) where dust swirls deep within them. Pockets of gas are formed which grow so big that gravity pulls more gas into the pocket. Then gradually, the pocket of gas begins to contract, and it slowly warms up. When the pressure and temperature become so high, nuclear reactions start and the matter becomes a star.
Stars range from a mass of 0.08 to 100 (1 mass = the Sun), too small or too big and they are unsustainable.
Now onto the excitement of Orion…
M42 Orion Nebula
It is worth visiting an observatory to view this feature through a telescope. If you have 10 x 50 binoculars you will see quite a few of the features or, at least, you may catch a glimpse of the fuzzy blob with the naked eye. It is an excellent viewing target for January and February.
The Orion Nebulais a major star forming region, with four central stars in the foreground forming the Trapeziumfeature. Recent research has shown stars being formed here. It is 1344 light years away. An interesting project is to make a 3D model of Orion to demonstrate just how far the Nebula is from the main stars of the constellation. The whole area of M42 extends several hundred light years across, covering a much larger area than what is visible from Earth.
Binoculars or a telescope are appropriate for appreciating the Trapezium within the Nebula. (20 x 60 binoculars on a tripod would offer the best view). It is a multiple star system at the heart of the nebula, containing hot young stars. Within the Orion Nebula is a glow of about 30 light years across from ultraviolet radiation from the new stars forming within it.
This region also contains variable stars, ie ones that fluctuate in brightness over time. Visible through binoculars is a dark lane running east from the Trapezium. This feature, known as the Fish’s mouth which separates parts of the Nebula with the Trapezium emerging in the centre. The Horsehead Nebula is a popular image for posters although not really visible except by long exposure telescopes. It lies deep within the Orion nebula region, 1,500 light years from Earth.
As the evenings become darker, so do the mornings and it is helpful to remember that you can also get outside in the morning just before sunrise to enjoy stars and planets and the Moon.
The Winter Hexagon asterism appears in the early evening, giving you time to orientate yourself before becoming overwhelmed by the wealth of stars appearing as the skies darken. Sirius is the very bright star to the south. If you hold this diagram above your ahead, it will show you the orientation of the sky. Hexagon equals 6…or does it?
Sirius (the Dog Star) is the brightest star in the sky 8.7 light years or 80 million million kilometres away in the constellation of Canis major. Extra twinkly due to its immense heat, its name is derived from the Greek for ‘scorching’. It is orbited by a small companion star every 50 years whose own brightness is overshadowed by Sirius.
Procyon (in Canis minor) a binary system, is one of the nearest to our Sun.
Pollux is an old red star near the end of its life, part of Cancer constellation.
Capella is a bright double star in Auriga. Variability is visible as the stars pass in front of each other over a period of 27 years. They are ten times the size of the Sun.
Aldebaran appears part of the Hyades but is only 65 light years away, compared to 150 light years for the main group. It looks like the eye of Taurus.
Rigel in Orion is a blue/white double star, 51,000 times as bright as the Sun. It forms part of a 4 star system.
So, how many stars make up the Winter Hexagon…?
In the realm of the planets there is a real treat in December when Jupiter and Saturn can be seen quite closely together, low but very bright on the southern horizon. This is the closest to each other since 1623!
As October draws to a close, I am delighted to report that I have uploaded the full transcript of my newspaper column that I wrote for the Express and Echo. Also, A stroll through the stars text is complete and I am awaiting more images to include. I have received some positive comments regard the project and am encouraged. I need to remain patient through before I take the project further. Watch this Space!
It is hard to keep up with all the writing tasks…I submit twice weekly to the Exeter Coronavirus Community Diaries via their Facebook page. They seem to like my posts and have asked whether they can use them in an exhibition which is nice. I do also have to do some actual paid Work. And I am working really hard on completing a guide to observing for beginners which will be launched on 6 October 2020 (hopefully!) at St Thomas Library, Exeter.
to work after the Easter break was really bizarre. I just had to remember to switch on the work
laptop upstairs…I did get dressed for work though. Bizarrely.
It still feels good not to have to rush for a bus. I continue to drive to and fro the hospital
to avoid husband catching public transport or anything that might be carried on
it. These are anxious times as it was
announced testing is only being carried out on people who show signs of
symptoms. So, we still don’t know how
much of a risk we are to each other or anyone else. Husband puts his uniform in a pillow case and
straight into the washing machine when he comes home.
Tiredness is a big problem for both of
us. I wake up worrying and having panic
attacks. Husband is just tired. And worried.
I listened to a radio programme about the therapeutic effects of having
contact with nature, even if it is only reading about it. This inspired us to see if any garden centres
were open and, delightedly, we found one that was making deliveries. I phoned an order for some compost and a few
vegetable plants and we are now able to progress our garden plans. We already had quite a few seedlings ready to
be potted on but nothing to pot them on with.
My Dad would be proud.
went out for a local stroll, smiling at a few people who also seemed pleased to
see other faces as they smiled in return.
It is a struggle to find the right exercise. I continue to do some yoga in the mornings as
well as the daily stroll. Housework and
gardening also provide some more exercise.
However, I used to go swimming two or three times a week and really miss
this. My feet prefer a form of exercise
that is non weight bearing as I continue to get fit and lose weight after an
operation three years’ ago to remove arthritis from the left foot. I had only received been issued with some
suitable made to measure shoes which help with balance. It is frustrating not being able to walk on
Dartmoor as I signed up for a sponsored trek that was to take place in August
to raise money for Alzheimer’s Society.
I have neither been able to train nor obtain sponsors!