This week presents an opportunity to enjoy a meteor shower. Thursday night (12th August) around 1am will be the peak of this shower although they are visible for a few nights either side, weather permitting of course. Thursday night is looking clear. The Perseid meteor shower is one of the Regular Meteor Showers, and which are visible either side of the main date in those quiet hours before dawn (it is advisable to check the press for up-to-date information and weather before embarking on a session. You may come across the Zenithal Hourly Rate, this is just the term given to the number of meteors likely to be seen directly overhead. Did I mention it might be a good idea to use a sun lounger? You will be looking up at a wide area of the night sky so lying down on something dry and comfortable is a good idea. The Perseids are an enjoyable holiday treat as, if you are fortunate enough to be on holiday, the late night will be less of an issue and the nights are less cold at this time of year. The meteor shower comes from the tail of Comet Swift-Tuttle and emanates from the constellation of Perseus (referred to astronomically as the radiant). This year (2021) the moon will not be visible, so there will be no light pollution from that source and the Zenithal Hourly Rate is said to be around 30-60 meteors (this is the amount of meteors likely to seen overhead). I treasure my memory of a family holiday a few years’ ago when we set the alarm for 3am to enjoy the Perseids and were rewarded by the sight of quite a few trails. And the faces on the security guys as they wondered whether we were ok. Perhaps we did look a bit odd in our dressing gowns wandering around a holiday park at night but, hey, it was worth it, and we spread meteor watching fever onto those men too.
With many people taking a summer break during August, there is an excellent opportunity to have a late night or a broken night, while not getting too cold. I am referring to the annual Perseid meteor shower…assuming it is a clear night of course. This year, the Perseids are due to appear during the nights of 11-13 August. Although the shower originates in the constellation of Perseus, the meteors appear in all parts of the sky. The best time is after midnight, more towards the hours before dawn. One year I got up at 3am, having gone to bed early, and was rewarded by the sight of the meteors. This year, the moon will have set in the early evening during its waxing crescent stage, which means the skies will be dark. It is also possible to see them a night or so either side of the main dates. Indeed, I photographed the supermoon the day before it was at its peak – which was just as well as the evening of the main event was cloudy! Meteor showers occur every year as the Earth passes through the tail of long gone comets. Comets are a huge topic though.
This month sees spring turn to summer, during the early hours of Monday 21 June. It is when the sun is in its most northern position relative to Earth. Our northern hemisphere is pointing towards the sun, while the southern hemisphere begins its winter season. The north pole now gets its share of daylight, having emerged from round the clock darkness of winter. It is quite a feeling to be out and about in daylight at midnight! Stonehenge is well known of course for being in line with such astronomical events and recently I spent a few days in Pembrokeshire where I was fortunate enough to walk around the area from where the bluestones originated for Stonehenge. It would have taken 150 days to pull a bluestone to Wiltshire on a sled of some sort. The more recent druid type rituals at Stonehenge are not deemed to be the original purpose of the henge monument, having only occurred relatively recently in its history. An activity you can do is to photograph on 21 June, a tree with a very short shadow and then take subsequent photos a month apart to see the effect of the movement of the Earth away from the sun. It is interesting to view the photographs in a sequence to appreciate just how much movement there is.
But I digress, the summer solstice varies slightly by a day or so year on year due to the Earth’s rotation around the sun. Each summer solstice is around 6 hours later than the previous year and in a leap year, the solstice jumps backwards by a day. Remember, it takes 365 and a quarter days for the Earth to go around the sun, which is why we have an extra day every four years.
I am often asked why the sea is so cold in the summer…I went swimming in November and found the water to be much more pleasant than in August. Likewise, those people who jump into the sea on Boxing Day are less brave than those who do so at Easter when the sea has cooled down. The sea warms up with the lengthening days and takes a while to cool, hence warmer in December.
Another fun activity to enjoy during the, hopefully, warm summer days is to make a solar cooker. Full instructions are on my website, but briefly, you need a large piece of cardboard, plenty of kitchen foil and a lot of patience. No, it is quite simple to make, you are making a concave shape which will absorb a lot of heat from the sun as it is concentrated to a point in which you can put a small plate of water or a piece of bacon. And wait while the sun heats them. Be very careful not to put your hand in the line of fire so to speak. Nor look at the sun directly.
A less obvious activity to do during this somewhat fallow time for observing, is to look at a Planisphere or star atlas and familiarize yourself with the positions of the constellations during the autumn and winter so you are ready to go out in the dark, armed with the knowledge of where to look and what to look for. My book, “A stroll amongst the stars” takes you through the main stars from September to August in line with the typical observing year. At the Observatory we particularly enjoy September and October when the nights are longer but not too chilly. And take a break in July and August to enjoy the longer days. Now is the time to download free computer programmes such as Stellarium, buy my book, or take astronomy books out of the library, and sit back and learn about the subject in more detail ready for active viewing.
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!).
May I wish you all a Happy Easter.
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!
This is a gentle guide to observable astronomy and designed to whet your appetite for enjoying the darker skies.
A stroll through the stars…coming soon. To order, please use the contact form on the website. Just £10 for a gentle guide to observational astronomy.
I was delighted to win Prima magazine’s monthly short story magazine and my story is in the July 2020 issue. It is so exciting and encouraging.
I have not been putting posts on here as I have been posting twice a week to the Exeter Coronavirus Diaries Facebook page. Those posts will be put in a book or exhibition at a suitable time.