Alan Willison, chairman of Hertford Astronomy Group, offers his tips on sky-gazing in his monthly column on how to get started in astronomy.
Did you get a telescope for Christmas? If you did, then here are some things that you can look for. Even if you didn’t there are many things that you look for without one.
We’ll break down this edition into four parts:
- Constellations
- Planets
- Stars
- Deep Space Object(s)
Constellations
First of all, let’s define a constellation. It is a group of stars that appear to make a shape in the sky and that shape is attributed a name often related to some mythical story but not always.
There are 88 constellations in all. The stars themselves are not usually related to each other but from the Earth make up the pattern that we see.
This month’s constellation is Orion the hunter, who can be seen kneeling in the southern sky holding up his shield to defend himself from the charging bull Taurus.
The seven stars that make up the familiar shape are all in the top 70 of the brightest stars visible to the naked eye. The three that make up a line in the centre are known as Orion’s Belt and are 1,200 light years away from us.
Just imagine that if any of those three stars in the belt had planets with life on them and they had received a telescope that could see Earth they might be able to see Charlemagne being crowned as emperor of the Romans or King Alfred defeating the Danes in the Battle of Edington.
Planets
This is a great time to look at the planets.
All of them are technically visible for a while, although you will need your telescope, some accurate pointing and a touch of good luck to be able to see Uranus and Neptune.
Download Stellarium to your computer, tablet or smart phone and that will show you where to look.
Stars
Staying with Orion, there are two very bright stars marking his shoulder and foot. These are Betelgeuse and Rigel respectively.
Betelgeuse is a huge star and much closer than the stars in the belt. Betelgeuse is about 500 light years away from us and, if it was located where our Sun is, it would engulf Mercury, Venus, Earth and Mars – and then a bit more!
Not only is it big but it is also bright, what we call luminous. It is what is known as a red supergiant.
The red is noticeable especially if you compare it to the other very bright star Rigel, which is diametrically opposite Betelgeuse.
Rigel is also a supergiant but this time it is a blue supergiant. It is about 850 light years away from us.
It is brighter than Betelgeuse, even though it is further away, and the blue colour tells us that it is hotter than Betelgeuse – just think of heating up a piece of iron and you may be aware that white hot is hotter than red hot and it is the same with stars.
What is fascinating about these two stars is that they are both coming to the end of their lives which will result in what we know as a supernova.
As the hydrogen that fuels a star runs out the star collapses upon itself and then explodes dramatically. A dense core is left – a neutron star – and this illuminates the debris created from the explosion.
The explosions are likely to be seen from the Earth even in daylight, and may last anything from a few days to a few months. Fortunately, both stars are sufficiently far enough away from our solar system as to pose no threat to us.
They are due to explode anytime in the next million years or, indeed, might have already happened and we are just waiting for that light to reach us.
We have a great photo of what that might look like – see photo of the month below.
Deep space objects
First of all, what is a deep space object (DSO)? It is generally considered that DSOs are objects outside our solar system that are not individual stars.
This includes nebulae, star clusters and galaxies. A nebula (plural nebulae) is a cloud of gas and dust.
A star cluster is a group of stars that are of about the same age and are gravitationally bound to each other for a while.
A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity.
Back to Orion and there are nebulae there to be found. These huge areas of gas and dust are where new stars are born and are known as stellar nurseries.
About midway between his belt and his feet there is a misty patch known as the great Orion nebula. We have published pictures and descriptions of that before, so let’s look at another one – the Horsehead Nebula.
Situated just below the easternmost star of Orion’s Belt this cloud of dust and gas is illuminated by a neutron star.
The neutron star is all that is left after the explosion and subsequent collapse of material. It is easy to see where it gets its name from with that large dark cloud in its midst.
This is one for the astro-photographer, so don’t be disappointed that you can’t quite make out the shape looking through your telescope.
Photo of the Month
It is of the Crab Nebula, which is the remnant of a supernova that occurred in the year 1054 and is visible today – but you will need a telescope as it has faded over the years.
It is situated at the tip of Taurus’s lower horn.
The photo was taken by Martin Weston from his garden in Wheathampstead.
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