This 22.5 inch reflector carried out important work on supernovae in the 1970′s and 80′s, operated at Burwash in Sussex, by it’s designer and builder Alan Young.

It then lay dismantled and unused for many years, before coming into the hands of Cranbrook School. Volunteers at their astronomy society have worked over the last couple of years to restore the telescope to operation.

The restoration project is now reaching the final stages.

Here’s a close-up picture of the recently fitted Crayford focusser with a custom motordrive. The arrangement will permit careful adjustment of the focus, from the observatory floor level. This is essential…

As you can see here, from this picture of the Mintron camera being fitted to the focusser. It is many feet up and requires an access tower to reach safely.

In the bottom picture, the declination axis drive is being adjusted.

The telescope is expected to be fully operational soon.

However, it is rather humbling to realise that there are billions of stars in the universe. And even worse, our Sun is an unremarkable star.

There are many stars that are bigger than our Sun and many are smaller. Some are older, others younger.

We also now know, through modern detection methods, that other stars have their own planets in orbit around them.

So what is a star and how does it come into being?

What Is A Star?

A star is just a large ball of gas, nothing much more. For all its apparent fury and violent energy generation, it is just gas.

The gas is mainly hydrogen and helium. If you have ever learned about the Periodic Table, you will know that these are the two simplest elements, with an atomic number of one and two, respectively.

The heat and light generated comes from nuclear fusion reaction, in which hydrogen atoms are combined to form helium, releasing enormous amounts of energy.

The star has so much mass and therefore so much gravitational force acting inwards towards its centre, that fusion processes keep going for millions of years, generating the heat and light that we are familiar with.

How Do Stars Form?

With telescopes, we can observe regions in our galaxy where there are vast clouds of gas.

It is believed that stars form in these clouds of gas, as it begins to coalesce. So these gas clouds are “stellar birthplaces”.

As the gas coalesces, denser clouds form and gravity increases. This leads in turn, to still greater density. The forming star begins to rotate.

Eventually, if there is enough material, temperature and pressure increase to the point where nuclear fusion begins and energy generation starts in earnest.

A “star is born”.

The star then settles into a long period of equilibrium, during which the energy generation that increases pressure and forces material outwards, is just balanced by the forces of gravity holding the material into a sphere.

The more massive the star at this point of equilibrium, the brighter it will be.

This is what we observe in the sky. Stars come in a range of sizes and brightnesses.

How Do Stars End?

Eventually, the hydrogen fuel for nuclear fusion begins to run out and the star generates less energy and cools.

What happens next, depends on how massive the star is.

With stars of low and medium mass like our Sun, the outer layers will expand in size and cool, forming a “Red Giant” star. This will be many times larger in diameter than before.

Eventually the outer layers will dissipate and the central core collapse into a “white dwarf” star.

Alternatively, for more massive stars, the outer layers may blow off to shroud the star in a nebula of gas, called a “planetary nebula”. A good example of a planetary nebula is M57 (the Ring Nebula), in the constellation of Lyra.

Much more massive stars may end catastrophically , with the star exploding as a “supernova“.

Part of this process involves the core of the star collapsing into a “neutron star” or a spinning, flashing “pulsar”.

An example is M1, the Crab Nebula in Taurus. This is the remainder of a supernova seen in the year 1054 and it has a pulsar at its centre.

In the case of very massive supernovae the core may collapse to form an incredibly dense “black hole”, from which no light or other radiation can escape.

A “Guest Star” in astronomy is a star that just suddenly appears in the sky, in a location where there was not one before.

To be more accurate, the star WAS there before, but it was too faint for us to see. So it appears, not because it has been created, but because it suddenly becomes much brighter and we are able to observe it.

The period of massively increased brightness seems to last for 1-2 years, usually.

Why Are They Called “Guest Stars”?

These phenomenon are called guest stars because this is a literal translation of the Chinese Mandarin word that was used for them.

Why the Chinese? Well this is because astronomers in China over the last 2000 years, have been very good at observing and more importantly, recording in documents, when these sorts of happenings have occured.

There are fabulous observational archives in China which are only now being translated, so there may be a lot more historical knowledge to come over future years.

In Europe and elsewhere, guest star events have only been recorded in the last few hundred years.

What Causes A Star To Suddenly Get Brighter?

Guest stars are basically star explosions. There are two types:
a) Supernovae – when the star completely explodes and leaves nothing but dust and debris, and;
b) Novae – when an outer layer of the star, somehow “blows-off” with a great release of energy, but the remainder of the star survives.

It has been known for decades that the larger stars (perhaps those more than about eight times as massive as our Sun), can behave in this way.

Astronomers are now trying hard to classify stars into various types and so understand what circumstances give rise to nova and supernova events.

How Easy Are They To See?

They can be extremely easy to see, even with the unaided eye and sometimes even in daylight! However, for a supernova to be this bright, it has to be within our own galaxy and so, relatively close.

There has not been a guest star in our galaxy for over 400 years.

The last exploding star in our galaxy was the so-called “Kepler star” of 1604. This was in the constellation Ophiuchus and was as bright as the planet Venus appears.

Kepler did not discover this supernova, but he was an eminent professional astronomer at the time and he carried out accurate measurements of it.

Find a catalogue of known guest stars in our galaxy here Historic Catalogue Of Supernovae

Many, many star explosions have been observed in OTHER galaxies, especially in the last few years.

UK amateur astronomers deserve a mention here.

A few individuals have become particularly good at discovering supernova events in other galaxies, with over 200 found from UK since 1996. But these extra-galactic star explosions are of course much further away and require good telescopes to observe them.

Are Guest Stars Useful?

The short answer is, Yes.

As well as being dramatic, mind-boggling events that get people interested in astronomy, these supernova events are becoming increasingly useful to professional astronomers. They are making use of supernovae to estimate how far away distance galaxies are from the Earth, and so better understand the structure of the Universe.

If a supernova occurs in our own galaxy the “Milky Way”, it can be highly visible in our sky, sometimes even during daylight.

There have been a number of well-known, highly visible supernova events in the history of astronomy, although there has not been one for 400 years.

When they have occured, they have had great influence on astronomers and astronomical thinking, at that time.

Here is a brief catalogue of known, bright supernovae.

Year AD1006 in the constellation of Lupus

This would have been too low in the sky for the UK, but it was observed and recorded in China and also at St Gallen in Switzerland.

It was very bright – nearly as bright as the Moon – and lasted for over two years. The remnant is not visible optically today, but is detectable as the radio-wave source SN1006.

Year AD1054 in the constellation of Taurus

The remnant is visible today as the Crab Nebula. The exploding star reached magnitude -4 (as bright as Venus appears) and lasted for 21 months.

It was extensively observed and recorded in China, but strangely, there is NO confirmed record in Europe.

We may ask, why was this event ignored? Astronomers surely must have seen it?

It is suggested that to blame, could be the dominant doctrine on the perfection and unchanging nature of the universe, as decreed by Aristotle and Ptolemy a thousand years before. Astronomers were not willing to record what they saw, because it was clear evidence that the universe was not as was believed and they feared upsetting the authorities.

Year 1572 in the constellation of Cassiopeia

This was the supernova that was famously observed and measured by Tycho Brahe. It made his reputation as a great astronomer. It also touched him personally, writing that it was “a special creation of God”. Tycho’s personal notes still exist in a museum in Copenhagen.

It was as bright as Venus (about mag-4), but by May 1573 has faded to magnitude 2. Today, its remnants may be found in the optical and radio spectra.

Year 1604 in the constellation of Ophiuchus

This supernova is often known as the “Kepler Star”, not because Kepler discovered it, but because he observed, measured and recorded it as part of his official work.

It was like as bright as Venus, like the one of 1572, just 32 years before. But particularly striking, would have been its proximity to both Jupiter and Saturn, at that time. A remarkable sight!

When will the next “guest star” appear in our galaxy?

Who knows? Certainly not me. But 400 years have passed since the last nearby star explosion.

And we have recently detected hundreds of supernovae in other galaxies.

So perhaps it will not be too long to wait?