Open University Graduates observe the night sky at Norman Lockyer Observatory, Salcombe Hill Wednesday 13 March 2013

Norman Lockyer Observatory
Salcombe Hill, Sidmouth
The Kensington Dome
(The clock-weights drive the telescope tracking motor)

At 7.15pm on Wednesday 13th March 2013 - when it was much darker than shown in this photo! - a group of ten Open University Graduates gathered for a tour of the Norman Lockyer Observatory at Salcombe Hill above Sidmouth.

Despite occasional showers, the sky was generally very clear. As a result, the temperature on top of the hill was bitterly cold. Everyone had come wrapped up warmly, and some even had the foresight to bring torches. There is special 'red' lighting on the site, which is intended not to interfere with observers' night vision. However, it doesn't help much with normal vision, and it was quite easy to stray off the paths.

The first thing to see was the observatory's subject matter - the night sky. Looking south from the main building, Jupiter was clearly visible in the constellation of Taurus - or rather, in line with Taurus. The Earth was on the opposite side of the Sun from Jupiter in March, and our line of sight to the Sun pointed towards the constellation Aries. (Of course it did - it was March!).

As the Sun was slowly obscured by the Earth's horizon, so was Aries, but Taurus became visible near the horizon as darkness fell. There was Jupiter behind the Sun - and six times as far away - in line with Taurus.  We measure planetary distances in terms of our distance from the sun (150 million kilometers). The distance to Jupiter was therefore about six 'astronomical units' (nearly one billion kilometres).

Aldebaran is big

The nearest star in Taurus is 'Aldebaran' ('The Follower' - Taurus' right 'eye' which 'follows' the Plaedes). Aldebaran is 68  light years from Earth. A light year is roughly sixty three thousand 'astronomical units'. This means that the distance to Aldebaran is over four million astronomical units from Earth (650 million million kilometres).

The other stars of Taurus (those which are visible to the naked eye) are at even greater distances. The most distant is 'Tien Kwan' ('Heaven's Gate' - at the tip of Taurus' right horn, which marks the Chinese celestial asterism, 'Net'). Tien Kwan is 440 light years away - thirty million astronomical units - four million billion kilometres!

Aldebaran is a red giant star about twice the mass of our Sun. It was once like our Sun - the temperature and density of the hydrogen in the core making nuclear fusion possible. The fusion generates high energy radiation which, apart from providing the heat and light of the star, prevents the core from collapsing. However, the nuclear fusion converts hydrogen into helium - decreasing the density of hydrogen. Eventually the fusion slows until it doesn't generate enough radiation to support the core - and the core collapses.

But the collapse generates heat! The core became so hot it made the rest of the star expand. Aldebaran is now 44 times the radius of the sun - with a surface area two thousand times as great. Although it is giving out five hundred times the energy of the sun, it's surface temperature is lower (only 4,000K compared with the Sun's 6,000K). The low temperature is the reason for the 'red' colour.

Tien Kwan is actually two stars orbiting very close together (at a separation of about one astronomical unit!). The smaller star is about the mass of our Sun, and swamped by the light of the bigger star - a blue giant. This has about 11 times the mass of the Sun. The increased mass means more energy at the core, and faster fusion. Tien Kwan is about ten times the radius of the Sun (one hundred times the surface area), but still hotter at the surface - it glows blue where Aldebaran is red. Because of it's rapid energy production, Tien Kwan will collapse at the core in a much shorter time that the sun (millions rather than billions of years).

Betelgeuse is even bigger
(For comparison - Rigel is almost as big as Aldebaran)

To the left of Taurus was 'Orion' ('The Hunter'). Orion's 'bow' is not very easy to see, but his tunic and kilt are clearly defined by six stars. The brightest are Betelgeuse and Rigel (his right shoulder and left knee, respectively) - a red giant and a blue giant, just like Aldebaran and Tien Kwan!

There had already been enough to see to keep an astronomy student going for a year - and the telescopes were yet to come! In the hundred yards from the main building to the 'Kensington' dome it had been possible to contemplate almost inconceivable times and distances.

The Kensington Dome offers a journey back in time - a journey of about a century. There was the beautiful telescope which Norman Lockyer had used for his solar observations at the Kensington Solar Physics Observatory. In order to observe the Sun, Lockyer set up his telescope to project the Sun's image onto a screen - or through a spectroscope. It was by using spectroscopy that he discovered a previously unknown element in the Sun's outer layers - helium.

This helium is not thought to be the product of nuclear fusion at the Sun's core. The current model, based on the observed expansion of the universe, is that, shortly after a 'big bang', protons and neutrons formed. Within the first minutes of the Universe's existence, The neutrons combined with some of the protons to form 'alpha particles' (helium nuclei). About a quarter of the total number of nuclei that resulted were helium. (The rest were hydrogen - and about 1% lithium.) After nearly 400,000 years the nuclei picked up electrons and became atoms, which have existed unchanged ever since - for more than thirteen billion years. As a result, about a quarter of the Sun's mass is made up of these primordial helium atoms.

Kensington Telescope on its
compensatory equatorial mounting

For night-time observation, the telescope is not used to project images. It is safe to look through the eye-piece of the telescope. Observatory volunteer, Vic Papai, had set up the telescope to focus on a very interesting object - Jupiter. Each visitor, bundled in scarves and overcoats, took a turn to peer through the lens. Initially, most people saw nothing. Then, when they discovered how to aline their pupil with the axis of the telescope, the planet came into view.

Initially the image just seemed to be a white disc. As the eye adjusted, the familiar bands and great red spot became visible. The clarity of the image would vary with the turbulence in the atmosphere. However, the planet remained dead-centre in the field of view. This was because Vic had set the clockwork motor running, which makes the telescope rotate on its mounting at the same rate as the Earth - but in the opposite direction. This is very convenient, but does mean the eye-piece may move out of reach during observation. To solve this problem the dome has an essential extra piece of equipment - a stepladder.

Jupiter and the Galilean Moons

When the image was particularly clear, something new became visible - three tiny pin-pricks of light on either side of Jupiter. These were the Galilean Moons. There are actually four, but one was out of sight behind the planet. When Galileo Galilei first observed these moons, four centuries ago, he was so fascinated he watched them night after night through his telescope. He soon deduced from their changing positions that they were orbiting Jupiter - reinforcing the idea that not everything orbits the Earth.

The McClean Telescope
set up for solar observation

Vic then took us to the McClean dome, which houses the even larger McClean telescope. This is also a refracting telescope (collecting light with a lens). The lens is a foot wide, compared with the Kensington's ten inches. The telescope was originally commissioned by Frank McClean, a wealthy entrepeneur and keen amateur astronomer. His son Francis McClean supported Norman Lockyer in building his observatory at Salcomble hill in 1912, and donated the telescope.

The telescope was made in Dublin by Sir Howard Grubb in 1894. This is the same model as the one used for the International Astrographic Survey of 1896. With an eye for a bargain Frank McClean had ordered a second identical telescope - special offer, half price. After his father's death, Francis gave one to Norman Lockyer, and one to the Radcliffe Pretoria Observatory in South Africa.

Fireball over Chebarkul 15th February 2013

Having completed his fascinating historical and astronomical tour, Vic Papai handed over to David Strange who was in charge of the 'Solar, Planetary and Meteor Detection' ('SPAM') system. Meteors were very much in the news at the time. A large chunk of something had burned up and exploded in the atmosphere over the Russian town of Chebarkul in the Urals on Friday 15th February.

Fragments of the meteoroid (called 'meteorites' once they hit the ground) have been found. The heaviest piece so far found weighs about two kilogrammes. Professor Viktor Grokhovsky, of the Institute of Physics and Technology, at the Ural Federal University, has led a team who analysed the fragments and estimate that the original meteoroid was about seventeen metres across and weighed about ten thousand tonnes.

2kg fragment of the Chebarkul meteorite

Meteroids are understood to form in the same way as the planets, by the conglomeration of dust orbiting in the Sun's accretion disc. A lot of the dust contains iron. Iron is the final product of nuclear fusion in very massive stars. To make heavier elements requires putting energy in - so iron accumulates in the core of a star until fusion stops and the star's core collapses finally and catastrophically - causing a supernova expolsion of the outer part of the star. The explosion is so powerful it ejects iron into the interstellar medium, and also creates small amounts of heavier elements. This is thought to be the source of all the heavy elements in our solar system.

An iron meteorite -
cut to show the metal structure

If the dust collects into a fair-sized 'planetesimal', the collisions involved will have made it so hot that it is molten. The iron collects in the centre. Once it cools and solidifies, a further big impact can shatter the body creating two kinds of meteoroid - 'iron' and 'stone'. Grokhovsky has established that the Chebarkul meteorite is of the stony kind - a 'chondrite'. A sixteen metre wide hole in the ice of Lake Chebarkul implies that there is a further one-hundred-kilogramme lump of stony chondrite on the lake bed.

Professor Peter Brown of the 'Western Meteor Physics Group' at the University of Western Ontario (London, Ontario) has analysed atmospheric data collected during the fall. He concurs with Grokhovsky's estimate of the meteoroid's size, and calculates that it originated in the 'Asteroid Belt' - a ring of rocky and iron debris orbiting between the orbits of Mars and Jupiter.

SPAM collates meteor data
by detector and amplitude

David Strange handed round an iron meteorite to illustrate the kind of material involved. (The composition of the Chebarkul meteorite had not been determined at that time.) He also introduced the graduates to the 'S.P.A.M.' meteor detection system. This collates radar data from national satellite detection systems and displays the information on a three dimensional graph which is updated in real-time.

Time is represented by the diagonal direction from top left to bottom right - so the bottom right surface represents the present moment. The two axes of the front slice are initially confusing. Frequency is represented horizontally - different countries use different radar frequencies to detect meteors. The vertical axis represents amplitude - the strength of the 'echo' from the meteoroid, which gives an indication of its size.

Longer traces imply less transient objects - including aircraft. There is a continuous trace representing the moon. Spikes result from meteor impacts. As one watches, a series of spikes appear, some much larger than the others. David explained that these meteors were created by small particles - little more than dust grains. Their velocity relative to the Earth may be very high. In extreme cases, when they are travelling in the opposite direction to the Earth, their relative velocity could be up to seventy kilometres per second straight towards us.

The 'Perseids' meteor shower in July

When the particles enter the 'mesosphere', about one hundred kilometres above the Earth's surface, friction with the air heats them until they burn up. The resulting streak of light in the sky is the familiar 'falling star'. Larger objects may explode when they get hot enough and continue as several separate meteors.

At certain times of the year the Earth passes through the orbital path of comets. Each orbit is strewn with material boiled off the comet by the Sun. The Earth ploughs into each cometary orbit in the same direction each year - heading directly towards the same constellation in the sky. In July, for example, the Earth is moving directly towards the constellation of Perseus when it crosses the path of comet Swift-Tuttle. The resulting meteors all appear to originate in Perseus and radiate outwards in all directions. These meteors are called 'Perseids', after the children of Perseus and Andromeda in Greek mythology.

A time exposure of the Andromeda Galaxy

On the way back to the main building the visitors' eyes, now well acclimated to the night sky, could even pick up the most distant visible object - the Andromeda Galaxy. A small white smudge is visible, just 'below' the W of Cassiopeia - and close to the constellation of Andromeda. If one observes closely on a dark night, the distinctive shape slowly emerges from the gloom - an ethereal fried egg. This is a spiral galaxy, similar to our own Milky Way, seen nearly edge on.

The 'Local Group' of galaxies
relative sizes and positions

M31 = Andromeda,
M33 = Triangulum

The Milky Way and Andromeda galaxies are each roughly one hundred thousand light years in diameter - and are separated by a distance of  about two and a half million light years. In astronomical terms this is significant. Relative to their size, they are very close together. The Milky Way and Andromeda galaxies are in fact part of a 'cluster' of galaxies, called the 'Local Group'. This group includes all the satellite galaxies of the two main spirals, fifty four in all. Observers in the Southern Hemisphere can also see our closest neighbour, the Large Megellanic Cloud which is only 160 thousand light years away.

From the cold and exciting darkness of the Salcombe hilltop, with its wealth of fascinating astronomical opportunities, the intrepid group returned to the warmth and brightness of the Donald Barber Lecture Theatre in the main building. Raising its own funds, the Society built this facility in 2006, in memory of Donald Barber, who was Director of the Observatory from 1936 to 1963.

Donald Barber Lecture Theatre

Here we were treated to another voyage of discovery. The Observatory Society Chairman, Alan Green, gave a brief talk on the subject of astronomy, ancient and modern. His fascinating slide show (or rather 'Powerpoint presentation') kept everyone's attention for a cosy half hour. Alan also told us all about the many different groups who meet at the observatory, and the interesting work they do - radio, meteorology (that's weather, not meteors!), and history of science are all covered, as well as study of the coast and countryside around Salcombe Hill.

Needless to say, Alan concentrated on the Observers Group. (There are an Adult Observers Group, and a Young Observers Group.) Observers are divided between 'Astronomy' and 'Solar, Planetary & Meteor', according to what they want to study. However, all meet together every Friday at 7.30pm. There are enough small astronomical telescopes for everyone to set up outside and have fun observing the universe.

"What's that light in the sky?"

After seeing the domes is odd to think that a telescope can simply be set up on the grass outside. The whole site is good for observing - because it is relatively free for 'light pollution'. The domes are only really needed to protect the bigger telescopes - when it rains!  When it does rain, there is a fully equipped planetarium in the main building - for lectures and demonstrations about observing, and the positions of the stars and planets in the sky.

Every month there is a Society Lecture in the Donald Barber Lecture Theatre - usually on a Monday night. There are also open days, astronomy courses open to the public, and special astronomy days - either to do with astronomy generally, or at any time when there is a significant astronomical event in the night (or daytime) sky.

The 2012 Transit of Venus
recorded safely through clouds
by Melbourne film-maker
Michael Franklin
using his
Canon EOS 60D

For example, on 8th June 2004, the observatory was crowded with people who came to see the 'transit of Venus', which is the rare occasion when the black disc of Venus can be seen between the Earth and the Sun. Norman Lockyer's telescopes were installed for just this purpose - to project the Sun's image for safe viewing.

There are only two transits each century, eight years apart. The transit in 2012 was sadly when the Sun was not visible from Salcombe - making the 2004 event unique for this generation in Devon.

Wednesday 13th March was a truly glorious evening out for the Open University Graduates.

Many thanks to Ann Reed for arranging the visit

- and to Vic Papai, David Strange, and Alan Green for such a memorable event.


To find out more about the Norman Lockyer Observatory Society, and maybe get involved, contact:

01395 579941 (not always staffed!)

or take a look at the Norman Lockyer Observatory Society website:

www.normanlockyer.com