Cashing in on photons
A short article on an outreach at the Bishop Monkton observatory
Sunday the 22nd of October 2017, a week after the annual auction at the Lamb and Flag, the owners of the Astronomy Evening voucher from 2016 made it to the observatory. It may have taken a year to arrange but that’s nothing to the 2.3 million year old photons hitting our eyes from M31, the Andromeda galaxy.
The author’s own image of M31, the Andromeda galaxy.
This was just one of the sights I was able to show to my guests, Carole, David, Stancey and Olly. What great companions they were too being very patient as I waffled on about the secrets Andromeda gave up to Edwin Hubble and the scientific community in the early 1920s. Showing the attentive audience how to star hop just with their eyes from the great square of Pegasus to a large fuzzy patch overhead was all it needed. Until then most astronomers believed everything we could see was contained within our own galaxy, the Milky Way. How much further from the truth could that have been, as we now know it is merely in our backyard in astronomical terms.
Testing the sky was also on the agenda for the evening and the conditions were such that we could just make out the seven main stars of Ursa Minor with normal vision. That equates to a magnitude 5 sky so not too bad but how much better it could be without all the untamed light around us. Olly, pointing at the Pleiades, remarked that he always thought that was Ursa Minor. An open cluster, number 45 in Messier’s catalogue, known as the Seven Sisters or Subaru in Japan is a very young, close group of hot white/blue stars formed from the same cloud of gas.
The author’s own image of the Pleiades (M45).
We had to crack on though and put to use the short, telescope driving lesson undertaken under red light and over a glass of wine earlier in the kitchen. I wanted to make sure we didn’t miss a chance to view M13, the Great Hercules globular cluster before it sank below the rooftops. It proved a bit of a tough nut to crack because to get the most out of it we had to use a technique called averted vision. David realised that the large fuzzy ball in the eyepiece was made of thousands of stars, bound together by their own gravity like a swarm of bees around a honey pot. These 12 Billion year old stars though take us back to the very start of the Universe.
M13, the Great Hercules globular cluster (Wikipedia commons credit; rawastrodata.com).
It was time to move on to some other deep sky objects so we dipped into the space between Perseus and Cassiopeia to sample the double cluster that is pretty in itself but I wanted my audience to look a bit deeper. Our eyes are poorly equipped compared to cameras but obvious to all is a rich, orange star apparently visiting the cluster of younger members.
Colour tells us so much about a star and so we chased Cygnus the Swan across the Milky Way with both ‘scopes to pinpoint Alberio, the star designating the swan’s head. In the ‘scope everybody detected Alberio as two stars of sharply contrasting colours, an optical double, often described as indigo and gold telling us immediately that they have markedly different surface temperatures and characteristics. Are they gravitationally bound as a binary system? Well the jury is out on that one but current estimates have one third of all stars in the Milky Way to be true binaries.
Getting towards the end of the evening it was time for a couple of more challenging objects. Number 57 in Messier’s catalogue is described as a planetary nebula purely because when viewed in the 18th century it resembled a view of the know planets, small, round (ish) and some colour. These objects have nothing to do with planets but are the result of the after effects of a dying star that has puffed off its last layers of gas leaving a white dwarf at the centre. The gas is energised by the radiation from the star and takes on colours that are determine by its composition, very often the green of triply ionised oxygen.
M57, the Ring nebula (NASA/ESA public domain)
I tried hard to answer and fulfil the questions and requests from my guests and one of the first queries raised before we left the kitchen, was “Can we see any planets?”. Unfortunately it’s pretty poor times in the UK right now for the top targets and will be for some time. However, the two ice giants are in the southern sky so in theory are visible but crikey they are a long way off.
With Olly’s help and whilst the others warmed up in the kitchen we changed to my old Schmidt Cassegrain telescope that has a focal length of 2.3 metres to attempt this feat. This also meant realigning the telescope mount. That took a few minutes but it was then possible to pick out Uranus, which is about 4 Earths wide at a distance of nearly 3 billion miles! It is obviously a disk that has a slight green tinge. We also tried to view Neptune, which is a massive 4.5 billion miles away but the view was slightly obstructed by my roof!
Uranus and Earth comparison (NASA public domain).
Carole kindly remarked about the group’s experience of the evening and her words are below.
“We had been looking forward to this evening ever since we bid for it in the auction. It took a while for us to find a time that was good for everyone and for the skies to be clear and not moonlit. It was well worth the wait and a huge thanks to Chris for offering the event and putting on such an amazing evening.
Having only a very limited knowledge of astronomy, it was great to have Chris enthusiastically explaining to us what we were seeing. He has an array of different telescopes and he patiently set them up in his observatory for us to get the best view of the various stars and planets. Seeing the telescopes and learning about how they are controlled to lock onto coordinates in the sky is fascinating in itself.
Chris has already described above the range of astronomical bodies we focused on in just a couple of hours. Before the evening I don’t think any of us had heard of Messier’s catalogue! There is just so much to observe and it was a treat to see two remote planets. Neptune was a bit naughty trying to hide behind the house chimney but we just about saw it. We also saw Uranus, which was a bonus. Everything else was good to see and the evening was very enjoyable so we hope to see some more at a future date.”