There’s Orion at the bottom of our garden…
I have just completed a great series of 4 Planetarium Night Classes on The Universe for Beginners at Glasgow Science Centre . The Planetarium is great, with a 15 metre dome and a spectacular state-of-the-art fulldome digital projection system – it has super, laid-back comfy seats too. Each night started with the house lights dimming as our eyes got dark-adapted and a fabulous view of the night sky outside, as if the sky was not overcast for a change. And as if there was no light pollution, in fact so many stars were visible that the few we are normally familiar with almost get ‘lost in space’. But our stalwart winter companion, Orion, was always recognisable, and centre stage at the start of each evening.
Which reminded me of our back garden, in Cathcart, where Orion is always very welcome – particularly at this time of year. So I was moved to take another ‘happy snap’ of him with my Canon EOS 500D camera – but mounted on my telescope’s equatorial mount so that I could take long exposures with no star trail problems. This time actually I only took one, (remember – astrophotography the easy way) and for a change I remembered to take a matching dark frame with the lens covered. Then I used the free Deep Sky Stacker application to subtract the dark frame from the light one to reduce ‘noise’ introduced by the camera on long exposures with high ISO settings. Here is the result, you can see Aldebaran, in Taurus and top right, too:
File name : _MG_0481.CR2
File size : 18453932 Bytes
Image size : 4752 x 3168
Camera make : Canon
Camera model : Canon EOS 500D
Image timestamp : 2017:03:01 20:15:14
Exposure time : 20 s
Aperture : F8
Focal length : 28.0 mm
ISO speed : 1600
Exposure mode : Manual
Copyright : Dalriada Downshift
Last night I went back to Glasgow Science Centre to hear Professor Jocelyn Bell Burnell give a David Elder Lecture, on Cosmic Fireworks. She began by explaining some disadvantages of long exposure astrophotography! Even the Hubble Space Telescope is not immune. It produced a famous image of the Hubble Deep Field , a tiny area of the celestial sphere only 15 arcminutes across – a two-millionth of our sky.
The first Deep Field, the Hubble Deep Field North (HDF-N), was observed over 10 consecutive days during Christmas 1995. The resulting image consisted of 342 separate exposures, with a total exposure time of more than 100 hours, compared with typical Hubble exposures of a few hours. The observed region of sky in Ursa Major was carefully selected to be as empty as possible so that Hubble would look far beyond the stars of our own Milky Way and out past nearby galaxies.
The results were astonishing! Almost 3000 galaxies were seen in the image.
BUT, as Jocelyn Bell pointed out, long exposures miss some information by accumulating observations over time. If you took a very long exposure of a traffic light you would record all three , red, amber and green, aspects but miss the fact that each is individually illuminated for relatively short periods of time. Cue Time Domain Astronomy, an exciting new field which targets The Transient Universe. Jocelyn Bell is a Professorial Fellow in Physics at Mansfield College, Oxford University and she introduced the topic of Fast Radio Bursts (FRBs) which are radio emissions that appear temporarily and randomly, making them not only hard to find, but also hard to study. Jocelyn Bell is credited with the discovery of pulsars, as a radio astronomy graduate student in 1967 (for which her supervisor won the NoBell prize !) but FRBs are even more difficult to detect. One of the most interesting properties of FRBs is that their dispersive delay implies that they have travelled through much more plasma than is contained within the limits of our galaxy. They are therefore suspected to be extragalactic. (see The future for radio astronomy). Most likely candidates include Supernovae, and maybe Blitzars, hypothetical astronomical objects in which a spinning pulsar rapidly collapses into a black hole. I don’t pretend to understand all this but I enjoyed not understanding it – shades of Socrates.
Meantime, back at Jupiter a much more leisurely dynamic process was in progress – one of its Galilean moons, Ganymede, crossed in front, preceded by its shadow. But beginning way too low in the East for me, you will have to make do with this Cartes du Ciel screenshot: