Astronomy Course

The Astronomy Course materials for the Open University's S194 course have arrived. Flipping through the book it looks like one of those courses where you have to remember lots of facts, and also have to do practical things too.

The course starts on the 12th, so I'll be spending time getting the resources lined up and in readable forms. If I can get them all into one convenient OneNote file that I can access from Laptop, PC and elsewhere then I can study in a 'portable' manner.

I'll find a nice little cloud to put them all on, or dump it all in SkyDrive.

Stacking Images

In other news, I'm currently working out how to stack astronomical images to improve piture quality and resolution. Apparently sticking a web-cam on to my telescope, taking a large sequence of images and sticking them in Registax is the way forward for this.


Tuesday night the sky was clear, and by 10.30-ish Jupiter was visible well above the house opposite. I took the telescope out into the front garden, and attached the recently-purchased 5mm eyepiece and lunar filter. The eyepiece gave a more magnified, but still reasonably sharp view of Jupiter, and the eyepiece cut out most of the glare so that details were viewable.

I could see both the main northern and southern ‘belts’ of cloud, though couldn’t quite make out the red spot. Maybe it was round the back or something. Since the view was a higher magnification, the ‘cone’ of sky was narrower, and so Jupiter was moving quite swiftly. It also meant that the slightest vibration would send the view out of kilter. This brought home to me the importance of having a good, solid mount and nice tight screws!

Another thing that I hadn’t fully appreciated was the effect of the atmosphere. You know those images you see in nature programmes and documentaries of the large, red setting Sun wobbling down past the horizon? And it’s shimmering in the heat haze? Well, I found that this effect was quite pronounced whilst viewing Jupiter, and that the image would stir, wobble and shift due to peturbations in the atmosphere. It’s a bit like viewing something through glycerine.


Last night a very bright star was risng over a neighbour’s house out the front, so I wandered outside with the telescope (much swearing) and set it up outside.

The telescope came with three different eyepieces. There was one marked ’20mm’, one marked ’10mm’ and one called ‘Barlow’ which doubles the magnification of one of the other two.

The numbers in millimetres are the focal lengths of the eyepieces, and different focal lengths give different magnifications. You can work out the magnification using a small formula:

magnification = telescope focal length in mm ÷ eyepiece focal length in mm

My telescope has a focal length of 900mm, and so the 10mm eyepiece gives about 90x magnification, and the 20mm eyepiece gives 45x magnification (i.e. a smaller image and bigger area of sky, so useful for ‘wider’ objects).

With the 10mm eyepiece, and the prevailing atmospheric conditions, Jupiter was a very bright disk the size of a lentil, with a line of small dots either side of it – Jupiter’s moons. It was very bright indeed, so bright it was difficult to make out much detail, but I saw a couple of faint stripes of the cloud belts.

It’s an awesome feeling to see an actual planet, in real life, rather than just watching it on TV. A bit like bumping into Stephen Fry or Richard Ayoade in the street or something. Or maybe it’s a bit like having a ‘free entry’ ticket to the wider universe.

You can add filters to the telescope. Whereas in my last post on the topic I mentioned that lack of light makes things look a bit grey and faint, with bright objects like planets it will sometimes pay to filter out some of the light in order to be able to see detail properly.

A couple of weeks ago I found that this is expecially true of the full moon: when photographing it I had to use similar settings to those I would use during the day in order to get any detail. For astronomers, one cannot adjust the ISO or shutter speed of the telescope (the hole is always open), so one uses filters to block out the light.

You can purchase Moon Filters, as well as filters designed for specific planets (Venus filters etc.) and even light-pollution filters.

Back to the eyepieces and magnifications. Using only the formula above, one would have quite reasonably thought that one could just purchase eyepieces with progressively shorter focal lengths in order to get progressively higher magnifications. This is partially true, however the image will start to deteriorate after a certain point, getting grainier and crappier as you go on.

Each telescope has a ‘maximum effective power’, above which images start to look pretty dreadful (assuming you can see them at all). This is worked out from the aperture (‘width of hole’) of the telescope, doubling it by two-and-a-bit. You can work out a conservative estimate using the following formula:

maximum effective power of telescope = telescope aperture in mm × 2~2.5

So I could probably get a reasonable 260x magnification, perhaps as much as 320x at a pinch. Therefore a 2mm eyepiece, yielding a 450x magnification would be a pointless expense, but a 5mm (yielding 180x) may be worth a punt, tegether with a neutral density moon filter…

Years ago, if anyone ever told me I’d consider spending £30-odd to make a white dot look a bit bigger I’d’ve laughed in their face.


Finally, after waiting for three days, the skies were clear enough this evening to make use of my new telescope. The frustrating grey-brown blanket of cloud finally dispersed, and so I set about getting the thing out of my living room, out of the door and under the stars where it belonged.

I thought getting my bike out of the hallway was awkward. The telescope apparatus consists of a tripod, an ‘Equatorial Mount’ and the tube+mirror bit (which probably has a more technical name), and was a complete pig to assemble. It had other qualities in common with a pig: its weight and general reluctance to be moved to name but two. It also has lots of things that stick out as well, and having already set it up and balanced everything I was unwilling to take it to bits again and reassemble it outside in the dark.

Having got it outside, I proceeded to calibrate the little wheels and things. First thing to sort out was the ‘Red Dot finder’, a sort of laser-pointing device that projects a tiny red dot onto an eyepiece, allowing you to ‘aim’ the observation tube apparatus. These both have to be pointing in the same direction otherwise there’s little point in having it, and if you don’t have it you’ll find it impossible to find anything out there. Space is rather large, and is even bigger when you magnify it a hundred times or so.

I used a distant chimney for this, because it wasn’t moving.

This done, I fished out a small spirit level, recently purchased from Clas Ohlson for £2.29, and ensured that the tripod itself was flat.

Next up, the Latitude adjustment. I had to ensure that the Equatorial Mount pointed towards Polaris. I roughly aligned the apparatus North using a recently-purchased-from-Clas-Ohlson compass (£4.99), aimed the red dot at Polaris, and started adjusting the Latitude wheel. All was good.

These two jobs done, I had to learn how to move the telescope. The weird thing is that it doesn’t, as one would expect, tip in a simple up and down motion, and rotate left and right (well, unless something’s come loose). Once everything had been aligned, one control would alter the ‘Declination’ (a bit like Latitude) and the other would adjust the ‘Right Ascension’ (akin to Longitude) of the scope. The idea is that as the Earth turns, the stars seem to move, and so to keep up with them you only need to fiddle with the Right Ascension control.

OK, took me a while. I still wasn’t seeing much due to messing about with my torch, and the light coming out of the back door. I switched to using my rear bike light for illumination, and taped a binliner over the back door windows. A few minutes later I went back, and pointed it at Cassiopeia.

Wow, there were hundreds, thousands of tiny stars! Despite being within about a mile of the city centre! This was amazing. I started to nose round the sky using an old star chart.

I found the Andromeda Galaxy! It was a pretty damned big, yet faint grey ‘splodge’ amidst the stars. I actually recognised it from my adventures with the Binoculars last year, and found it a rather transfixing sight.

The greyness, incidentally, was due to the way our eyes have evolved: in the dark, most things look grey because the cones in our retina (which detect colour information) struggle with faint light. Unfortunately all my rods and cones had to work with was the small amount of light that had travelled 2.5 million light years and fallen into my 130mm-wide telescope, and at that distance things get spread pretty thinly.

Just as I was getting completely lost in my explorations of the cosmos, I heard a peculiar ‘splat’ sound next to me. Followed by another, and another. I turned the bike light on.

It was a frog.

I had to temporarily abandon my observations at that point, due to my irrational fear of frogs. I threw a couple fo small coins and pebbles at it to try and shoo it away, but in defiance it splatted its way over to my tripod, sat on my copy of the Sky At Night magazine for a bit, looked at me, waited for a while, and eventually disappeared.

By that time the Andromeda Galaxy had moved on: this was to be my first test of my calibration, and luckily adjusting the Right Ascension control brought Andromeda’s Galaxy back to the centre of the view. Not bad, hey?

Looking forward to viewing the Pleiades later this winter, finding my first planet and generally getting into this.