I’ve been having a problem over the past few months of the focus in my scope drifting unacceptably out of focus when imaging targets around the sky. Even when staying on same target for extended periods of time there was a noticeable shift. In some extreme cases the collimation also appears to be way off. This seemed to be a rather severe case of mirror shifting that larger SCT’s suffer from. The solution to which is to securely fix the primary mirror within the cell, usually by threading bolts into the mirror from the back of the scope. This seemed to fit the symptoms I was seeing, though some people did mention that I shouldn’t bee seeing this sever an effect with a relatively small scope. So yesterday I decided to disassemble the scope and see what the back of the primary was like and if it would be possible to secure it. It didn’t take me long to discover a more likely cause. More »

One of the people at our table at the COSMOS star party this brought up the topic of long distance radio communications and the use of geostationary satellites to facilitate such communication. The idea of trying to image some of these satellites then came up and we discussed the possibility.

So last night I decided to give it a go. More »


My main interest st the moment is in minor planet astrometry, particularly of brighter Near Earth Asteroids. In order to get precise astrometry of these objects it helps if they are not moving in a single frame. Slow NEO’s can have rates of several arcseconds per minute so being able to take short exposures and stacking them is often required to get precise enough astrometry. It is possible to compute the minimum exposure needed for an asteroid by ensuring it’s movement does not exceed the FWHM of stars in your image, e.g. if an NEO is travelling at 4”/minute and you have a FWHM of 4” then an image one minute in duration will not show trailing. However it is also necessary to understand what the minimum exposure you can take with your setup is to minimise noise and maximise the signal to noise ratio. And it was necessary to understand the camera characteristics in order to make that determination. More »

m82sn Supernova in M82 from Earlier in the week, now designated SN 2014J. Quite a bright supernova. It’s bright because it’s practically next door – 12 million light years. This is a Type Ia supernvoa caused by a white dwarf in a binary system gaining enough mass to trigger new nuclear fusion and cause the supernova explosion.

Astrometrica is a great piece of software to analyse images to search for and record the positions of objects. However getting it to work with a DSLR image can be a bit tricky. Here’s how I do it: More »

Before I built the observatory I used to only use the laptop when I was going to try imaging. Now the laptop is almost always used unless I really am only doing visual astronomy and don’t want to bother with planetarium software, in which case the laptop and camera are a distraction to trying to glimpse the universe through Dublin’s light pollution. Here’s how I have things set up. This may not be ideal for you.

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Some friends after seeing a strangely cut bit of cardboard in the observatory suggested I write a blog post about it. Those of you who do astrophotography won’t need an introduction to the Bahtinov Mask, but this post might be of interest to the rest.

Getting focus right in astrophotography isn’t easy. Autofocus doesn’t work like it does for normal lenses. And judging it manually is error pone, you can estimate when a star looks like a point, but there is a large margin of error in that estimate, a bright star may look like a sharp point but the fainter stars may still will be blurry. This is especially true in poor seeing where star image blobs can look the same over a large focus range. More »

This morning I got this one line email from the International Astronomical Union Minor Planet Center:

Your site is now code Z72.

So Cademuir observatory is now officially recognised by the MPC! In order to obtain an observatory code it’s necessary to observe some minor planets (in the 1000-400,000 range) of varying magnitudes, at least a couple of times a night over at least a couple of nights and record their positions to an accuracy of within 1″. Using the (.25 scope with a focal reducer and a DSLR I was able to get most reading accurate to < 0.5″. I’ll post a full writeup of the process in future, for now I’m going to celebrate and hope for clear skies to see ISON in the morning!

I’ve already posted this on facebook, so apologies to friends who’ve already seen it! Jupiter taken 12th January 2013, 22:17 : More »

The latest improvement in the observatory is lighting. I needed something that was low power, needed to be red, needed to be white, preferably dimmable, preferably remote control. There didn’t seem to be anything in the local shops, but I found an LED solution on ebay costing a whole $18.90. At that price I’d have to give it a go! More »