click above to sign up

Dalriada n:
Kingdom of the Scots,
home of the residents

Mercury in transit

It’s not often that an astronomical event coincides with perfect viewing conditions in Glasgow. And it’s quite unusual that I can observe a must-see astronomical event while having lunch in our conservatory. So I was quite looking forward to the transit of Mercury on 9th May.

Mercury is the smallest planet in the Solar System and the one closest to the Sun, with an orbital period of about 88 Earth days, which is much faster than any other planet in the Solar System.

A transit is when a small astronomical body passes in front of a larger one, unlike an eclipse when the front body is large enough to completely occlude the one behind it. Transits of the Sun by Mercury from our point of view can occur, in May or November – May ones are best because Mercury appears a bit bigger then, and it’s very small relative to the Sun even then. The next May transit is 7th May 2049.

I set up my kit in the garden…:


mount and camera are both powered via a mains extension, batteries might not last long enough


Usually it’s a 200mm aperture, now reduced to 60mm + solar safety film.

… and in the conservatory:


With applications on the laptop I can control the telescope mount and the camera:
eqmod EOS500Dremoteliveview zoomview
After that things went fairly well, except for an unforeseen problem with ‘meridian flip’, when the mount tried to tie itself in a knot after the sun crossed the meridian (the line straight overhead between due North and due South). The counterweight arm crashed into a tripod leg and the motors could drive it no further – fortunately no serious damage was done and I managed to sort it out by rotating the scope by 180° round both its axes. This is a known problem when tracking celestial targets which cross the meridian but normally the Sky Watcher Synscan controller is smart enough to avoid it. But unfortunately it is also so smart that it refuses to cooperate with anyone trying to point its telescope at the Sun, which could be a very dangerous proposition (unless the scope’s normal 200mm aperture, is reduced to 60mm and protected further by solar safety film).
Finally, here is Sky at Night Magazine’s trailer:


and here is my composite result (from 13 overlaid images, with time off for meridian flip problems!)