In an ideal world, we'd all have our telescope observatories at the top of mountains with totally uninterrupted views in any directions. For those of us who do not have a handy mountain in the back garden, we have to contend with trees and houses getting in the way. This creates a hard limit on the objects we can use for Astrophotography. It would be nice to have a perfect horizon, but most of us cope by patiently waiting for the required target to arrive in a region of clear sky. British astronomers have lots of patience!

Most of us modern astronomers use computerised star chart programs. Such software allows you to enter the horizon limits in each direction and create a local horizon line (yellow on the chart) above the zero degree horizon (grey on the chart).

With the installation of my new homemade telescope mount combined with the passage of time, my map of the local sky has changed. The annoying huge tree to the south east has grown, whilst pruning has created some gaps in other areas. As it was cloudy today, I decided to recreate my horizon map.

This is a simple yet time-consuming task. You have to slowly move the telescope around the sky, using the scope to locate the line between the sky and the trees/houses. The telescope mount tells us at which altitude the telescope is pointing. This information is recorded around various points of the sky - the job only takes a hour or two.

Then is is a case of entering this data into your planetarium software (Skymap wins an award here for dreadful such a dreadful interface) and use the resulting plot when planning your observations. When it is dark, it is very easy to suddenly find yourself shooting images through a tree and wondering why the stars like so odd. With a decent chart setup it is easy to avoid silly mistakes.

Here we can see my plots in each direction. As it happens, most of my astrophotography is done in the north east, as this does the darkest sky. Many interesting objects appear in the south as well, but I can usually only track these for a couple of hours, so it is harder to get a decent image.