From city lights to deep space

In this second part of a series that looks at urban stargazing through four seasons, Rod Mollise reveals the wonders you can discover in the summer night sky...

- Rod Mollise

When it comes to deep-sky objects, in the summer the galaxies lying outside the plane of the Milky Way are setting and the marvels within our own Milky Way are on the rise. Urban observers don't have as easy a time viewing the deep sky in summer, as the air tends to be humid and moisture scatters light pollution, making the sky brighter. Nevertheless, it is possible to see a multitude of distant and beautiful objects; you'll just need to tailor what you are looking for according to the weather conditions. On humid summer nights look for bright star clusters, saving more difficult objects like galaxies for times when the weather is dry and the sky is dark.

Whatever the conditions, when deep sky observing there's one characteristic that's most important in the telescope you use - aperture, the size of its light-collecting lens or mirror. A telescope with an aperture of at least 200mm is recommended in areas with light pollution. However, one with a 250mm aperture will be as portable and only a bit more expensive - the extra 50mm shows many more objects and gives more detail, even in bright urban skies.

There are a few different telescope designs to choose from:

Newtonian reflectors, which use a large mirror to collect light, are the least expensive when it comes to cost-to-aperture ratio. But, as the tube in a Newtonian is open to the elements, expect to clean its delicate mirrors regularly. Medium to long focal length Newtonian reflectors are not very portable in apertures above 250mm, and Newtonian mirrors need to be aligned to each other (collimated) frequently.