From City Lights to Deep Space

In the first part of a series that looks at urban stargazing through the four seasons, Rod Mollise reveals the wonders you can discover in spring

- By Rod Mollise. Photographs by Robert MooreIstock, Getty Images, M-Gucci, Chris Rogers, Bernhard Hubl, Christoph Kaltseis, ccdguide.com, Johannes Schedler, Pete Lawrence

Urban astronomy is not for the fainthearted, but persevere and you will find a wealth of celestial treasures that await discovery, even under bright night skies.

Many deep-sky objects are visible even in brightly lit urban areas. Take open clusters, nests of thousands of newborn suns, deep-sky objects which are the least harmed by light pollution. More tightly packed globular clusters are very old and light pollution takes its toll on them. While many are visible in the city with smaller aperture telescopes, most are just round smudges with no individual visible stars.

Galaxies can be challenging for urban observers to see. This doesn't mean you can't see them, you just won't see much detail. But diffuse nebulae are the objects most harmed by light pollution; even with a high-quality light-pollution reduction (LPR) filter screwed onto the eyepiece, dimmer emission nebulae can be a challenge to see. Planetary nebulae are not as harmed by light pollution. If they are tricky it's because they are difficult to distinguish from stars.

Key Kit

The most important characteristic of a telescope used for deep-sky observing from any site is aperture - the size of its light-collecting lens or mirror (the 'objective'). The superior light-gathering power of a larger telescope is even more important in the city. From a light-polluted area, you'll need one with a light-collecting lens or mirror with a diameter of at least 200mm. Inexpensive Dobsonian reflecting telescopes are a good balance between price, performance and portability. However, a 250mm Dobsonian is almost as affordable and portable, and the extra aperture makes a difference.