June 6, 2008

In Today's One Minute Astronomer...

Urban Stargazing

Spending your vacation in the city this summer under hazy light-polluted sky? Here’s how to make the best of it.

The Basics

• City lights brighten the background sky, making it hard to distinguish extended nebulae and galaxies that have low surface brightness. If the sky is brighter than what you're looking at, the biggest telescope in the world won't help you see any better.

• The solution? Use the laws of physics in your favor. Stick to objects that are brighter-much brighter-than the washed out city sky.

• The ultimate in brightness, of course, is the sun. With a good white-light solar filter, you can track sunspots, faculae, and granulation. If you can afford a scope with a hydrogen-alpha filter, you'll see the fiery orange photosphere and immense prominences flying off the edge of the solar disk. An incredible sight.

• Many think the moon isn't worthy of observation. But explore the moon's terminator at high magnification, and you'll feel like an Apollo astronaut. And shouldn't we all learn, as a matter of pride, the places where men first walked on the moon?

A Deeper Look

• In clear steady sky, any of the planets look as just as good from the city as from a dark-sky sight. If you look closely, they are endlessly fascinating. At least one of Mars, Jupiter, or Saturn is nearly always visible. And have you seen Uranus or Neptune lately?

• Star clusters, whether ancient globular or nascent open clusters, make a fine sight from the city. The best of summer: M13 in Hercules (a globular), M11 in Scutum (open), M22 in Sagittarius (globular), and the Jewel Box in Scorpius (open… great in binoculars).

• The countless double stars in the summer sky offer a city dweller endless pleasure. Savor the contrast in colors, brightness, and separation. Try Albireo in Cygnus, epsilon Lyrae, alpha Hercules, and 70 Ophiucus, a short period double star you can actually watch revolve during your lifetime.

Good To Know

Thinking about buying a “light-pollution” filter for your telescope? They won't improve the view for stellar objects like galaxies and star clusters. But a good OIII or UHC filter is a great help for planetary nebulae like M57 and gaseous nebulae like M17 in Sagittarius.

Personal View

Enjoy what you have, even if it’s the fish-grey skies in the heart of a big city. There’s endless enjoyment if you know what to look for.

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