Planetary nebulae

Urban Orion

The constellation of OrionOrion is not only the best known winter constellation, but it is also a great urban constellation. Thanks to its distinctive arrangement of rather bright stars, Orion shines through in heavily washed-out skies, even when few other constellations can recognized. It is also the home of the Great Orion Nebula (M42) big, bright, and easily visible even in washed-out skies. However, M42 is only the most famous of many interesting astronomical objects in Orion. And best of all for urban astronomers, quite a few of Orion's objects—like the constellation itself—can be enjoyed in light-polluted skies. Here is a run down...


Urban Messier Challenge

The Messier catalog lists some of the finest objects in the northern skies. Observing all of the Messier objects is one of the classic rites of passage for amateur astronomers. There are also a variety of challenges related to the Messier Catalog, the most famous of these being the Messier Marathon: a race to see all of the Messier objects in a single night. There are also binocular Messier challenges and photographic Messier challenges. My own addition to this is an Urban Messier Challenge: a list of Messier objects that are particularly challenging for urban and suburban observers dealing with skies washed-out by light pollution. In dark skies you can see all of the Messier objects with a 3 inch (75mm) aperture, but with heavily light-polluted skies you’ll have a hard time seeing the Messier objects on my urban challenge list even with significantly larger apertures. Here is the challenge list...


Herschel's Quandry

NGC 1514 (photo by Chris Cole)In Taurus just over the border from Perseus is NGC 1514, a planetary nebula with an important role in history. William Herschel, based on his experience resolving globular clusters, believed that all nebulae were clusters of stars that were too faint or too remote to resolve. But when he discovered NGC 1514 in 1790, Herschel encountered a solitary star “surrounded with a faintly luminous atmosphere”. This object forced him to revise his thinking and conclude that “Our judgement I may venture to say, will be, that the nebulosity about the star is not of a starry nature”.

Although officially listed at magnitude 9.4, NGC 1514’s relatively low surface brightness and its bright central star make it a rather challenging object to see from an urban environment. Even though it isn’t the most beautiful planetary, it is worth tracking down simply because of historical interest. Here is some information to help you find NGC 1514...

(Photo courtesy of Chris Cole)


Interesting Planetaries

The Eskimo Nebula, NGC 2392 Planetary nebulas generally make great targets for washed-out astronomers. Most of them standout well even in light polluted skies because they are usually rather small and therefore have relatively high surface brightness. Their small size also means they are best seen using relatively high magnification which helps to darken the background and boost contrast. Finally, planetary nebulas respond very well to narrowband filters, even when observing in urban environments. (Image: Glenn Hitchcock and Bob Cowart/Adam Block/AURA/NOAO/NSF)

Famous planetaries like the Dumbbell Nebula (M27) and the Ring Nebula (M57) are well known to most amateur astronomers and are spectacular objects even in light-polluted skies. But regardless of season there are always planetary nebulas well positioned in the sky for urban observers. Here is a list of good planetaries for washed-out astronomers…


UltraBlock and Small Scopes

Orion UltraBlock filter, 1.25 inchIf you peruse posts on Cloudy Nights and other forums on the web, you’ll find claims that narrowband filters don’t work well with small scopes, that you need at least 8 inches (or 10 inches, or 12 inches…) of aperture to get any benefit from them. I’ve never agreed, having used the UltraBlock to advantage with my 4.25 inch (108mm) Newtonian to see through local light pollution.

4.25 inch (108mm) Newtonian reflectionRecently, I put this hypothesis to the test with my 4.25 inch (108mm) Newtonian on a night with particularly bad haze and light pollution. It was a night on which 3rd magnitude stars were hard to see. I found that planetary nebulas which were invisible in the 4.25 inch showed up relatively clearly using the UltraBlock. So as far as I can tell, you can use the UltraBlock filter to help you see through light pollution just as effectively with small apertures as with large. Here are the details….


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