A great number of galaxies, star clusters and planetary nebulae are visibly within reach of urban stargazers. But a host of urban stargazers are at a major disadvantage when attempting to obverse them through telescopes, binoculars or the naked eye. There are a host of reasons for this. While the moon and the brighter planets show very little sign of interference from light pollution, a host of deep sky objects can barely be seen. Double and variable stars show relatively well, but it’s a fact that the fainter and more vague forms can be tough to see even under the most pristine conditions. They too succumb to the overpowering very brutal interference of city lights.
But this does not mean that your journey into the cosmic world is impossible. There are a host of sky objects which are visible even under the stress of less ideal conditions. The reason for this is that some objects have what is called ‘high surface brightness’. This is how a vast array of double and variable stars, find their way through the sky’s urban sprawl. Those who are relatively inexperienced at deep-sky observation, often attempt to judge if a specific object will be visible through their telescope or binoculars basing their decision on the object’s listed magnitude. This is not the way to judge sky object visibility at all. Yet it is one of the most common mistakes made by amateur stargazers.
Often times, amateur astronomers reason that if they can observe an 11th magnitude star through their telescopes, they will be able to see an 11th magnitude galaxy just as easily. When they aim their telescopes where the galaxy is said to be located, they see nothing at all. Yet the 11th magnitude star is very visible. They scratch their heads and wonder why. The problem here is in the manner in which tradition has expressed sky object brightness. The magnitude system which was created by the Greek astronomer Hipparchus, was initially designed to rate the brightness of stars and other light sources such as planets which were seen by the naked eye. When the telescope came into the equation, the system needed to be reassessed and expanded on. These days when astronomers speak of magnitude of a star cluster for instance, they are actually referring to the ‘integrated magnitude’.
Now if we can not use a deep-sky object magnitude to judge visibility through a telescope what do we do? Experienced astronomers use an object’s surface brightness. This means that they assess how bright an object appears across its area. So urban deep-sky observers should focus on high surface brightness objects when star gazing and leave the others until they can escape the urban areas. A vast array of globular star clusters, planetary nebulae and open star clusters are deemed high surface bright. These make them the ideal targets for peering through light pollution.If you are hoping to observe planetary nebulae, try using narrowband nebulae filters.
These suppress all wavelengths of light save select wavelengths where these specific objects emit most of their own visible energy. Many observers prefer to hold these between two fingers rather than screw the filter to an eyepiece. When going back and forth quickly, you will find that the planetary is much easier to find. This is because the filter dims stars more than the nebula. This is what many astronomers call the ‘in-out-technique’.Another technique many urban astronomers use is ‘averted vision’. If a faint object is hard to find, look to one side or the target. The targets weak light will often fall on a more sensitive area of the eye’s retina. If this fails to work, try to centre the object and tap the side of your telescope. Sometimes if the field is gently jiggled, marginal objects reveal themselves. Tap gently, just enough to give your telescope a soft shake.
One thing to note is that the higher an object sits in the sky, the better chance of viewing it in the night sky. Anything relatively close to the North Star will be a little more prominent and less likely to be affected by light pollution. You can see how this is true if you pan your telescope to see the hazy glow on the horizon. You will note a huge difference when you then aim your telescope high in the sky. Another thing to note is the light pollution is less prominent at night due to industrial lights being turned off, neighbours retiring for the night, less cars on the road and so forth. Choosing between 10pm and 3am in the morning to do your urban stargazing is highly recommended.
Think portability when choosing a telescope for enjoying urban stargazing. You may wish to head to high ground, an elevated look out etc. Toting a heavy telescope may be out of the question. Open field areas, parks, beaches, rivers, lakes and open golf courses will give you the best viewing sites. These have less light pollution to contend with. Fishing piers, football ovals will be great options as well. Now one may opt for a computerized telescope mount as these greatly enhance your chances of locating specific stars in the sky. But do remember the old adage “ You get what you paid for”, generic brand telescopes compromise the optics, electronics and so much more. Often giving you a blurry outline of sky objects and nothing more.
Add a tube extension, purchase eyecups which will block any stray light. Take along a red light torch to read your star chart. Dress comfortably and give your eyes ample time to adjust to the nightlight. And have fun, this is what stargazing is all about. The more you practice stargazing, the better your experiences will be.