This is the question just about all new telescope owners ask after viewing the moon and maybe the bright planets. What else is visible in the sky, and how can I find them? The objects visible in the sky can be divided into two types; Planetary objects, bodies belonging to the solar system and deep Sky objects, bodies that lie beyond the solar system.
Planetary objects include the planets themselves, the moon and sun, plus satellites of the planets, asteroids and comets. The one thing planetary objects have in common are that they move. Therefore they cannot be found on star charts other than those that are specific for a point in time, like those found in the Stellar Sentinel. Some books on observing also give the constellations that bright planets reside in for a few years for a few years.. The best place to find planet location information is the planet sections of Astronomy and Sky and Telescope magazines, which can be found locally in book stores. Members may also subscribe to Sky and Telescope at a discount through the society.
Of the planets visible to the unaided eye, Mercury is hardest to find because it lies so close to the sun. The best times to spot it are in autumn mornings near and a week after greatest western elongation, its greatest apparent distance from the sun, and in the spring evening twilight from a week before to greatest eastern elongation. A telescope will show a very tiny half illuminated disk.
Uranus and Neptune require a finder scope to even spot as faint starlike points. In the telescope these become noticeably larger than stars. Uranus has a blue hue, while Neptune is decidedly greenish. Spotting Pluto, however is out of the question unless your telescope has a diameter of 12 inches of wider.
Planets are the objects that can benefit from using high power. However telescopes do have a maximum usable magnifying power. It is 60 times the diameter of the objective in inches. So a 60 mm objective, that's 2.4 inches, can supposedly show added detail up to about 144 power. Any more power gives a fuzzier, dimmer image, despite what the telescope manufacturer might tell you. It's a law of nature, like the impossibility of exceeding the speed of light.
Spotting asteroids is like spotting Uranus or Neptune, except asteroids always look starlike, thats what the word asteroid means. Charts for finding the brightest of these, like Ceres and Vesta can be found in the before mentioned magazines a few months before their closest approach to the earth. You may have to sketch the suspected asteroid in its star field, and check to see it it moved a few nights later to make sure you've bagged it.
When lead time permits, comet finding charts can also be found in the magazines. However for newly discovered comets, an ephemeris or list of positions may be your only guide. Flashy comets like Hyakutake and Hale-Bopp are the exception, but there are up to a couple dozen discovered or recovered each year. The overwhelming number of comets are only visible in telescopes.
As you've probably noticed, even when you're looking for solar system objects, a knowledge of the stars and constellations is essential in finding them. If you've skipped the study of the constellations, and got a telescope to see the 'good stuff', now's the time to sit down and learn the constellations, so you can find them.
One good book for the brighter constellations is the little Golden Book Stars, my first constellation book. I recently bought the book for my grandson, as I had his mother, years ago, and as I had bought mine back when the universe was only half the size it is today.
After learning some of the constellations, the next thing to do is get a good set of star charts, so you can star-hop to your favorite object. About the most inexpensive charts are within the book called A Field Guide to the Stars and Planets published by Houghton Mifflin. The scale of the maps is small but they show dim stars that can be seen in finder telescopes. Remember that finder telescopes generally give an inverted image, so you may have to turn the star chart upside down to make sense of the star patterns.
Star charts really come in handy for locating deep sky objects (DSOs). The good news here is that DSOs stay put, so their locations are included on the charts. So what kind of deep sky objects are there? Their are double stars, star clusters, nebulae and galaxies.
Double or multiple stars are stars that appear near to each other. They may be true binary stars that orbit one another, or just accidentally in the same direction from earth. There are Mizar in the Big Dipper, Alberio in Cygnus the swan, Gamma Leonis, and Beta Monocerotis, to name only a few. OK. you'll also be learning some Latin and Arabic names and Greek letters.
There are two kinds of star clusters. The first type is the open or galactic star clusters, generally hanging around the Milky Way band. Most of these are easily resolved into individual stars with a small telescope. Harder nuts to crack are globular star clusters, huge star groups of hundreds of thousands of stars. None are very close, and the easiest of them requires a telescope 6 inches in diameter to resolve.
Nebulae, plural of nebula which is Latin for haze come in a variety of types. Planetary and emission nebulae are the types best seen with small telescopes. Planetaries are so named because some look like the planets Uranus or Neptune. These are small puffs of gas dying stars let out as they shrink. Emission nebulae signal the birth of stars and are large.
Galaxies, which were misnamed nebulae before their true nature was discovered are found away from the Milky Way because they are Milky Ways in their own right. Photographs of some of these show a spiral structure, but this is usually lost to the eye at the telescope.
There is a wonderful list or catalog of many of the brightest of these DSOs. It was compiled by a comet hunter 200 years ago, who found these objects a nuisance. Today Charles Messier is more famous for his list than the 12 comets he discovered. Highlights of the Messier Catalog will be presented next month.
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