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Astronomy

Naief Khatri

Naief Khatri

Astronomy is the study of stars and the heavens. It has been in the news quite a bit lately, with the annual Perseid Meteor Shower in August 1998 and  the Hale-Bopp comet in April 1997. Astronomy is also a relatively inexpensive hobby to pick up simply go to your local library scan astronomy books and recent magazines and start studying those evening skies.

The first and foremost thing, before cultivating this hobby, is to buy or borrow a good telescope. Telescopes help in gathering light, make dimmer objects brighter and visible to naked eye. They magnify and thus make small objects visible.

Once you have got the telescope, you need to know how to use it and to make optimum use of it . Hence we have given a few guidelines that are intended for a beginner with a small telescope, who wants to know the night sky and recognize a few of the brighter objects.

A few basic things need to know:

  • The magnification of your telescope depends on the eyepiece you use. The shorter the focal length, the higher the magnification. The focal length is mostly printed on the eyepiece. It is a number between 5(mm) and 30(mm). A low number denotes a short focal length. Some telescope sets come with a Barlow, which has the effect of multiplying the magnification. For your first experiments don’t use the Barlow.
  • When you go outside, your eyes will adapt to darkness. Once they are (after about half an hour) don’t look at bright lights. If you are using a star chart, use a very dim light to look at it. (Some people like a dim red light)
  • Your telescope , when taken from a warm place to a cool night  takes a little time to adjust to the outside temperature. Put it outside for about an hour before you start observing.
  • Look for a really dark observing site. t’s worth it. Though you may start in your backyard, later on you will need a really dark place. As a rough guideline, you need to be able to see at least “hundreds of stars” for your first try.
  • Take care that you keep yourself warm. When you get cold, the fun is over.
  • Last but not least, plan your observing session and try to stick to the plan. There is nothing more disheartening than standing outside (in the cold) and not knowing what to try next. It is also very interesting to keep a logbook of what you did, how you did it, and what the result was.

The preparation:

You will probably need some warm clothes, a localized star chart, a dim light to illuminate the star chart with, a binocular (just borrow one for the occasion) and a list of objects you want to look at.Localized star charts may be found in papers or in magazines. There are some on the web as well. Another option is to buy an astronomical yearbook. It has the maps, and will describe what objects are bestfor a given month.

You will need to check (and correct if needed) that the finder and themain telescope are properly aligned. You can do this during the daytime by pointing the telescope at an object that is far away. When the telescope is pointed at that far away object, look through the finder and check if it is pointed at the same point. Compare the center point of the view. If it doesn’t  agree, then adjustthe position of the finder until it does.

If you have a reflector and you feel up to it, you can also check the collimation of your telescope. But if you bought a ready made telescope you can also skip this for the first couple of sessions, until you feel more familiar with it. Instructions on how to collimate are written in the manual of your telescope.

The observation list, and a suggestion for the first time:

Now prepare a list of what you want to do:

  • Find stars on the map in the sky, and identify the constellations “Ursa Major” and “Orion”.
  • Find the north pole star,and identify the constellation “Ursa Minor”.
  • Find Jupiter.
  • Look at Jupiter with the binoculars.
  • Insert the eyepiece with the longest focal length.
  • Aim the scope at Jupiter using the finder.
  • Look through the scope enjoy the view.
  • Look through the scope again, compare the view with what you see through the finder and try to guess at the relative sizes of the sky you see in both.
  • Compare the view through the telescope and the binocular, again look for the relative sizes of the sky you see in both.
  • Now insert the next eyepiece, the one with a focal length just below the first and repeat the above points.
  • Do the same for all eye pieces, note the effect of each eyepiece with respectto size of the image, sharpness and brightness. You will probably notice that at the highest magnification the view becomes “blurry”and you don’t really see many details.
  • If you have one, insert the Barlow in the longest focal length eyepiece and repeat.
  • Repeat step 5 to 13 for an other objects, like the Saturn or Mars.
  • After an hour or so, stop for the night and go back inside. Try to recapitulate what you have done, and write it down in your log book. Try to make a few sketches of what you have seen.

Some other tips:

Donot look at the sun, NEVER !.

The upper practical limit on magnification is about 2 times the aperture in mm, or 50 times the aperture in inches. (Aperture = diameter of your main mirror, or main lens) A lot of telescopes are sold with unusable magnification claims. In fact, with less than excellent optics you won’t even get close to the above mentioned magnification limits. Once you get to the limit for your telescope, you will notice that it is no longer possible to get a sharp image.

You can calculate the magnification by dividing the focal length of the telescope by the focal length of the eyepiece. When you use a Barlow you have to multiply the number you found by the power of the Barlow.

The amount of detail you see, depend on the contrast. This is why darker sites offer better viewing. If the background illumination can be decreased by one or two magnitudes you will see a much better image.

Some specifications for beginner scopes:

  • Planetary scope: 15 cm (6″) f/10
  • General purpose: 20 cm (8″) f/8
  • Deep sky: 25 cm (10″) f/6
  • For all scopes: Dobsonian mount, full thickness mirror, mirror glued to a three point cell. The radius of the fully illuminated field 5-10 mm (1/5 – 2/5 “)

Conclusion:

So now you have gathered enough information for your first night out. So get started right away.
Happy Viewing.

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