Do you have an astronomer on your Christmas list? (Stock photo)

Star Gazing: Binoculars on the Christmas list

Advice on buying a gift for the astronomer on your list

The range of things available to backyard astronomers is now, er, astronomical. Choosing presents for the family astronomer is more complicated than ever. That means unless you also share that interest, getting anything for an experienced backyard astronomer should be done in response to hints, notes left around or other useful information about what he or she wants.

If necessary, insist that Santa wants a list. On the other hand, if your family astronomer is a beginner, then things are easier. If there are no binoculars in the house, then think of getting some for Christmas. These are great for looking at the moon, star clusters, exploring the Milky Way, and for searching for comets.

A pair of binoculars consists of two telescopes fastened together so they point in the same direction. Binoculars are described by two numbers, for example, 8×30. The first number is the magnification — how many times closer it makes something look. The second is the diameter of the objective lenses in millimetres. Magnification is nice, but the most important number here is the size of the objective lenses. Most astronomical objects are faint, so catching as much light as possible is important.

One can get huge binoculars that are wonderful astronomical instruments, but they are heavy and will need tripods to hold them steady. If binoculars are not easy to hold still while you look at something for a few minutes, they are too heavy. In addition, tiring hands start to shake, and magnification makes the shaking more of a problem. So we have to compromise observing power with convenience and usability. For small hands maybe 7×40 (seven times magnification with 40mm objective lenses). For average observers, 7×50 binoculars are good, general-purpose instruments to have around. One alternative which is expensive but getting cheaper is a pair of image-stabilized binoculars. These have sensors and a little computer inside which detects the shaking and wobbles little mirrors or prisms to correct it. These devices are amazing things to use. If the astronomer has any problems with holding things still, these binoculars will open doors to a new realm of enjoyment.

Binoculars are getting better and better, and the two potential problems described here are getting rarer and rarer. However, it is best to keep an eye open for them, especially when buying from anywhere other than a science store. The first is chromatic aberration. This arises because the lenses are not focussing all colours equally. Look at the edge of a dark thing against a bright one, like a roofline against the sky. The problem will show up as false colours. There shouldn’t be any. The second problem is the two telescopes making up the binoculars might not be pointing in exactly the same direction, a problem called poor collimation. This manifests itself as either a feeling of not-quite-rightness or you might even see double. Your brain can often correct this, but at the expense of discomfort and headaches. It should be possible to set up the binoculars so they are completely comfortable to use, for long periods.

If you have a science store or a good camera store nearby, go there. Try out the goods before buying. Another possibility is to talk to members of the local astronomy club. Otherwise, buy from a good dealer. I suggest buying an astronomy magazine, such as SkyNews (Canadian), Sky and Telescope (American) or Astronomy (American). The companies advertising in them are reputable and there are usually articles about hardware choices. Have a read before going shopping. I end with a warning though; you might get hooked yourself.

Mercury and Mars lie low in the southeast before dawn. Jupiter and Venus are close together very low in the southwest in the sunset glow, with Saturn a little higher and to the left. The moon will reach first quarter on Dec. 4.

Ken Tapping is an astronomer with the Dominion Radio Astrophysical Observatory near Penticton.

ken.tapping@nrc-cnrc.gc.ca

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