Mar 31 2012

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How to Become a Planet Hunter

As the planets put on a show, astronomer Mark Thompson discusses how you can hunt them down.

By Mark Thompson
Fri Mar 30, 2012 12:26 PM ET


This is a great time to observe Venus, Jupiter, Mars and Saturn.
You can use a powerful telescope, but even a pair of binoculars at 20x magnification will do the job.
Use a planisphere or a planetarium app on your smartphone to quickly locate the planets.
Venus (top), and Jupiter (bottom center) appear in the night sky near a crescent moon on March 25, 2012 over London. – Ian Gavan/Getty Images

This last month saw a boom in planetary sightings across the world. Wherever you observed the night sky from you couldn’t fail to have seen, and been impressed by, the view of Venus and Jupiter dancing around in the twilight after the sun had set.

While these two planets were setting, Mars and Saturn were rising in the East, continuing the celestial show. It’s easy enough to still spot these planets with the naked eye, but to really get the most out of them a telescope or powerful binoculars are needed.

There is no better time than now to learn about how to get the most out of your equipment for planet spotting.

ANALYSIS: Impressive Astronomy Photos Using a… Webcam?

First things first: magnification. To be able to see any decent level of detail, a magnification of at least 20 is needed. Anything less than this and you’ll just see the planets as bright stars.

Telescopes can easily handle this magnification, but if you are using hand-held binoculars you might want to think about getting a tripod to mount them on. Not only will the binoculars magnify the object under study by 20 times, but any tiny movement caused by hand shake will also be magnified leading to a very wobbly and unpleasant view.

Binoculars usually have a fixed magnification, which is described by a set of numbers — for example, “7×50” means “7 times magnification” and “a lens diameter of 50 millimeters.”

To work out the magnification of a telescope, you divide the focal length of telescope by the focal length of the eyepiece — for example 1000 millimeters (telescope) divided by 15 millimeters (eyepiece) would give a magnification of 67 times.

If you are using a telescope, and magnifying the planets much more than a set of binoculars are capable of, you may still find that you get a very disappointing view. This is caused by a few factors.

The most common cause of poor-detailed images is atmospheric conditions. If the atmosphere is very turbulent (i.e. the ‘seeing’ is poor) then the incoming light from the planet will get bounced around as it passes through the atmosphere, leading to a ‘bubbly’ or rapidly changing image.
star twinkle

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You may get moments of good seeing but you’ll require some patience. There is nothing you can do about poor atmospheric seeing and you can tell if this is the case as the stars are ‘twinkling’ more than usual.

Another cause of poor image quality may be the result of not letting your telescope cool down. Telescopes can take quite some time to cool (sometimes hours) so it’s worth setting up your telescope outside before nightfall to let it cool — but be careful about dew forming on the optics!

Another cause of poor image quality is collimation, particularly in reflecting telescopes that use mirrors. Make sure the optics are all aligned properly and you can be sure you are getting the best out of your telescope.

Now that you have a nice sharp image of your favorite planet you might like to try enhancing the view you can see through the use of color filters:

Venus is generally quite bland and seemingly featureless but a deep blue filter can enhance subtle detail in its thick atmosphere.
Mars has lots of detail accessible to the amateur astronomer, but more can be seen. Try an orange/red filter to increase the contrast between dark and light areas like the popular Syrtis Major region or perhaps a green/blue filter to enhance the polar ice caps.
Jupiter is a great target and detail in the bright areas of the gas giant’s belts can be enhanced with a light blue filter and the darker belts like the northern and southern equatorial belts can be enhanced by a green or blue filter.
Saturn’s stunning ring system can be enhanced by a light green filter, which will also pull out detail in the belts of the planet’s atmosphere.

ANALYSIS: High-Octane Social Astronomy

Of course, perhaps the trickiest thing of all is to find the planets in the sky in the first place, but help is at hand. You can either use a planisphere to locate them or, if you own a smartphone or tablet computer, you can load applications that will detect where you are on Earth and where you are looking to show a graphical representation of the sky and what’s in it, including the planets.

However you go about finding the locations of the planets, you’ll be amazed at what you can see.

The first planet I found was Saturn and seeing it for myself, live, was mind blowing. It wasn’t a picture in a book, nor an image from some far-off space probe, but a live view of an alien world… It was incredible and I recommend, no, I insist that you give it a try for yourself. You won’t be disappointed.

There are some useful tips on my website (MarkThompsonAstronomy.com), including more information on planetarium software for finding planets.

Tags: Apps, Astronomy, Night, Optics, Telescopes

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