Telescopes and Lenses

24 02 2009

This is an exciting time in which to become an amateur astronomer. Never before have novice stargazers been presented with such a vast array of telescopes and accessories to pursue their hobby. Naturally, this brings the burden of choice. A bewildering variety of instruments make it difficult for the uninformed consumer to make the right decision. That’s what this entry is all about – to explain the options so you can choose the telescope that’s best for you.
Before examining the different types of telescopes available, it’s worthwhile illustrating some basic principles in order to understand how they work. The most important aspect of any telescope is its aperture, or the diameter of its main optical component, which can be a lens or a mirror – the fatter the tube, the larger the aperture. A scope’s aperture determines its light-gathering ability and its resolving power (the ability to see fine detail in an image).
What does this mean in real terms? With a 6-inch telescope, you can discern lunar craters that are as small as a mile across, which is half the size of those visible in a 3-inch scope under similar conditions. However, the same two instruments turned toward a faint galaxy on a moonless night would tell a different story. The 6-inch gathers four times the light of a 3-inch, not twice, so the galaxy would be four times brighter in the larger instrument. How is that? A 6-inch telescope has four times the light-collecting area of a 3-inch. Read the rest of this entry »


Comet Lulin

24 02 2009

A fairly bright comet is passing through the solar system right now: C/2007 N3 (Lulin), or just Comet Lulin to its friends. Over the next few days it’s passing very close to the position of Saturn in the sky, making it a very easy target to spot. Take a look at a map of Lulin’s position for tonight courtesy Jodrell Bank. Sky and Telescope also has PDF maps of the comet position for various dates.

Its position near Saturn in Leo means it’s up practically all night right now; it rises around sunset, so look East for it. With binoculars it should be pretty easy to find; its brightness is hovering just above naked-eye visibility, so it’ll be an obvious fuzzy ball near Saturn.

Spectacular Saturn Transit

19 02 2009

Something is about to happen on Saturn that’s so pretty, even Hubble will pause to take a look.

“On Feb. 24th, there’s going to be a quadruple transit of Saturn’s moons,” says Keith Noll of the Hubble Space Telescope Science Institute. “Titan, Mimas, Dione and Enceladus will pass directly in front of Saturn and we’ll see their silhouettes crossing Saturn’s cloudtops—all four at the same time.”

Hubble won’t be the only one looking. Amateur astronomers will be able to see it, too.

Transits like these are rare. “They only happen every 14 to 15 years when the orbits of Saturn’s moons are nearly edge-on to Earth,” says Noll. In 1995-96, the last time the geometry was right, Hubble photographed two (Titan and Tethys) and three (Mimas, Enceladus, Dione) moons transiting Saturn. This will be the first time the great telescope captures four.
The event begins on Tuesday morning, Feb. 24th at 10:54 UT when Titan’s circular shadow falls across Saturn’s cloudtops. About forty minutes later, the ruddy disk of Titan itself moves over the clouds.

“Titan is so big, you can see it just by looking through the eyepiece of a small telescope—no special camera is required,” says Go.

One by one, the smaller moons Mimas, Dione and Enceladus will follow Titan. At 14:24 UT, all four satellites and their shadows will simultaneously dot Saturn’s disk.

Titan transits Saturn on Feb. 8, 2009. (Christopher Go, the Philippines)
Titan transits Saturn on Feb. 8, 2009. (Christopher Go, the Philippines)

In Saturns Shadow

11 02 2009

After successfully observing Venus, the Moon and Saturn (with tiny Titan) last night, I thought it was apt to show you this impressive panorama of Saturn, taken by the Cassini probe, currently in orbit around the ringed planet. Read the rest of this entry »

Variable stars

10 02 2009

Looking up in the sky on any given night and you’ll see thousands of stars. Each star appears to be slightly different in brightness – some are stunningly bright, whilst others are just on the edge of visibility. However, there are stars that, if you are very observant, seem to appear and disappear over a period of days, weeks or even months or years. These are known as variable stars. Read the rest of this entry »