Comet Lulin

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

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)

In Saturns Shadow

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.

Variable stars

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.

Eclipses

An eclipse (from the Greek ekleipô, “to vanish”) is an astronomical event that occurs when one celestial object moves into the shadow of another. The term is most often used to describe either a solar eclipse, when the Moon’s shadow crosses Earth’s surface, or a lunar eclipse, when the Moon moves into the shadow of Earth. However, it can also refer to such events beyond the Earth-Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its parent planet, or a moon passing into the shadow of another moon. An eclipse is a type of syzygy (a line up of astronomical bodies), as are transits and occultations. Eclipses are impossible on Mercury and Venus, which have no moons.

Clusters

Star clusters are groups of stars that are gravitationally bound. Two distinct types of star cluster can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group.

Nebulae

The term “Nebula” (plural nebulae) has a varied use in the history of astronomy. In pre-telescopic times it was used to distinguish fuzzy objects that looked different to the point like stars. Most nebulae known at that time have been shown to be open star clusters. The term nebula was a catch-all term used for what we now call deep sky objects. If you have an old astronomy book, the Andromeda Galaxy was once called the Andromeda Nebula.

In early telescopic times, the nature of these objects was still widely unknown. With open clusters resolved, still all other deep sky objects were summarised as “Nebulae”. Only the use of large telescopes, the discovery of spectroscopy and the invention of photography in the second half of the 19th century made it possible to distinguish “real” nebulae – i.e., gas and dust clouds – with certainty from objects made up of stars (globular clusters and galaxies).