Galaxies

16 03 2009

On a typical night, looking into the sky, you can see somewhere between 500 and 6000 stars, depending on how dark your night sky is. If you live in a reasonably dark area, you may be lucky enough to see a faint, diffuse band stretching across the sky, from horizon to horizon. This band, known as the Milky Way, is the plane of our home galaxy.

It was Galileo who discovered that this band consisted of an almost uncountable number of stars, after he turned his telescope to the sky. Prior to this, it was believed that the Milky Way was a ‘cloud’ that spanned the entire sky.

360-degree photographic panorama of the Milky Way. (Digital Sky LLC)

360-degree photographic panorama of the Milky Way. (Digital Sky LLC)

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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.





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 »





Clusters

20 01 2009

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. Read the rest of this entry »





Nebulae

13 01 2009

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). Read the rest of this entry »





Impressive Leonid Meteor?

27 11 2008

Whilst talking about meteors and discussing both the size, frequency and origins of meteor showers, I usually mention the phenomena of fireballs (or bolides). These are larger than average specks of dust or debris that can cause an impressive meteor that in some cases can even leave a ‘tail’ like a comet and light up the sky for miles around.

During the annual Leonid meteor shower, it appears that there may have been one such bolide in Canada… Read the rest of this entry »