There's a special treat waiting for you this Halloween.
Remember how, in the "Peanuts" cartoon, Linus would wait every Halloween for the Great Pumpkin to appear in his pumpkin patch? Well, this Halloween there is a nice big orange pumpkin of sorts right in the middle of the Beehive star cluster in Cancer.
To receive this treat, all you have to do is stay up past midnight on Halloween into the wee hours of Sunday, and look for the planet Mars, now becoming quite bright at magnitude 0.4.
If you haven't looked at Mars lately, you'll be surprised at how bright it's grown. It now equals the bright star Betelgeuse in brightness, shines significantly brighter than nearby Castor, Pollux, and Regulus, and is exceeded only by Sirius (the brightest star in the sky), Capella, Rigel and Procyon.
Mars typically appears orange or ruddy compared to other planets and the stars. In a small telescope, it becomes a fuzzy orb rather than just a point of light.
Zeroing in on Mars with binoculars or a telescope will show that it is embedded in the beautiful open star cluster, number 44 in Messier's catalog, known as the Beehive. At 590 light-years distance, it is one of the closest star clusters to the sun. It's also unusual in that it shines brighter than any of the individual stars in the its constellation, Cancer.
The Beehive seems an appropriate name, since the cluster resembles a swarm of glowing bees. Its alternate name, Praesepe, is a bit more puzzling. It is Latin for "manger" and relates to an alternate version of the constellation Cancer, where two nearby stars, Asellus Borealis and Asellus Australis, are named for donkeys, gathered around the central manger.
If you observe Mars with a telescope, take careful note of its exact position against the background stars of the Beehive, perhaps making a simple sketch. An hour or so later, check the position again, and you will see that it has moved slightly. There's even a chance that from your particular location Mars, in its orbit around the sun, will actually pass in front of one of the Beehive's stars, causing an occultation.
Besides growing brighter, Mars is also increasing in size as it moves towards opposition, the point opposite the sun in the earth's sky, on 2010 Jan. 29.
At present Starry Night shows it to have a diameter of 7.9 arcseconds at a distance of 1.182 astronomical units. 7.9 arcseconds is only 0.4 percent of the moon's diameter, equivalent in size to a tiny crater on the moon. An astronomical unit is the average distance from the Earth to the Sun: 93 million miles, making Mars 110 million miles from Earth. By Jan. 29 it will have almost doubled its size to a diameter of 14 arcseconds at a distance of 0.664 astronomical units, a mere 62 million miles away.
The coming opposition of Mars is known as an aphelic opposition, since it occurs close to Mars' aphelion (its greatest distance from the sun). Compare its size with what it was in August 2003, a very favorable perihelic opposition: 25 arcseconds and only 0.373 astronomical units away.