For the week including August 6, 2010

Mercury Venus Saturn Mars Larger Illustration

GATHERING OF PLANETS IN LEO

The month of August begins with a very rare astronomical event – a wonderful grouping of four planets in the constellation of Leo, the Lion. This gathering of Mercury, Venus, Mars and Saturn will continue for about week before officially Mars crosses into the adjacent constellation of Virgo, so you’ll have plenty of nights to enjoy the show. It might be a good idea to take advantage of this opportunity – it will be many years before we have another conjunction of planets as nice as this.

After the Sun goes down, and the sky begins to darken, look to the western horizon and you will see the planets clustered in the constellation of Leo, the Lion. The Lion is easy to pick out because it’s home to one of the most distinctive sets of stars in the sky. The head and heart of the Lion form a prominent shape that most folks describe as a reversed question mark, or a starry sickle. The planets themselves will look wonderful in modest backyard telescopes, but even a set of binoculars will capture some of their marvelous attributes.

Mercury: Usually, heavily cratered Mercury is one of the toughest planets to find. Since it’s tiny in size and is the closest planet to the Sun, it’s easy to lose it in the glow of sunrise or sunset. Mercury’s rapid orbit moves it among the stars very quickly, so watch for this small “star” as it climbs toward its rendezvous with Regulus, the star that forms the dot of Leo’s question mark, toward the end of next week.

Venus: Venus is the brightest of the planets and with an orbital period of 225 days, like Mercury, it moves fairly rapidly among the stars. Venus will have climbed high enough in the sky to sit right next to Regulus by August 5th and 6th. Because Venus is closer to the Sun, its smaller orbit lets us see it only near dusk or dawn, but this feature also allows folks with telescopes to see the planet go through crescent phases like the Moon.

Mars: Mars has a signature reddish tint that makes it look like a twin of the red giant star Aldebaran. The reason Mars looks so rusty-red in the sky has to do with the large amount of rust (iron oxide) that happens be in the planet’s soil. Mars has a very thin atmosphere, about a hundred times thinner than Earth’s, so with few clouds to block the view, we get a pretty nice look at the color of the Martian surface. This planet orbits the Sun in about 23 months and after just a few days you can see its position change in the heavens.

Saturn: Hundreds of times the size of Earth, Saturn is a fast-spinning gas giant. Its rotation rate of only eleven hours creates winds on the planet that blow at over 1,000 miles per hour. Saturn’s atmosphere is mostly hydrogen and helium which helps make it the least dense of all the planets. In fact, if you were to take a fairly good-sized bucket of water and drop Saturn into it, the planet would float! Saturn looks like a bright yellowish star, but its magnificent ring system is visible in binoculars and stand out well in a telescope.

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