I’m not sure if Van Morrison had this in mind when he came out with “Moondance” in 1970, but on Monday and Tuesday the new crescent moon will be dancing between some planets and one moderately bright star toward the end of evening twilight in the low western sky. You make sure to do your own “clear-sky” dance, so you won’t miss one of the best sky shows of 2007.
The moon’s dancing partners will be the very bright planet Venus, the dimmer but lovely planet Saturn, and Regulus, the brightest star in the ancient constellation Leo. All three have been doing their own celestial tango in the early evenings for the last several weeks, and Saturn and Venus drew within a degree of each other the last week of June. Since then they’ve parted intimate company, but they’re still fairly close to one another in the sky. Right now Venus is having a closer celestial hug with the star Regulus, separated by just over two degrees, or about the width of two of your fingers held at arm’s length.
All this celestial dancing and conjunctions among Venus, Saturn and Regulus are compliments of the differing orbital speeds of our Earth, Venus, and Saturn. What makes it extra interesting is that all of the planets in our solar system orbit the sun in nearly the same plane, so on a regular basis the planets can appear to be really close to each other in the sky. Of course, they’re just in our same line of sight from our vantage on Earth.
On Monday night, the 38th anniversary of the launch of Apollo 11, first manned mission to the moon, the very thin crescent moon will be practically touching Saturn, about a degree to the left of the ringed wonder of our solar system. You don’t need a telescope to see this conjunction, but if you do have access to a small scope or even a decent pair of binoculars, I know you’ll like what you’ll see.
Just off the right limb of the moon will be Saturn. It will definitely be a fuzzy view of Saturn, because the planet is so close to the horizon that its light has to plow through a lot more of Earth’s atmosphere than it does when it’s higher in the sky. In addition, Saturn is nearly at its maximum distance from the Earth, more than 900 million miles away. It’s still worth a look though, especially when you realize that the diameter of Saturn’s ring system is more than 136,000 miles, more than half of the distance from Earth to our moon. Early this week, the moon is just over 240,000 miles away.
On Tuesday night, the crescent moon will be a little fatter and will have shifted to the east, placing it just to the left of Venus and Regulus. With binoculars or a low power telescope you may be able to get the moon, Venus and Regulus in the same field of view. One thing you’ll notice right away is that Venus, just like the moon, is crescent shaped. Because Venus’s orbit lies within the Earth’s orbit around the sun, and because the only light we see on planets is reflected sunlight, Venus changes shapes just like our moon, depending on where the Earth and Venus are in their respective solar orbits.
Venus is so much brighter than Regulus, mainly because it’s a whole lot closer and its thick cloud cover is a very good reflector of sunlight. Right now Venus is about 39 million miles away, and Regulus is more than 465 trillion miles away. Even though Regulus is the dimmest of the participants in our “moondance” early this week, it’s by no means a wallflower. This 4-million-mile-wide star is more than four times the diameter of our sun. It also kicks out nearly 200 times more light than our home star.
One more thing, if atmospheric conditions are right, we may see what’s known as Earthshine on the moon. It can be an absolutely wonderful sight. Because of sunlight bouncing off the earth and onto the moon, we can sometimes see the entire disk of the moon when it’s in crescent phase. The crescent part of the moon is because of direct sunlight and the rest of the moon’s disk is “second hand” sunshine reflecting off our Earth and onto the moon.
Enjoy the dance this week. All you have to do is take a minute to look up.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and author of the new book “Washington Starwatch,” available at bookstores and on his Web site, www.lynchandthestars.com.
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