The Moon and planets for September 2010
Venus and Mars are prominent in the western sky during September, and Jupiter is shining away in the eastern sky. Saturn is low in the western sky after sunset, and sinks lower and lower as the days go past. By the end of the month it will have dipped below the horizon and we’ll have to wait until later in the year for it to make its reappearance. Unfortunately, Mercury is lost in the glare of the Sun this month.
The Moon will be near the star cluster known as the Pleiades, in the constellation Taurus. You’ll have to be up early though, as this takes place in the early morning hours. By tomorrow morning (Sep 2), the Moon will have moved along a bit in its orbit and it will no longer appear next to the cluster.
The Pleiades is also known as the Seven Sisters, as people with average eyesight can usually make out seven of the stars with the unaided eye (from a reasonably dark location of course; not standing under a streetlight). Some people with really good eyesight can make out a few more.
In fact, the Pleiades has hundreds of stars, as shown by the beautiful image at right. You’ll also see that it seems to have a lot of wispy gas clouds too. Well, the gas and the stars are not actually connected, although they are in the same region of space. The stars are actually slowly passing through the gas clouds as a bunch, and we just happen to be living at the right time in history for us to see them together like this.
By the way, the next time you see a Subaru car drive past, take a look at the brand badge on the grill—you’ll see that it is a group of stars. Subaru is the Japanese name for the Pleiades!
Tonight is Last Quarter Moon, which is halfway between Full Moon and New Moon.
Before sunrise, the Moon will seem to be sitting above (or below, for Northern Hemisphere stargazers) two reasonably bright stars. These are Castor and Pollux, the twin stars of the constellation Gemini.
Tonight is New Moon, which is halfway between Last Quarter and First Quarter.
Also tonight, the Moon will be at its closest to Earth for the current lunar orbit, being 357,191km away. The Moon travels in an elliptical orbit, so sometimes it is closer and sometimes it is further away. When it is at its closest, like tonight, we say it is at “perigee”. The furthest point is called “apogee”, and this month it will occur on the 21st.
For Southern Hemisphere stargazers, if you look out to the west after sunset, you’ll see the crescent Moon just near what looks to be a reasonably bright star. In fact, it’s the famous ringed planet Saturn. If you have a small telescope, or know someone who does, take a look—you should be able to see its rings slightly tilted, and you should also be able to make a few of its moons.
Tonight, the thin crescent Moon will appear to hover right between Mars and Venus. It’ll be a really beautiful sight. And it’ll be easy to tell which planet is which—Venus is much brighter and a whitish colour; Mars is dimmer and a ruddy orange colour.
The star Spica (the brightest star in the constellation Virgo) will be nearby too.
At this time, the Moon will have just passed its “new Moon” phase—the opposite of full Moon—and will be heading toward first quarter on the 15th.
The Moon will appear close to the star Antares, the brightest star in the constellation Scorpius (often called Scorpio). Antares is a huge, red supergiant star. If you compare the colouring between Antares and the planet Mars, you’ll see that they are very similar. And that’s how Antares got its name—the ancient Greek name for Mars is Ares, and Antares means “rival of Mars”.
Tonight is First Quarter Moon, which is halfway between New Moon and Full Moon.
The Moon is at apogee today (see note for Sep 8), at a distance of 406,167km.
The planet Jupiter is at opposition. This means that the Sun and Jupiter are on exactly opposite sides of the Earth…the Sun one way, Jupiter exactly 180 degrees the other way.
The upshot of this is that as the Sun sinks below the horizon in the west at sunset, Jupiter rises over the horizon in the east. This means that the planet will be in the sky the whole night, from sunset through to tomorrow’s sunrise, giving you a full night to observe it.
The time of a planet’s opposition usually is very close to another milestone…it’s closest approach to Earth during that particular orbit. And when a planet is at its closest, it looks bigger through a telescope and therefore better studies can be made of it.
So putting the two together, opposition and closest approach, and you can see why astronomers look forward to these times to do their observations.
It’s Full Moon tonight! As the Sun goes down in the west, the Moon will rise over the eastern horizon. And you’ll see a bright looking “star” nearby—that’s not a star, it’s actually the planet Jupiter. If you have a medium sized pair of binoculars, or a small telescope, take a look at the giant planet—you should be able to see from one to four of its largest moons, and with a telescope you should be able to make out some of its atmospheric “bands”. Jupiter’s four largest moons are called the Galilean moons, after Galileo who first saw them just over 400 years ago.
It’s also the Equinox today—the Spring Equinox for those in the Southern Hemisphere, and the Autumn or Fall Equinox for those in the Northern Hemisphere.
The Equinox means that the Sun “crosses” the celestial equator, at this time of year going from north to south, heralding the coming of Spring in the Southern Hemisphere and Autumn or Fall in the Northern Hemisphere.
In reality, the Sun isn’t moving—it’s the combination of the Earth’s tilt and the position of the Earth in its orbit that makes the Sun appear to move north and south in the sky during the course of the year.
Twenty-eight days since it was last there (see Sep 1), the Moon will be back near the Pleiades star cluster in the constellation Taurus. But it won’t be in exactly the same position—this time, it’ll be nestled between the Pleiades and red Aldebaran, the brightest star in Taurus.
If you have any questions or comments on the night sky, please use the feedback form below. Happy stargazing!
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