An Arch of Planets

Hi everyone,

Just a quick note this time. Sadly I have nothing to report about the recent Perseids, because there were clouds where I live. Hopefully you had better luck observing them than I did.

Today I just wanted to point out the arch in the southern evening skies. Several planets and the moon are lined up in a nice row, giving us another opportunity to visualize the solar system in the night sky.

If you face south (assuming you live in the northern hemisphere) about an hour after sunset tonight, you may be able to see a few remaining rays of light over the horizon where the sun recently set. Venus is now well established above the sunset as the beautiful “Evening Star”, and to the left of Venus will be the star Spica, the brightest star in the constellation Virgo. To the left of Spica will be the moon, marking south and currently passing through the lovely pair of Scorpius and Sagittarius. To the left of the moon will be two more bright dots: Saturn and Jupiter. Perhaps you remember that Saturn passed through “opposition” in early August, and Jupiter will be passing through opposition in only a few days, on the 19th-20th, meaning that right now it very nearly marks the point in the sky exactly opposite to the sun. If you imagine the sun below the horizon, and then trace out the imaginary curve from the sun through Venus, Virgo, Scorpius, the Moon, the teapot of Sagittarius, Saturn, and finally Jupiter and the point of opposition, you will have traveled half of the circle of the Zodiac, or half of the Solar System.

The moon has been marching eastward along that path and it will continue to do so as the days go by. Apart from the moon, the rest of the scene should be pretty much identical for the next week or so, and you may enjoy keeping track of the moon over the coming days as it marches down the “highway” of the zodiac, reaching Jupiter and opposition, and thus becoming full, on the 22nd.

If you live in the southern hemisphere, you should be able to see the same arch, except it will be upside-down and backwards in the northern sky instead of the southern, with the sunset on your left and Jupiter on your right as you face north.

That's all for now!

John