You are here

Moon in the Middle

August 31, 2013

The crescent Moon stands at the center of a beautiful triangle at first light tomorrow. The points of the triangle are marked by the planets Jupiter and Mars and the star Procyon.

The brightest point is Jupiter, which stands directly above the Moon. Jupiter outshines all the other planets and stars in the sky at that hour, so it’s hard to miss.

Mars is to the lower left of the Moon. It’s only a few percent as bright as Jupiter, so it’s no spectacle. Its orange color will help you pick it out, though — and so will its lack of twinkling. As a planet’s light travels through the atmosphere, it remains steadier than that of a star.

To see the difference, look to the lower right of the Moon for Procyon, the “little dog” star. It’s brighter than Mars, but it shows no color of its own — it’s pure white. The only color comes from dust and other particles in the atmosphere — the same things that color the Moon when it’s low in the sky — and from Procyon’s twinkling.

A star twinkles because it’s a mere pinprick of light in the dark night sky. As its light travels toward us, it’s bent by different layers of the atmosphere. Different colors of light are bent at different angles, so a twinkling star changes color. And the brighter the star, the more obvious the shift in color.

Mars and the other planets appear as tiny disks, so their light isn’t as distorted by its trip through the atmosphere — allowing our neighboring worlds to shine steadily.


Script by Damond Benningfield, Copyright 2013

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.