The crescent moon shines close to Mars above the western horizon at sunset on Sept. 24, but you'll need to be quick to spot the red planet before it slips swiftly from view alongside the twinkling stars of the constellation Virgo.

Look to the west in the half-hour following sunset on Sept. 24 to see the 10%-lit form of the waning crescent moon hanging 10 degrees — approximately the width of your outstretched fist — above the horizon, with Mars shining a little over 5 degrees to its upper right.

The red planet owes its distinctive hue to an oxidizing process that rusts iron present in the rocks and dust of Mars. This rust-laden dust gets kicked up into the martian atmosphere, making it appear red from afar.

Both the moon and Mars will disappear below the horizon just one hour after sunse

See Full Page