Earth & Sky

Tonight’s moon is still near the star Antares in the constellation Scorpius. It’s a bright red star known for twinkling rapidly. If you have binoculars, sweep for an object near Antares on the sky’s dome. This object is called M4, and it’s a globular star cluster located just one degree to the west of Antares.

After sunset today, according to U.S. clocks, our planet Earth will reach its most distant point from the sun for this year. Astronomers call this point “aphelion,” and, at aphelion we’re about three million miles farther from the sun than we will be six months from now. Our average distance from the sun is 93 million miles.

Tonight’s moon appears near the upper part of the constellation Scorpius. These three stars are sometimes called ‘the Crown of the Scorpion.’ Individually, the Crown stars are Graffias, Dschubba, and Pi Scorpii.

Tonight’s moon – in front of the constellation Libra – arcs across the south throughout the night. As seen from the northern hemisphere, the moon can be in the east, south or west, but not due north. The moon follows more or less the same path that the sun does each day. You know how the sun shines in your south windows, but not your north windows? Likewise, you’ll never be kept awake by a moon shining low and due north.

If you noticed the moon last night, you might also have noticed the star Spica was to the left of the moon. Tonight, Spica is to the moon’s right. This motion of the moon on our sky’s dome is due to the moon’s actual motion in orbit around Earth.

Spica is that bright star in the southern heavens just as it gets dark tonight. The waxing gibbous moon is a bit off to the right (west). Our view of the moon is less than a second and a half old, but the light from Spica left the star 260 years ago.