Spotting the New Moon
On Thursday evening, August 20, the 15-hour-old moon is actually lower in the sky than the sun. Note the shallow angle which the ecliptic makes with the horizon and that the moon is well south of the ecliptic.
Credit: Starry Night® Software

In ancient times, the first sighting of the new moon each month was an important marker on the calendar. Even today, many religions base their feasts and festivals upon the appearance of the new moon.

Except when there is a solar eclipse, the new moon is not actually visible or observable, because it is so close to the sun in the sky, and backlit as well.

Last month, new moon fell on July 22, and the moon was exactly in between the sun and the Earth, so that its shadow fell on the surface of the Earth, causing a solar eclipse widely observed in India and China. This month, new moon falls on Aug. 20 at 10:02 Universal Time (6:02 a.m. Eastern Daylight Time).

The time of new moon is determined by the geometry of sun, moon and Earth, and takes place at exactly the same moment everywhere on our planet, although the local time depends on your time zone. This month the moon is well south of the line joining the sun and Earth, so there is no eclipse.

Most of the time, the closest we can get to observing the new moon is on the first evening or two after the exact date and time of new moon, after the sun has set but before the moon sets.

This month, a strange thing happens on the first evening after new moon.

Even though it?s more than 15 hours past new moon, the moon is actually lower in the sky than the sun. In Starry Night we can see why this happens. First of all, in August, the ecliptic (the line the sun and planets follow through the sky) is always at a very shallow angle to the horizon. Secondly, the moon?s orbit is not quite in the same plane as that of the Earth, so the moon spends part of the time above the ecliptic, part of the time below. Currently the moon is low to the ecliptic, whereas a few months ago it was high at this time of the month. The combined effect makes the moon low in the evening sky in August and high in the evening sky in April.

The appearance of the moon is affected by the angle at which the sun illuminates it. This month, its position not much higher in the sky than the sun means that its crescent is almost vertical, with its cusps pointing away to the east, away from the sun as always. Back in April the moon was almost directly above the sun and lit from below, so that the cusps pointed straight up from the horizon.

Whenever the moon is in one of these extreme positions, people always ask astronomers if there is something ?wrong? with the moon. They don?t realize that the moon is simply obeying simple rules that they are unaware of.

Back to spotting the new moon this month. If on Thursday night the moon is lower than the sun, there?s no way that we can see it. But on Friday night, the moon has moved farther away from the sun. It?s still low in the sky, but now it?s higher than the sun, so there?s a good chance you can spot it if you have a clear western horizon. Look above and to the left of the sun as soon as the sun dips below the horizon, and, with a little luck, you should spot the moon.

A thin crescent moon is always accompanied by the ?the old moon in the new moon?s arms?: the ghostly full disk of the moon illuminated by earthshine, sunlight reflected from the earth. This is readily visible with binoculars, but usually visible with the naked eye too, if the sky is clear near the horizon.

If you spot the moon, be sure to look just above it to see if you can also see the planets Mercury and Saturn.

If you don?t manage to see the moon Friday night, try again on Saturday. By then it should be an easy object. Either way, you will have seen the moon as a very thin and beautiful crescent.

This article was provided to SPACE.com by Starry Night Education, the leader in space science curriculum solutions.