Enjoying EarthSky? Subscribe.

265,797 subscribers and counting ...

Last quarter moon on March 9

It’s also very near Mars, and 2 other planets. When to watch for it, what to look for.

The moon was almost exactly at last quarter when Jenney Disimon in Sabah, North Borneo, captured this photo. The terminator line, or line between light and dark on the moon, appears straight.

Before sunrise on March 9, 2018, the moon will be at or near its last quarter phase. A last quarter moon always rises in the middle of the night, appears at its highest in the sky around dawn, and sets around midday. At last quarter, the lunar disk appears half-lit in sunshine and half-immersed in the moon’s own shadow. The lunar terminator – the shadow line dividing day and night – shows you where it’s sunset on the lunar terrain.

The March 9, 2018 last quarter moon will be near the red planet, Mars.

It’ll also be in the neighborhood of a red star Antares, brightest star in Scorpius the Scorpion. You can distinguish Mars from Antares because the red planet shines a bit more brilliantly than Antares now. Also, since Mars is a planet, it might be shining with a steadier light than sparkly Antares.

Plus Jupiter and Saturn are also part of the scene, on these mornings around March 9. Read more.

Get up before dawn for a great view of the moon and the morning planets! On the morning of March 9, the last quarter moon is near Mars.

The moon reaches its last quarter phase on March 9 at 11:20 UTC (translate UTC to your time). At North American and U.S. times zones, that places the time of the last quarter moon at 7:20 a.m. AST, 6:20 a.m. EST, 5:20 a.m. CST, 4:20 a.m. MST, 3:20 a.m. PST, 2:20 a.m. Alaskan Time and 1:20 a.m. Hawaiian Time.

The last quarter moon is synonymous with the moon at western quadrature, or 90 degrees west of the sun. Want to know if the moon is at western quadrature right now? Click here and scroll down to Moon Sun Elongation. If the elongation is -90o, then the moon is at western quadrature (last quarter). If the number is larger (for instance, -91o), then the waning moon is not quite yet at western quadrature; if the number is smaller (-89o), then the waning moon is a little past western quadrature.

Not only the moon, but any celestial object is said to be at western quadrature when it’s 90 degrees west of the of the sun in Earth’s sky. Because Mars will be about 6 degrees east of the last quarter moon on March 9, 2018, Mars will also be about 84 degrees west of the sun on that date. However, the red planet’s angular distance west of the sun is now increasing by about 0.4 degrees daily. So Mars will reach western quadrature on March 24, 2018. Read more.

Zefri Besar caught this last quarter moon just after midnight, from Brunei Darussalam.

A last quarter moon provides a great opportunity to think of yourself on a three-dimensional world in space. For example, it’s fun to see this moon just after moonrise, shortly after midnight. Then the lighted portion points downward, to the sun below your feet. Think of the last quarter moon as a mirror to the world you’re standing on. Think of yourself standing in the middle of Earth’s nightside, on the midnight portion of Earth.

Also, a last quarter moon can be used as a guidepost to Earth’s direction of motion in orbit around the sun.

In other words, when you look toward a last quarter moon high in the predawn sky, for example, you’re gazing out approximately along the path of Earth’s orbit, in a forward direction. The moon is moving in orbit around the sun with the Earth and never holds still. But, if we could somehow anchor the moon in space . . . tie it down, keep it still . . . Earth’s orbital speed of 18 miles per second would carry us across the space between us and the moon in only a few hours.

A great thing about this observation is that it can be done from anywhere. Ben Orlove wrote from New York City: “I was sitting in the roof garden of my building, and there was the moon, right in front of me. You were right, this is a perfect time to visualize … the Earth’s motion.”

Four keys to understanding moon phases

Bottom line: The March 2018 last quarter moon – on the morning of March 9 – will be near the planet Mars in the sky. Plus, 2 other planets are nearby.

Deborah Byrd