Full Flower Moon Knows No Borders

A full moon rise over Lake Superior seen from Canal Park in Duluth, Minn. Credit: Bob King

Guess what’s blooming in the east around sunset tonight? A most unearthly flower better known as the moon. Tonight’s the full moon and one with a name we can relate to. Flowers may show in March and April but by May, the gang’s all here. Our local bloomery includes bloodroot, violets, marsh marigolds and the sunny-faced dandelion.

The Full Flower Moon will shine from Libra the Scales tonight. Stellarium

The moon has slid to the south since winter, lingering tonight in the constellation of Libra the Scales, the only constellation in the zodiac named for an inanimate object, the scales or balance. All the others are either animals or mythological creatures. The Babylonians of 1000 B.C. knew Libra’s stars as ZIB.BA.AN.NA, the balance of heaven. Back then, Libra marked the location of sun on the first day of fall or autumnal equinox , when days and nights were “balanced” or equal in length. Because of precession, a cyclic wobble of Earth’s axis that causes the sun to slide westward through the zodiac, the equinox sun now shines in Virgo, one constellation to the west of Libra.

You won’t see much of Libra tonight because the moon’s so bright. It reaches its peak magnitude around –14, making it about one million times brighter than a typical bright star (first magnitude). No wonder we see so few stars on full moon nights.


Precession of the Equinoxes Explained or click here for more information

We all know the moon orbits the Earth, so it’s in constant motion, moving to the east at the rate of one of its diameters per hour. In 24 hours that’s 24 moon-widths or 12° — a bit more than a fist held at arm’s length against the sky. Tomorrow night, the moon will appear a fist to the left (east) in the constellation Scorpius the Scorpion. It’s fun and instructive to follow the moon: not only do you get familiar with its gait but also its changing phase and rising and setting times.

In this wider view, we see how the constellations have precise borders and interlock like a jigsaw puzzle. The borders were established in 1930. Stellarium

As you can see, no border wall can contain the moon, which freely crosses from one constellation to the next. Those sharp-cut property lines were created in 1930 by the International Astronomical Union to help define the limits of each of the 88 constellations. Before that time, different star atlases featured their own take on borders, making it hard for astronomers to agree on what constellation a particular star belonged to.

Watch for tonight’s full moon to rise with Earth’s shadow, the gray band seen just over the lake in this photo. The red top of the band is light from the reddened sun reflected back by air high in the atmosphere. It has a wonderful name: the Belt of Venus.  Credit: Bob King

The Flower Moon will rise simultaneously with Earth’s shadow in the eastern sky around sunset directly opposite the sun. The shadow is a darker, gray-purple band spanning the entire eastern horizon that appears first right around sunset and fades into the gathering darkness 20-25 minutes later. Earth casts a shadow just like we do, and it darkens the twilight atmosphere as our shadows darken the ground. It’s visible from about sunset till about 20 minutes after.

European skywatchers get to see the Flower Moon a few hours earlier than those in the Americas. This gorgeous photo was taken just a short while ago over the Adolfturm in Friedberg, Germany. Elvis Presley lived here for some time when he served in the Army from 1958-1960. Credit: Ulrich Beinert

To see all the wonders of the Flower Moon moonrise be sure you’re out in time. Click here to find out when the moon rises from your town.