I know you’ll all be out there moon gazing tonight in celebration of International Observe the Moon Night. You can use the photo and key above to help you identify some of the gibbous moon’s most prominent features. The seas or “maria” (MAH-ree-uh) are visible with the naked eye, while sharp-eyed sky watchers can pick out the larger rayed craters like Copernicus and Tycho. All the other features are visible in binoculars and small telescopes.
* 1-6: The maria are ancient impact basins created when asteroids struck the moon some four billion years ago. At that time, they looked like enormous craters, but lava from the mantle bubbled up through cracks and later filled them.
* A: Copernicus is 58 miles across and one of the most magnificent lunar craters. It looks like a bulls-eye surrounded by its bright rays of ejecta.
* B: Kepler is similar to Copernicus in appearance but smaller.
* C: Sinus Iridium or Bay of Rainbows is a large crater, the right half of which was flooded by Mare Imbrium lavas. As a result, we see only half the crater which resembles a bay.
* D: Plato is 68 miles across and a nice even gray color. It’s also been flooded by lavas from within, making it look like a miniature lunar sea.
* E: Gassendi crater is the same size as Plato. Its proximity to the moon’s day-night line, called the terminator, will bring its walls, rough interior and central peak into beautiful relief tonight.
* F: Tycho is 53 miles in diameter and one of the freshest, large lunar craters. Its extensive system of rays has no equal on the moon.
* G: Proclus is a small crater with a brilliant, asymmetric ray system.
* H: Langrenus, at 84 miles across, looks like a smooth white oval. Its “flat” appearance is due to lack of shadows (which show relief) from a high sun.
* I: Directly below or south of Tycho, you’ll see Clavius, one of the largest craters on the near side of the moon. It’s 140 across and home to lots of additional craters within its walls.
* J: The arc-shaped Apennines Mountain range lies along the southeastern border of Mare Imbrium. Peaks here reach to 2.8 miles.
Jupiter quickly catches the eye low in the southeastern sky after 9 o’clock. There’s nothing else that comes close to its brightness in that region. Binoculars will not only show several of its brightest moons, which happen to be lined up left-to-right in order of increasing true distance from the planet, but also the planet Uranus. It’s the “star” directly above Jupiter and about as bright as the moon Io. Jupiter and Uranus are in conjunction with each other tonight and less than one degree apart. If you’re using a small or medium-sized telescope at its lowest magnification, both planets will fit comfortably in the same field of view. As you look at the pair, consider that Jupiter is 367 million miles from Earth, while Uranus is deep in the background at 1.8 billion miles or four times as distant.
Above the moon, stands the Summer Triangle, composed of the three luminaries Deneb, Vega and Altair. Vega is the brightest and will occupy the sky’s overhead spot called the zenith around 8:30 p.m.
The west-northwest is not without its celestial booty. Find the Big Dipper, which is leveling out low in the northwestern sky at nightfall, and follow the arc of its handle to the brilliant, papaya-colored Arcturus. No matter where you look tonight, there’s something for the eye to marvel upon.
As a reminder, members of the Arrowhead Astronomical Society will have telescopes set up for looking at the moon and Jupiter in Canal Park in Duluth – weather permitting – between 8 and 11 tonight. Look for us near the Lakewalk at the east end of the parking lot. See you there.