The Moon reaches Last Quarter this morning, offering excellent views of several features in the lunar west.
The Last Quarter Moon makes it easy to find Grimaldi, a standout smooth, dark crater near the western limb of the Moon. Credit: NASA’s Scientific Visualization Studio
Last Quarter Moon occurs at 7:59 A.M. EDT. This phase of the Moon offers observers a chance to focus on our satellite’s western limb, including the huge, dark Ocean of Storms that stretches more than 1,600 miles (2,500 km) and is prominent in the lunar southwest.Â
A much smaller but nonetheless noticeable dark feature southwest of the Ocean of Storms and near the western limb is the crater Grimaldi. Stretching nearly 140 miles (122 km) across, Grimaldi’s smooth, flat floor lies above a so-called mascon, or concentration of mass beneath the lunar surface, of the sort often found beneath its larger, lava-covered maria. Use a telescope to scan the crater’s floor and look for subtle features such as mounds and ridges, which can be a fun challenge to pick out through the eyepiece.
Not far south of Grimaldi is a crater that appears its opposite: the bright, rayed crater Byrgius. A much smaller 54 miles (87 km) across, Byrgius’ floor is pocked with numerous small craters. The bright ray system actually emanates from Byrgius A, a smaller crater overlapping the larger main Byrgius’ rim, indicating the former came much later in cosmic time. Â
Sunrise: 5:40 A.M.
Sunset: 8:13 P.M.
Moonrise: 1:59 A.M.
Moonset: 12:45 P.M.
Moon Phase: Waning crescent (48%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.
For a look ahead at more upcoming sky events, check out our full Sky This Week column.Â
