A view of the full moon created from images taken by NASA’s Lunar Reconnaissance Orbiter. The full moon is coming up on Sept. 2. Although beautiful to look at, you can get a better view of its many surface features later in the month as the moon progresses through its phases. Photo courtesy of NASA/GSFC/Arizona State University
Everyone talks about the full moon. It appears big and bright as it rises in the night sky, and it stays there all night. Plus, it can pass through the shadow of the Earth, creating lunar eclipses. However, the full moon gets all the attention while the other phases get short shrift.
The full moon only occurs when the moon is opposite of the sun in our sky. As it moves in its orbit around the Earth, the sun illuminates different parts of the moon. The apparent changing shape of the moon is known as its phases. The moon completes its orbit about once a month, and so the phases repeat every 29.5 days.
Although the full moon is bright and looks pretty in the sky, it is actually not the best time to view its surface. When it is full, the sun’s light is falling directly onto the moon’s surface. If you look at it with a telescope, the surface appears somewhat flat. It also can be painful to look at in a telescope because of the brightness. You can use a filter to make viewing a little more comfortable, but if you really want see some good detail, it is best to look at the moon either before or after it is full.
One of the best times to look at the moon is when it is near first quarter. This shows craters, maria, mountain ranges and the numbers correspond to Apollo landing sites. Note that in a telescope these features will appear upside-down. Photo courtesy of NASA/GSFC/Scientific Visualization Studio
The best time to view the moon in binoculars or a telescope is either near first quarter or last quarter. During those phases, sunlight is hitting the surface in such a way that show’s some of the moon’s features. Craters, valleys and mountains are lit up as the sunlight creeps across the lunar surface. This illumination really gives the moon a 3D appearance that is breathtaking on a clear night.
This constant motion of the moon means the time you can view is changing from night to night. As a good rule of thumb, the moon is rising, on average, about 50 minutes later than the night before. At the beginning of the cycle of phases, the thin crescent moon is visible after sunset. At first quarter, it is visible in the early evening. The full moon rises at sunset and remains visible all night until sunrise. The last quarter moon doesn’t rise until the early morning hours, and the crescent moon is visible at sunrise. Finally, the new moon occurs. This is when the night side of the moon is facing us, so we don’t see it at all. The cycle of phases starts again thereafter.
This can be confusing because you have two motions happening at the same time: the moon is moving west westward through the sky due to the Earth’s spin but it also is slowly creeping eastward due to its motion in orbit around Earth. To help keep track of the moon you can use an app or visit the NASA Dial-A-Moon website.
Kevin D. Conod is the planetarium manager and astronomer at The Newark Museum of Art’s Dreyfuss Planetarium. For updates on the night sky, call the Newark Skyline at (973) 596-6529.
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