The Moon was officially full at 12:40pm MDT on Thursday June 24th. At that time, the Sun, Earth, and Moon were aligned, with Earth in the middle. Because the Moon was near perigee in its orbit around Earth (‘perigee’ is the term used to describe an orbiting object’s closest approach to the object it orbits), it appeared slightly larger than average – hence the misleading name, ‘supermoon.’
The term ‘supermoon’ was actually coined by an astrologer. But, there’s nothing super about a supermoon, at least from an astronomical perspective. In fact, you wouldn’t know you were looking at a supermoon, unless somebody told you so.
The media likes to use terms like ‘supermoon’ to generate interest and excitement. They called the January 2019 total lunar eclipse, the ‘Super Blood Wolf Moon’ because it was a) a supermoon; b) an eclipsed moon, in which the Moon appears reddish; and c) some Native American tribes refer to the January full moon as the ‘Wolf Moon’ because hungry wolves are said to howl more on cold winter nights.
Personally, I think the hype does astronomy a disservice since it encourages people to go out and look at the night sky, thinking they’re going to see something really different and exciting, but come away disappointed because the Moon didn’t fill half the sky or rise dripping in blood.
OK, back to this week’s supermoon. Because the Moon was full at about midday on Thursday, it appeared to be virtually full on both Wednesday and Thursday evenings. Wednesday evening was pretty cloudy, but I managed to photograph the Moon through a large rift in the clouds.
When the Moon is full, there’s little detail to be seen on the surface, due to the lack of shadows. The full moon is beautiful to the unaided eye, but doesn’t show much more than light and dark patches, even in a telescope.
The light patches are called the ‘lunar highlands’ – these are geologically old surface materials (mainly igneous rock), which are heavily cratered.
The dark patches are known as ‘lunar maria’ or ‘lunar seas’ – the result of lava flows. Because the lava flows are more geologically recent than the lunar highlands, the maria are lightly peppered with craters, as compared to the heavily bombarded highlands. Many of the lunar maria appear round – this is due to lava flowing into and filling ancient impact basins.
In the attached photo taken on Wednesday, about 16 hours before full, you can see a little bit of relief along the lower left limb since there’s a just a sliver of night at the very edge. The rest of the Moon seems flat and featureless, although the maria and highlands are obvious due to their differences in brightness and color.
One exception is the bright, rayed crater, Tycho, easily seen at the lower right. Tycho’s 53-mile-wide crater was formed about 100 million years ago – likely the result of impact with an asteroid. Ejecta from the impact was blown across the surface of the Moon, creating the bright rays we see today. The longer rays are over 900 miles long.
The Moon, photographed on Wednesday night, about 16 hours before full.
Contrast Wednesday’s photo of the Moon (above) with the photo taken on Thursday, about ten hours after full (below). The lower left limb is now devoid of relief; the only visible surface detail is along the upper right limb. This is due to the fact that the Moon is now waning (past full). The sunrise terminator we saw before full has now moved beyond the visible portion of the Moon. But, the sunset terminator is now beginning to stretch along the right edge.
The Moon, photographed Thursday night, about ten hours after full.
Finally, check out the photo of the Moon below, taken Friday, about 35 hours after full moon. The sunset terminator has shifted to the west, compared to the Thursday photo, and the waning gibbous moon has taken on a slightly oval shape. Relief is obvious now, with numerous, shadow-filled craters spread along the upper right limb. The terminator provides the contrast of light and shadow, turning seemingly uninteresting markings into stark, three-dimensional relief.
The Moon, photographed Friday night, about 35 hours after full. The bright eastern crater walls along the sunset terminator at the upper right catch the last rays of the Sun, while the crater floors are filling with shadows created by the western walls.
The Moon, our closest neighbor, is often overlooked by those seeking planets and deep sky objects. It’s even seen as a nuisance, spreading light into the night sky, making it more difficult to view everything from star clusters and nebulae to meteors. I know the Moon is sometimes seen in a bad light (excuse the pun) because I sometimes fall into this trap.
But, the Moon is actually a never-ending source of interest and fascination, even in binoculars and small telescopes. If you focus on the terminator, you’ll see new features every night that may have escaped your eye the night before. So, embrace the Moon and marvel in its ever-changing face.