The next full moon is known as the Cold Moon, the Long Night Moon, or the Moon Before Yule. The moon will be “opposite” the sun at 9:38 a.m. EST on Saturday, Dec. 10. The moon will appear full for about three days around this time, from the evening of Thursday, Dec. 8 through the morning — and possibly the evening — of Sunday, Dec. 11.
On Dec.10, the moon will be so “opposite” the sun from the Earth that it will pass through the shadow of the Earth. The Earth’s shadow will begin to reduce the amount of sunlight reaching the moon at about 6:34 a.m. EST, but the U.S. East Coast will not be able to tell that the moon appears dimmer before it sets at 7:08 a.m. EST. The full shadow of the Earth (called the umbra) does not start to fall on the moon until about 7:46 a.m. EST, well after the moon has set for the U.S. East Coast. Even for the U.S. West Coast, the eclipse will be near moonset, making this a difficult eclipse to view. The extended period with reduced sunlight, including 51 minutes in the full shadow of the Earth, presents a challenging environment for spacecraft at the moon (LRO, the twin GRAIL spacecraft) that rely upon sunlight for heat and solar power. Because the two ARTEMIS spacecraft are in highly elliptical orbits around the moon, it is not clear if or how they will be impacted.
Europeans call the December full moon the Moon before Yule. Yule is an old northern European winter festival that is now associated with Christmas. The Native American names for the full moon in December — as reported in the Farmer’s Almanac — are the Cold Moon or the Long Night Moon. The Cold Moon gets its name because December is the month when it really starts to get cold, although our coldest average temperatures are in January. The Long Night Moon gets its name because the full moon in December occurs near the solstice, which has the longest night of the year. The full moon takes a high trajectory across the sky because it is opposite to the low sun, so the moon will be above the horizon longer than at other times of the year.
A full moon over Earth, seen by astronaut Ron Garan from the International Space Station. (NASA)
2 thoughts on “A Shadow on the Moon”
Those are some interesting names for the December Full Moon: the Cold Moon, the Long Night Moon, and Moon Before Yule. It sounds like this Full Moon will occur during a Lunar Eclipse because it was stated the Earth’s shadow will begin to reduce the amount of Sunlight that reaches the Moon, which will result in a distortion of the Moon’s apparent figure/shape, to the point where the Moon will not be visible in the sky. Why exactly is the shadow of the Earth called the umbra? Is it because the Earth acts as an umbrella for the Moon, shielding it from the light of the Sun.
It was stated in the blog post the extensive period of shadow will present a challenging environment for the spacecraft at the Moon because they rely in the Sunlight for heat and solar power. Could this also mean the spacecraft will struggle to operate during other activities? Is/are there any other method(s) of supplying heat to the spacecraft? Is/are there any other method(s) by which the spacecraft can operate without solar power? If not, it seems like this should be something to consider to eliminate malfunctions during situations like this.
To answer your questions…
1) Why exactly is the shadow of the Earth called the umbra?
Because the Earth will reside completely within the shadow cast by the Moon. Umbra means “shadow” in Latin, whereas Penumbra means “Almost shadow” in the same language.
2) Could this also mean the spacecraft will struggle to operate during other activities? Is/are there any other method(s) of supplying heat to the spacecraft? Is/are there any other method(s) by which the spacecraft can operate without solar power?
Lunar eclipses are easily predictable and are taken into account in spacecraft operations. While in shadow, most spacecraft draw power from their batteries, which are designed provide electricity during any eclipses which may occur during the spacecraft mission. Electricity powers the thermal systems to keep the spacecraft warm during shadow periods.
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