Weekly Psalm 19: Supermoon Lunar Eclipse

Here is your weekly reminder of Psalm 19 — a “supermoon” lunar eclipse.

Lunar_eclipse

Last Sunday, many of us were treated to a rare combination of a lunar eclipse and a “supermoon.” A supermoon occurs when a full moon phase coincides with the Moon being at its closest point in its slightly elliptical orbit around the Earth, making our lunar companion look slightly larger (~14% in diameter) in the sky than normal. What really makes a supermoon “super” is its increased brightness — owing to its closeness to the Earth, a supermoon is 30% brighter than a regular full moon.

A lunar eclipse occurs when the Earth moves between the Sun and the Moon, blocking out the sunlight that normally reflects off of a full moon.

2000px-Geometry_of_a_Lunar_Eclipse.svg

When I teach introductory astronomy, the students who are really paying attention will ask why we don’t always get a lunar eclipse during a full moon phase. The answer is, the plane of the Moon’s orbit (outlined with the green circle above) is slightly tilted with respect to the Earth’s orbital plane (outlined in blue), so that most of the time the Earth does not block light coming from the Sun. Rarely, we’ll get the Sun, the Earth, and the Moon lining up when the Moon is in the Earth’s orbital plane, and that’s when we experience a lunar eclipse.

The next time a supermoon will coincide with a lunar eclipse is in the year 2033.

Supermoon lunar eclipse photo credit: Dina Rudick (Boston Globe). Lunar eclipse schematic credit: Wikipedia.

2 thoughts on “Weekly Psalm 19: Supermoon Lunar Eclipse

  1. We took the kids out that night to see the moon. Very different looking :)

    What made is so red, though? Sunlight through the Earth’s atmosphere filtering out wavelengths other than reds?

  2. Yep, that’s the reason. This ‘filtering’ by the atmosphere is really just the scattering of shorter wavelength (bluer) light, leaving the longer wavelength (redder) light to pass through the atmosphere to the Moon.

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