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Mike Kristosik

January is a busy month for astronomy. We’ve got two full moons in the same month and a total lunar eclipse.

With two full moons in one month, the second full moon is also known as a blue moon. January started with the first full moon of the year (supermoon) and will end with the second full moon (a slightly lesser supermoon) of the year.

What exactly is a supermoon? Well the moon’s orbit is slightly elliptical, which means sometimes it is closer to the Earth than at other times in its orbit. This means that the moon's distance can vary from 222,000 (perigee) to 252,000 (apogee) miles from the Earth. The January 1 full moon was "super" because it was within 5 hours of perigee (closest to Earth).

("Supermoon" isn’t an official term. It was coined by astrologer Richard Nolle, in 1979. The technical term is "perigee syzygy of the Earth-Moon-Sun system.")

The second full moon of January won’t be as super, because it will be closest to Earth (perigee) on January 30, about a day before the moon is full on January 31. Because of two full moons in January, there won’t be a full moon in February. Don’t despair, however: March will have two full moons (March 1 and 31).

The moon's orbit is not only elliptical, it is also slightly inclined (5.1 degrees) to the orbit of the Earth around the sun. This is why we don’t have a lunar or solar eclipse every month. There are only two points, called nodes, at which an eclipse can occur. The moon was at one of these nodes during the total solar eclipse of August 21, 2017. On that day the sun, Earth and moon were aligned such that the moon could cast its shadow on the Earth.

On January 31, the moon is going to be at another node and we are going to get to observe a total lunar eclipse when the moon will travel into and through the Earth’s shadow. The sun, Earth and moon will again be aligned; only this time it is the Earth’s turn to cast its shadow on the moon. Since the Earth is so large compared to the moon, the latter will be completely covered in its shadow.

The January 31 total lunar eclipse will be early. Look fairly low in the west to find the moon. It enters the penumbra (partial shadow) at 2:50 a.m. Pacific. The partial phase (when the moon enters the umbra, full shadow) begins at 3:48. Totality begins at 4:51 and ends at 6:08. This gives us a rather lengthy 77 minutes of totality, a far cry from the total solar eclipse last summer. The partial eclipse will end at 7:12.

Resource: HVA club

Heart of the Valley Astronomers is a group of amateur astronomers dedicated to sharing our passions for the night sky with the local communities in the central Willamette Valley of Oregon.

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We meet on the second Tuesday of each month at the Walnut Community Room located the Scott Zimbrick Memorial Fire Station No. 5, 4950 NW Fair Oaks Drive in Corvallis. Our next meeting will be at 7 p.m. Tuesday, February 13. Meetings are free and open to everyone.

We also regularly schedule star parties, technical assistance, astronomy classes through Corvallis Parks and Recreation, and educational outreach for public and private groups. For more information see www.hvaastronomy.com, or look us up on Facebook.

Question of the Month

Last month: In which constellation is the famous Horsehead Nebula located?

Answer: Orion.

This month: When is the Earth farthest from the sun?

Mike Kristosik is a member of Heart of the Valley Astronomy Club.


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