Due to the tilt of the moon’s orbit from the plane of earth’s orbit, there are only two times per year, 31 to 37 days long, when it can cast its shadow on earth at new moon, or pass into earth’s shadow at full moon. Then, and only then, do eclipses occur.

Because these “eclipse seasons” exceed a lunar month, each has two or three eclipses, at least one of which is solar, and one is lunar. Last August’s eclipse season comprised a partial lunar (not visible in Idaho) and the total solar eclipse that wowed America. Half a year later, it’s eclipse season again.

This year’s first eclipse season brings a total lunar for the Pacific Rim, and a partial solar only visible from Antarctica and southernmost South America. The second (mid-July to mid-August) begins and ends with partial solar eclipses framing a total lunar, though none are visible from Idaho.

Next Wednesday morning’s pre-dawn total lunar eclipse is being described as a “super blue blood moon” by media outlets looking to whip up excitement. But “super” moons are hardly unusual (this being the second in 2018 already), and “blue” moons (the second full moon in a month) are curiosities with zero visual or astronomical impact. “Blood moon” is a melodramatic euphemism for a total lunar eclipse, during which the moon takes on a deep red or red-orange hue. That’s what’s worth seeing.

After subtly darkening for nearly an hour, the moon begins its traverse of earth’s dark shadow—the umbra—at 4:48 a.m. Total immersion lasts from 5:52 to 7:07 a.m. and the moon sets while still missing a dark umbral “bite” at 8:01 a.m.

So, next Wednesday morning, set your alarm early, bundle up, and go outside to enjoy the celestial spectacle.

Next column: Is the universe empty or crowded?

Sky calendar through February 7th:


One hour after sunset:

No planets visible.

One hour before sunrise:

Saturn: SE, very low.

Mars: SSE, low.

Jupiter: S, low.

Moon: Full moon 6:27 a.m. 1/31. Close to Jupiter 2/7. Last quarter

8:54 a.m. 2/7.

Chris Anderson manages the College of Southern Idaho’s Centennial Observatory in Twin Falls. He can be reached at 208-732-6663 or canderson@csi.edu.


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