[STARGAZING] A Red Blue Moon

The full moon is the center of attention for a number of reasons in the new year. There are two full moons in January, on the 1st and on the 31st. Having two moons in one calendar month happens on the average every 2½ years, and results from a lunar month being 29 ½ days long, and not coinciding perfectly with calendar months that can be 28, 29, 30, or 31 days long.

The second calendar-month full moon is called a blue moon. Because January’s blue moon comes on the last day of the month, the short month February will have no full moon at all, while March will have another blue moon!

The reason for the name blue moon is obscure, but in January we can nearly guarantee that its actual color will be red, not blue. This is thanks to the fact that the moon will pass through the shadow of the Earth, resulting in a total lunar eclipse.

From Los Angeles, the eclipse starts on January 31 at 2:51 a.m. and ends, with the moon still partially immersed in Earth’s shadow, when it sets at 6:56 a.m. The outer shadow of the Earth, called the penumbra, has a very indistinct outer boundary, and as a result, it does not have any visible effect on the full moon until the moon is about halfway covered by it, which will happen at about 3:20 a.m.

At that time, the lower left edge of the moon will start to fade, and at 3:48 a.m., a sharp bite will appear to be missing from that edge, caused by the dark inner shadow of the Earth, the umbra.

The moon will take about an hour to slip completely into the umbra, which it will at 4:51 a.m., and the eclipse will be total. Instead of the bright white full moon, only red rays of sunlight bent into Earth’s shadow by its atmosphere, illuminate it with a coppery-red glow produced by all of the sunsets and sunrises happening on Earth. Dawn will begin at the mid-point of the eclipse, at 5:31 a.m., and the moon will begin to emerge from the umbra at 6:07 a.m.

The first full moon of the month, on New Years Day, will also happen at about the same time that it is closest to the earth. Every month, the moon orbits the earth, at an average distance of 239,000 miles. Its orbit is elliptical, and comes as close as 231,000 miles, the moon’s perigee (close point to Earth), and moves out to its farthest point (apogee) about two weeks later, when it is 252,000 miles away. Although the effect of the full moon happening at perigee is subtle, it is has become popular to celebrate the coincidence as a “supermoon.”

The earth also travels in an elliptical orbit, and over the year its distance ranges from 91.4 million miles when it is closest to the sun (perihelion) to as far as 94.5 million miles (aphelion). Perihelion happens in early January, and aphelion is in early July. This year, perihelion occurs on January 2 at 9:36 p.m., PST.

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