June 4th Lunar Eclipse

With all the excitement over the upcoming Venus transit, the upcoming partial lunar eclipse has been getting short shrift. Tomorrow morning, June 4th for the U.S., the Moon will be partially covered by the Earth’s shadow. This eclipse occurs in the early morning. The penumbral portion of the eclipse begins at 8:48UT (1:48am PDT). The penumbral eclipse occurs when the Moon enters the outer portion of Earth’s shadow. It is difficult to tell much change at this point. A deep penumbral eclipse can be seen by careful observers (the Moon will dim and the quality of the light will change). You will really notice when the umbral phase begins at 9:59 UT (2:59am PDT). That’s when the Moon enters the umbra (dark portion) of Earth’s shadow and you start seeing a “bite” taken out of the Moon. Maximum eclipse occurs at 11:04UT (4:04am PDT) when about 37% of the Sun will be covered. Umbral phase ends at 12:06UT (5:06am PDT) which is just a few minutes before sunrise in Tucson. The penumbral phase ends after sunrise for the U.S. at 13:18UT (6:18 PDT). Here is a NASA graphic showing the times and path of the Moon through Earth’s shadow. Check out NASA’s page on the eclipse as well.

You might have noticed that this comes about two weeks after our annular eclipse. This is not an accident. The Moon’s orbit is tilted about five degrees with respect to the Earth-Sun plane. There are two points at which the Earth-Moon-Sun line up: one when the Moon is closer to the Sun and one when it is farther from the Sun. On May 20th, the Moon was at the point between the Earth and the Sun where it lined up. Two weeks later, the Moon is on the opposite side of the Earth where they all line up.  So usually when you get a solar (or lunar) eclipse, you get the other type about two weeks later. Of course, you may be on the wrong side of the planet to see one or even both of them,but someone gets to see them!

So be sure to check out the Moon tomorrow if you hare an early riser.