Last Monday, the western United States had the chance to see the Moon pass between Venus and Earth. Even though it occurred during the day, this special event was still visible to the naked eye since Venus is so bright. Luckily, we were ready to witness and document this rather rare phenomenon. The Los Alamos Nature Center patio was occupied by excited sky watchers of all ages. We set up a telescope and used binoculars to get a better view of Venus’ reappearance.
Before dawn on Monday, the crescent Moon and Venus were close together. As the morning progressed, it quickly became clear that the Moon would pass in front of Venus. After sunrise, when the moon was very close to Venus, observers could easily see this neighboring planet with the naked eye!
The thin crescent of the Moon officially occulted, blocked, Venus at about 9:30 a.m. Since Los Alamos was on the center line of this occultation, Venus was out of sight for over an hour and a half. Then, as if by magic, Venus reappeared at 11:19 a.m. Again, since we knew exactly where to look, we could see it in broad daylight.
More on Occultations
It is rather rare for the Moon to occult our line of sight of the planets. Even though the Moon is much smaller than our neighboring planets, it appears significantly larger in the sky. This is due to it’s relative distance to Earth. Objects closer to Earth will appear larger than objects farther away.
Occultations also help astronomers determine relative distance to Earth, because the object that disappears must be farther away from us than the object that remains in our sight. Thus, Monday’s occultation confirms that the Moon is closer to Earth than Venus.
Venus was blocked from view for one hour and forty-nine minutes. However, it takes the Moon about one hour to travel the distance of its diameter. So why did it take so much longer? The answer lies in the Earth’s rotation. The Moon orbits Earth in the same direction as Earth’s rotation. During the occultation, the Earth’s rotation kept the Moon in line with Venus and our location on Earth longer than the time it takes the Moon to travel the distance of its diameter.
Here is your chance to be an astronomer. The photo above was taken just as Venus reappeared. Can you explain why Venus emerged so far away from the Moon’s crescent?
Keep Looking Up
I noticed this occultation by watching the sky. I had not seen a prediction or notification. So keep looking up. You never know what you’ll see.
Article by Chick Keller. Photo by Craig Martin