Photo by NASA
Tonight a full moon will again occupy the night sky. From Earth, we see the full Sun-lighted half of the moon, while its dark side faces away from us. This happens when the moon is opposite the Sun in its orbit around Earth.
In two weeks, at the new moon, the three celestial bodies will line up precisely—Earth, moon, and Sun—and we’ll experience a total solar eclipse. But tonight is another particular alignment, a nearly straight line of moon, Earth, and Sun.
When celestial bodies line up, the conditions are set for eclipses (and transits) to happen. Tonight, if you live in parts of Asia, Europe, Africa, or Australia, you can observe a partial lunar eclipse. The Earth, moving between the other two, will cast its shadow onto part of the moon.
Such a convergence of eclipses may seem remarkable, but in fact it’s the same orbital conditions that cause both the solar and lunar versions. The two occur in tandem, with solar eclipses always preceded or followed (sometimes both) by a lunar eclipse at the closest full moon. You won’t always see them from your location, but they’re happening somewhere.
We’re now just half a moon cycle from the total solar eclipse, which will happen at the next new moon. This series has taken you through a full orbit and all of the moon’s phases. From here, you can follow the moon as it wanes to a quarter and then a crescent, anticipating the moment on August 21 when it blocks the Sun from view. Happy moon-watching!
(for all posts in our Moon to the Eclipse series)
The moon orbits the Earth about once a month. As it circles our planet, we see different amounts of the lighted and dark sides of the moon. The blue boxes mark tonight's moon.
Orbit illustration by Karl Tate, SPACE.com, from NASA. Moon phase photos by Fred Espenak.