Half-lit first quarter moon on January 16

Click here to see animation. As seen from the north side of the moon’s orbital plane, the Earth rotates counterclockwise on its rotational axis, and the moon revolves counterclockwise around Earth. The terminators of the Earth and moon align at first and last quarter moon.

The moon reaches its half-illuminated first quarter phase on January 16, at 23:26 Universal Time. Although this first quarter moon happens at the same instant worldwide, it occurs at different times by the clock, depending on one’s time zone. Here, in the mainland United States, the first quarter moon comes on January 16 at 6:26 p.m. EST, 5:26 p.m. CST, 4:26 p.m. MST and 3:26 p.m. PST.

At first quarter phase, one half of the lunar disk is illuminated by sunlight and the nighttime half is submerged in the moon’s own shadow. The lunar terminator – the shadow line dividing day from night – shows you where it’s sunrise on the first quarter moon as it waxes toward full moon. It’s along the terminator that you have your best three-dimensional views of the lunar terrain through binoculars or the telescope.

If you were on the moon at its first quarter phase, and looking back at Earth, you’d see the Earth at its last quarter phase, as displayed on the image below. As seen from the moon, the terminator on the last quarter Earth depicts sunset, as the last quarter Earth wanes toward its new phase.

Simulation of the last quarter Earth as viewed from the first quarter moon (2016 January 16 at 23:26 Universal Time). As seen from the moon, the Earth’s terminator represents sunset, and the Earth is waning toward new phase. Image credit: Earth and Moon Viewer

However, when the last quarter moon comes on February 1, the lunar terminator will show you where it’s sunset on the last quarter moon. Yet, from the vantage point of last quarter moon, the earthly terminator would show you where it’s sunrise on the first quarter Earth.

Simulation of the first quarter Earth as viewed from the last quarter moon (2016 February 1 at 3:28 Universal Time). As seen from the moon, the Earth’s terminator represents sunrise and the Earth is waxing toward full phase. Image credit: Earth and Moon Viewer

After today’s first quarter moon, the moon will wax toward full moon. But, as seen from the moon, today’s last quarter Earth will wane toward Earth at its new phase.

Approximately one week after today’s first quarter moon, it’ll be a full moon in Earth’s sky but a new Earth in the moon’s sky.

Enjoy tonight’s first quarter moon!

from EarthSky http://ift.tt/1OJbK6c