New Moon This is the first of the moon phases On the day of new moon, the moon rises when the sun rises. It sets when the sun sets. It crosses the sky with the sun during the day. That’s why we can’t see the new moon in the sky. It is too close to the sun’s glare to be visible. Plus its lighted hemisphere is facing away from us.

Then a day or two later, the moon reappears, in the west after sunset. Then it’s a slim waxing crescent visible only briefly after sunset – what some call a young moon.

Each new lunar cycle is measured beginning at each new moon. Astronomers call one lunar cycle a lunation.

Waxing Crescent Moon"Waxing" means growing and refers to the size of the illuminated part of the moon that is increasing. At this moon phase, the Earth, moon and sun are located nearly on a line in space. If they were more precisely on a line, as they are at new moon, we wouldn’t see the moon. The moon would travel across the sky during the day, lost in the sun’s glare, but a waxing crescent moon is far enough away from that Earth-sun line to be visible near the sun’s glare – that is, in the west after sunset. This moon phase is seen one day to several days after new moon. On these days, the moon rises one hour to several hours behind the sun and follows the sun across the sky during the day. When the sun sets, and the sky darkens, the moon pops into view in the western sky.

First Quarter Moon The first quarter Moon rises at noon. But we officially call this moon a quarter and not a half because it is one quarter of the way around in its orbit of Earth, as measured from one new moon to the next. This moon appears half-lit to us, and half moon is a beloved name (although not an official one). Still, it’s good to recall that the illuminated portion of a first quarter moon truly is just a quarter. On the night of first quarter moon, we see half the moon’s day side, or a true quarter of the moon. Another lighted quarter of the moon shines just as brightly in the direction opposite Earth!

A first quarter moon rises at noon and is high overhead at sunset. It sets around midnight.

First quarter moon comes a week after new moon. Now, as seen from above, the moon in its orbit around Earth is at right angles to a line between the Earth and sun.

Waxing Gibbous Moon

A waxing gibbous moon appears high in the east at sunset. It’s more than half-lighted, but less than full.

This moon phase comes between one and two weeks after new moon.

The moon has moved in its orbit so that it’s now relatively far from the sun in our sky. A waxing gibbous moon rises during the hours between noon and sunset. It sets in the wee hours after midnight.

People sometimes see a waxing gibbous moon in the afternoon, shortly after moonrise, while it’s ascending in the east as the sun is descending in the west. It’s easy to see a waxing gibbous moon in the daytime because, at this phase of the moon, a large fraction of the moon’s day side is facing our way. Thus a waxing gibbous moon is more noticeable in the sky than a crescent moon, with only a slim fraction of the lunar day side visible. Also, a waxing gibbous moon is far from the sun on the sky’s dome, so the sun’s glare isn’t hiding it from view.

Any moon that appears more than half lighted but less than full is called a gibbous moon. The word gibbous comes from a root word that means hump-backed. You can see the hump-backed shape of the waxing gibbous moon.

Full Moon The full moon occurs when the Moon lies on the opposite side of Earth from the Sun. The moon as seen from the surface of the earth is fully illuminated by the sun at this time, presenting a "full" round disc to viewers on earth. As always, only half the total surface of the moon is illuminated. The full moon reaches its highest elevation at midnight

A full moon is the only time when a lunar eclipse is possible; at that time the moon may move through the shadow cast by the earth. However, because of the tilt of the moon's orbit around the earth relative to the earth's orbit around the sun, the moon may pass above or below the shadow, so a lunar eclipse does not occur at every full moon. Full moons are generally a poor time to conduct astronomical observations, since the bright reflected sunlight from the moon overwhelms the dimmer light from stars.

Waning Gibbous Moon"Waning" means shrinking.When the the Moon is said to be waning, we see a little less of the Moon each day until it completely disappears when the Moon is New.

Last Quarter Moon The last quarter Moon rises at midnight Last quarter moon comes about three weeks after new moon. Now, as seen from above, the moon in its orbit around Earth is at right angles to a line between the Earth and sun. The moon is now three- quarters of the way around in its orbit of Earth, as measured from one new moon to the next.

It’s very cool to see the last quarter moon just after it rises, around midnight. The image at the top of this post illustrates it well. Just after the last quarter moon rises, its lighted portion is always facing downwards, more or less toward the horizon. Why? Because you’re on the midnight portion of Earth – with the sun below your feet – just as it’s below this moon.

After the last quarter phase, the moon will begin edging noticeably closer to the sun again on the sky’s dome. Fewer people notice the moon during the day from about last quarter on, because the sun’s glare begins to dominate the moon.

A last quarter moon can be used as a guidepost to Earth’s direction of motion in orbit around the sun. In other words, when you look at a last quarter moon high in the predawn sky, you’re gazing out approximately along the path of Earth’s orbit, in a forward direction. The moon is moving in orbit around the sun with the Earth. But, if we could somehow anchor the moon in space . . . tie it down, keep it still . . . Earth’s orbital speed of 18 miles per second would carry us across the space between us and the moon in only a few hours.

Waning Crescent Moon

A waning crescent moon is sometimes called an old moon. It’s seen in the east before dawn.

Now the moon has moved nearly entirely around in its orbit of Earth, as measured from one new moon to the next.

Photo Credit: Brunk Ford Braun Because the moon is nearly on a line with the Earth and sun again, the day hemisphere of the moon is facing mostly away from us once more. We see only a slender fraction of the moon’s day side: a crescent moon.

Each morning before dawn, because the moon is moving eastward in orbit around Earth, the moon appears closer to the sunrise glare. We see less and less of the moon’s day side, and thus the crescent in the east before dawn appears thinner each day.

The moon, as always, is rising in the east day after day. But most people won’t see this moon phase unless they get up early. When the sun comes up, and the sky grows brighter, the waning crescent moon fades. Now the moon is so near the Earth/sun line that the sun’s glare is drowning this slim moon from view.

Still, the waning crescent is up there, nearly all day long, moving ahead of the sun across the sky’s dome. It sets in the west several hours or less before sunset.