FULL MOON and her phases, a wondrous natural sight

The July 2012 full moon falls on Tuesday, July 3, at 18:52 Universal Time. Although the full moon comes at the same instant for everyone worldwide, the clock – as always – reads differently according to time zone. In the United States, the full moon occurs on July 3 at 2:52 p.m. Eastern Daylight Time, 1:52 p.m. Central Daylight Time, 12:52 p.m. Mountain Daylight Time and 11:52 a.m. Pacific Daylight Time.

For us across the United States, the moon turns astronomically full – or stands most directly opposite the sun – during the daylight hours today. But for general reference, we can say the moon is full all night tonight for us and the rest of the world.

At full moon, we are seeing all of the moon’s day side.

The moon and sun are on a line, with Earth in between. It’s as though Earth is the fulcrum of a seesaw, and the moon and sun are sitting on either end of the seesaw. Thus as the sun sets in the west, the full moon rises. When the sun is below our feet at midnight, the full moon is highest in the sky. When the sun rises again at dawn, the full moon is setting.

 

Each full moon has its own name, here are the names by month:

January: Old Moon, or Moon After Yule
February: Snow Moon, Hunger Moon, or Wolf Moon
March: Sap Moon, Crow Moon, or Lenten Moon
April: Grass Moon, or Egg Moon
May: Planting Moon, or Milk Moon
June: Rose Moon, Flower Moon, or Strawberry Moon
July: Thunder Moon, or Hay Moon
August: Green Corn Moon, or Grain Moon
September: Fruit Moon, or Harvest Moon
October: Harvest Moon, or Hunter’s Moon
November: Hunter’s Moon, Frosty Moon, or Beaver Moon
December: Moon Before Yule, or Long Night Moon

In many ways, a full moon is the opposite of a new moon. At both the new and full phases, the moon is on a line with the Earth and sun. At new moon, the moon is in the middle position along the line. At full moon, Earth is in the middle.

Full moon always comes about two weeks after new moon, when the moon is midway around in its orbit of Earth, as measured from one new moon to the next.

If there is a lunar eclipse, it must happen at full moon. It’s only at the full moon phase that Earth’s shadow, extending opposite the sun, can fall on the moon’s face.

As the moon orbits Earth, it changes phase in an orderly way.

The following will help you to understand the various phases of the moon.

Understanding Moon Phases

Waxing Crescent
A waxing crescent moon – sometimes called a young moon – is always seen in the west after sunset. 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
A first quarter moon shows half of its lighted hemisphere – half of its day side – to Earth. 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!

Waxing Gibbous
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.

Full Moon
At full moon, we are seeing all of the moon’s day side. The moon and sun are on a line, with Earth in between. It’s as though Earth is the fulcrum of a seesaw, and the moon and sun are sitting on either end of the seesaw. Thus as the sun sets in the west, the full moon rises. When the sun is below our feet at midnight, the full moon is highest in the sky. When the sun rises again at dawn, the full moon is setting.

In many ways, a full moon is the opposite of a new moon. At both the new and full phases, the moon is on a line with the Earth and sun. At new moon, the moon is in the middle position along the line. At full moon, Earth is in the middle.

Full moon always comes about two weeks after new moon, when the moon is midway around in its orbit of Earth, as measured from one new moon to the next.

If there is a lunar eclipse, it must happen at full moon. It’s only at the full moon phase that Earth’s shadow, extending opposite the sun, can fall on the moon’s face.

Waning Gibbous
A waning gibbous moon sails over the eastern horizon in the hours between sunset and midnight. The moon is past full now. Once again, it appears less than full but more than half lighted.What can I say about a waning gibbous moon? Only that it can surprise you if you happen to be out late in the evening. It rises eerily some hours after sunset, glowing red like a full moon when it’s near the horizon. Sometimes it looks like a misshapen clone of a full moon. Because it comes up late at night, the waning gibbous moon prompts people to start asking, “Where is the moon? I looked for it last night and couldn’t find it.”

The waning gibbous moon also initiates a rash of questions about seeing the moon during the day. If it rises late at night, you know the waning gibbous moon must set after sunrise. In fact, in the few days after full moon, you’ll often see the waning gibbous moon in the west in early morning, floating against the pale blue sky.

Last Quarter
A last quarter moon looks half-illuminated. It rises around midnight, appears at its highest in the sky at dawn, and sets around noon. 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.

After this, 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
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. 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.

New Moon
What is the ghostly image at the top of this post? It’s a new moon. Its lighted half is facing entirely away from Earth. The image above is imaginary. It’s as if you flew in a spaceship to a place where you could see the night side of the moon. Why do we say imaginary?

Because, when the moon is new, its night face is facing us on Earth … and we can’t see the moon at this time. We can’t see the new moon from Earth, except during the stirring moments of a solar eclipse. Then the moon passes in front of the sun, and the night portion of the moon becomes visible to us, surrounded by the sun’s fiery corona.

The next FULL MOON will be seen on AUGUST 1, 2012

MOON PHASES

Information thanks to EarthSky.org