Lunar Facts

The word month is derived from the word "moonth" which was used to describe the period of time from new moon to new moon.

February is the only month of the year which can have no full moon. The last such February was in 1866.

The surface of the Moon has about the same area as the continent of Africa.

The largest named crater on the visible side of the Moon is Bailly, a huge walled plain near the southern limb of the Moon. It is 183 miles (294 km) in diameter and its walls rise up to 14,000 feet in many places. At top speed, it would take the lunar Rover about a week to travel around Bailly's circumference.

The crater called Copernicus is considered to be the most impressive crater on the Moon. Copernicus has a diameter of 56 miles (91 km.) The crater's massive walls reach heights of 17,000 feet (5.183 meters) which is twice as high as the Grand Canyon of Earth!

The old, or waning crescent moon shows light on the left side, and is seen in the eastern sky before sunrise.

The new, or waxing crescent moon shows light on the right side, and is seen in the western sky after sunset.

During one lunar month, the phases progress in sequence, with the area of light or shadow always moving from the right to the left in the northern hemisphere.

When the Moon is waning, the line separating light from dark is called the evening, or sunset terminator.

When the Moon is waxing, the line separating light from dark is called the sunrise, or morning terminator.

Moonrise or moonset is defined as the instant when the upper limb of the Moon is even with the horizon.

The exact time of moonrise is affected by the observer's latitude and longitude.

To find moon phases, or your local time of moonrise and moonset as well as eclipse information, visit the Naval Observatory on the web at http://riemann.usno.navy.mil/AA/data/

The first and last quarter moon are only about 9 percent as bright as the full moon.

When the first crescent moon is only a few days old, light reflected back from Earth (earthshine) will sometimes illuminate the whole lunar surface.

When the new crescent moon is less than 24 hours old, it is still very close to the Sun and extremely difficult to see because the sky is too light for contrast.

The earliest the first crescent Moon has been sighted with the naked eye is 15 hours, 30 minutes.

The earliest the first crescent Moon has been sighted with binoculars is 13 hours, 32 minutes.

The earliest the first crescent Moon has been sighted with a telescope is 12 hours, 7 minutes.

For each additional calendar day after the new moon, the young crescent moon appears another 13 degrees further up in the sky.

The Moon appears to tilt as it rises, moves across the sky and sets. This visual effect is caused by the curved path the Moon takes across he sky. Most images of the Moon represent its position at the top of this curved path, the zenith.

A lunar halo, also called a "ring around the Moon," is caused by light refracted through ice crystals in cirrus clouds. These six sided ice crystals refract the light at a 22 degree angle, almost always producing a halo that is 22 degrees in diameter.

A lunar halo very often precedes precipitation by about 24 hours.

The Moon's orbit around the Earth is a slightly squashed circle called an ellipse.

During a full or new moon, the elliptical shape of the Moon's orbit can be changed slightly if the phase occurs when the Moon is already at it's closest or furthest distance from Earth.

The Moon travels at different speeds during different parts of its orbit. It moves slowest when it is at furthest distance from Earth. The Moon moves fastest in its orbit when it is closest to Earth.

The apparent motion of the Moon across the sky is mostly caused by the rotation of the Earth. The speed of the Earth's rotation accounts for about 96 percent of the Moon's visible motion. Only 4 percent is from the Moon's actual movement in orbit.

The gravitational attraction of the Moon is only one ten-millionth of the gravitational force of the Earth itself, but combined with other forces - including the centripetal force created by the spin of the Earth - it is one factor that produces tides on the Earth's oceans.

The Moon also causes tides in the Earth's atmosphere, but they are only a fraction of ocean tides.

During full and new moons the gravitational forces of the Sun and Moon combine to produce the highest tides called Spring Tides.

During quarter moons the gravitational forces of the Sun and the Moon oppose each other to produce the lowest tides called Neap Tides.

Tractive forces are created by the pull of the Moon's gravity around the sides of the Earth, building up to a tidal bulge under the highest point in the Moon's path.

To an observer on Earth, the Moon takes about two minutes to move its own diameter to the west.

From one night to the next (at the same local time,) the Moon "lags behind" about 13 degrees to the east.

Two bodies rotating around each other such as the Earth and Moon have a common center of mass known as the barycenter. The barycenter of the Earth and Moon is about 3,000 miles out from the center of the Earth, or about 900 miles under your feet! The actual location changes slightly because the distance between the Earth and Moon varies during the Moon's monthly orbit.

Footprints left on the Moon by Apollo astronauts will remain visible for at least 10 million years because there is no erosion on the Moon.

Life could survive on the Moon. The Apollo 12 astronauts, Conrad, Gordon and Bean, brought back life from the Moon: a terrestrial bacterium found on a piece of foam inside the camera of the Surveyor 3 lander. The bacterium survived for 2 and a half years on the lunar surface!

Constellations

The Solar System