Moon Question of the Day

How come longitude lines start in Greenwich, England?

The Royal Observatory Greenwich is located at the National Maritime Museum in London. The original site of the observatory was arbitrarily chosen as longitude 0 degrees in 1884. A plaque in the original structure marks the zero point from which longitude is calculated. The observatory was founded in 1675 by King Charles II to keep accurate tables of the position of the Moon for the calculation of longitude by English ships. In 1750 those tables were published as the Astronomical Observations, and after 1838 they were published annually. Meridian observations of the Sun, stars, and planets also were made at the observatory. Photographs of the Sun were taken daily, conditions permitting, and a continuous photographic record of sunspots was kept starting in 1873. Today the observatory is primarily a museum with a small planetarium.

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Last 7 Days

What causes the distance from Earth to the Moon to vary?

The celestial mechanics of the Moon's motion are very complex. When the distance to the Moon is measured at different times of the month, it is found to vary by more than 10 percent because the Moon's orbit is basically an ellipse, with Earth at one focus. The Moon may come as close as 356,334 kilometers (220,927 miles) to Earth's center and then move as far away from it as 406,610 kilometers (252,098 miles). The dates when the Moon is at apogee (the point in its orbit farthest from Earth) and perigee (the point in its orbit closest to Earth) can be found on each month's calendar page in The Old Farmer's Almanac. However, to understand the "mechanics," as mentioned above, we recommend consulting a basic astronomy textbook.

Is it true that the weather changes (good to bad, bad to good) at the full Moon?

Weather records confirm that the days following both the new and full Moons are most likely to be rainy or stormy. A winter full Moon is a time for long cold snaps. In April, the full Moon brings frost. Sailors agree that the full Moon "eats clouds." Two full Moons in a month increase the chances of flood. A pale full Moon indicates rain, and a red one brings wind. A Christmas full Moon predicts a poor harvest.

Does the Moon rise and set as the Sun rises in the east and sets in the west? The enormous full Moon always takes me by surprise, and I'd love to get some shots of a big yellow Moon. Is it possible to predict the dates and times when the Moon will appear largest over the horizon?

Basically, the Moon rises in the east and sets in the west, but its path varies during the month because its orbit is elliptical. However, you will never see a rising Moon in the west or a setting Moon in the east. The time to see a huge Moon is in its full phase and when it is close to the horizon. If you check the right-hand calendar pages in the print Almanac, you will see the notation "Moon runs low"; this is when it is closest to the horizon. Check the date for each such notation, then check the left-hand calendar page for the Moon's phase and the time of its rising and setting for that date.

What is the temperature on the Moon?

Daytime temperature is about 235 degrees F. Nighttime temperatures can drop to -275 degrees F.

When does a new Moon rise?

The new Moon always rises at sunrise. The full Moon always rises at sunset.

Is the temperature colder during a full Moon?

Air temperature is not affected by Moon phase. It is affected by the season and whether there is a cloud cover, among other things. On a clear night, heat rises from Earth if there is no cloud cover holding it in. This might make you think it's colder because there is a full Moon, but it's really colder just because the sky is clear.

Who were the Roman and Greek goddesses of the Moon and the sea?

Diana was the Roman goddess of the Moon. She was a "multipurpose" goddess, presiding over the hunt and childbirth, among other things. In her incarnation as Moon goddess, she was known as Luna. Artemis was the Greek goddess of the Moon. Gods, not goddesses, ruled the sea -- Neptune in Roman mythology and Poseidon in Greek.

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