Moon Question of the Day

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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.

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Last 7 Days

When does a new Moon rise?

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

What does neaped mean in reference to a ship?

A boat that is neaped has gone aground on a mild tide and needs a spring tide or stormy waters to float it off. The boat is only barely aground, as opposed to being hard aground, where even a very high tide or rough waters might not be enough to set it free. The expression comes from the term "neap tide," which is a moderate tide. Neap tides occur when Earth, Moon, and Sun are in quadrature. In other words, instead of being lined up in a straight line, as at syzygy, they are more nearly at right angles. True quadrature happens at regular intervals, about twice a month, at the first quarter and last quarter Moons, but neap tides occur for several days around those dates. Take a look at the tides on the right-hand calendar pages of The Old Farmer's Almanac, and you'll notice that high tides are considerably higher around the full Moon and new Moon than around the first and last quarters.

Has anyone else seen a Moon rainbow? If so, are they common?

The lunary rainbow, seldom seen, is usually observable soon after dark, following a brief summer storm or shower, when the Moon is nearly full.

How much would you weigh on the Moon?

Just multiply your weight (it doesn't matter if it's in pounds or kilograms) by 0.165. You'd weigh about 80 percent less!

Are there any ancient cultures known to have had a Copernican model of the solar system?

We can't find any record of a culture that believed the Sun was the center of the universe, but Copernicus wasn't the first person to say this. Around 270 B.C., on Samos (an island off the coast of what is now Turkey), Aristarchus put forth a theory of a sun-centered universe, which included his belief that the Moon's light came from the Sun. He is sometimes referred to as the Copernicus of antiquity.

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.

I was told about a documented case in which onlookers saw a blood-red Moon and stars falling from the sky. Where might I find this piece of documentation?

Astronomically speaking, it is possible to observe a "bloody" Moon during a lunar eclipse, when Earth's shadow casts a dark reddish color on the Moon. And, indeed, stars often appear to "fall" from the sky. But we think that what you have in mind is not an astronomically documented case but a quote from the Bible, specifically from Revelation (6:12-13): "And the sun became black as sackcloth of hair, and the moon became as blood; And the stars of heaven fell unto the earth, even as a fig tree casteth her untimely figs, when she is shaken of a mighty wind."

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