Moon Question of the Day

What exactly is a waning or waxing gibbous or crescent Moon?

First, gibbous refers to the shape you can see when the lighted surface of the Moon is bigger than a crescent shape; the crescent shape is defined by the distinct points on the lighted sliver. The Moon moves in these phases: new Moon, waxing crescent, first quarter Moon, waxing gibbous, full Moon, waning gibbous, last quarter Moon, waning crescent, back to new Moon. So waxing means the moon is on its way to being full; waning means the Moon is on its way to being new (the phase you really can't see).

Last 7 Days

    What exactly is a waning or waxing gibbous or crescent Moon?

    First, gibbous refers to the shape you can see when the lighted surface of the Moon is bigger than a crescent shape; the crescent shape is defined by the distinct points on the lighted sliver. The Moon moves in these phases: new Moon, waxing crescent, first quarter Moon, waxing gibbous, full Moon, waning gibbous, last quarter Moon, waning crescent, back to new Moon. So waxing means the moon is on its way to being full; waning means the Moon is on its way to being new (the phase you really can't see).

    Why do stars twinkle, while the visible planets (and our Moon) shine constantly when viewed?

    First, the stars themselves do not twinkle. We are seeing the effect of Earth's atmosphere on the light they produce. The starlight is bent by moving volumes of air in our atmosphere. The bending effect makes the stars appear to be larger than points, to dance around slightly, and to change in intensity, which is what is commonly called twinkling. Planets don't usually appear to twinkle because they are close enough to Earth that they appear as tiny disks of light. The total intensity doesn't seem to change -- hence no twinkling is apparent to the naked eye.

    Why do stars twinkle, while the visible planets (and our Moon) shine constantly when viewed?

    First, the stars themselves do not twinkle. We are seeing the effect of Earth's atmosphere on the light they produce. The starlight is bent by moving volumes of air in our atmosphere. The bending effect makes the stars appear to be larger than points, to dance around slightly, and to change in intensity, which is what is commonly called twinkling. Planets don't usually appear to twinkle because they are close enough to Earth that they appear as tiny disks of light. The total intensity doesn't seem to change -- hence no twinkling is apparent to the naked eye.

    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.

    Can you please tell me where I should go to see the "horns" of the Moon pointing up?

    Around 18 to 28 degrees north latitude, the horns of the Moon at times point directly up. This happens just after sunset in the west, near the horizon, for a waxing Moon and just before sunrise in the east, near the horizon, for a waning moon. The same is true at around 18 to 28 degrees south latitude--just exchange east and west. A beautiful picture of the Moon with its horns pointing upward (but not straight up) is visible over a much wider area. In the United States, southern Florida is a great place to see this.

    What would happen if Earth's rotation started to slow down?

    Earth is already slowing down and has been doing so for billions of years. At the present time, our planet is slowing down by about .002 second per century. The slowing occurs mainly because of friction between solid earth and ocean tides. Earth's loss of rotational energy is transferred to the Moon, which goes into a wider orbit, thus lengthening the time between successive full Moons.

    What is the most recent year that had a full Moon on February 29?

    This occurred most recently in 1972. This is indeed a rare event, since the next most recent year was 1820.

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