How often does the crescent moon appear at the bottom?

[mbthomps57]

I am wondering how often in a year the cycle following the new moon has the crescent appearing at the bottom like it did on Feb. 11-15, 2013?

[Chris Peterson]

I am wondering how often in a year the cycle following the new moon has the crescent appearing at the bottom like it did on Feb. 11-15, 2013?

Not sure exactly what you're asking. A crescent Moon always has the crescent pointing towards the Sun. A thin crescent Moon is fairly close to the Sun, so if you view it when the Sun is below the horizon, it will always be pointing towards the horizon ("down"). The ecliptic is steeper near the equinoxes, so around those times the crescent is particularly parallel to the horizon.

[THX1138]

With my 10” reflector the smaller the sliver of the moon is the better, I can see the mountains, valleys and the craters crystal clearly. Looking at the full moon is not even close to as cool to look at and if you do so for more than a few minutes you will get a headache. Even with a moon filter nothing beats the view when its just a small sliver. Is there anything I can do with my optics to change this situation

[rstevenson]

With my 10” reflector the smaller the sliver of the moon is the better, I can see the mountains, valleys and the craters crystal clearly. Looking at the full moon is not even close to as cool to look at and if you do so for more than a few minutes you will get a headache. Even with a moon filter nothing beats the view when its just a small sliver. Is there anything I can do with my optics to change this situation

So you basically want to tone down the brightness and increase the contrast when the Moon is closer to full? Back in the day, when I had lots of non-digital photography stuff around, I used a polarizing filter for such things. I've no idea if such a filter can be had for a telescope, nor whether it would be useful. But you might check one out if a fellow telescopist has one you can borrow.

Of course, the main reason why you see the landscape more dramatically when the Moon is a thin crescent is that the longer shadows make the depth of the terrain easier to see.

Rob

[Chris Peterson]

With my 10” reflector the smaller the sliver of the moon is the better, I can see the mountains, valleys and the craters crystal clearly. Looking at the full moon is not even close to as cool to look at and if you do so for more than a few minutes you will get a headache. Even with a moon filter nothing beats the view when its just a small sliver. Is there anything I can do with my optics to change this situation

When the Moon is near full, there are no shadows being cast, so it's difficult to see much structure. At all times, visual observation of the Moon is best along the terminator, where the shadows are longest. Nothing you can really do except plan your observing around the lunar phases.

With imaging, you have somewhat more flexibility, since you can stretch the contrast of an image to bring out detail. No way to do that with your eyes, though. (I've been designing a technique involving some clever electronics and implanted brain electrodes, but I need a volunteer. Interested?)

[Chris Peterson]

So you basically want to tone down the brightness and increase the contrast when the Moon is closer to full? Back in the day, when I had lots of non-digital photography stuff around, I used a polarizing filter for such things. I've no idea if such a filter can be had for a telescope, nor whether it would be useful.

The light coming from the Moon isn't polarized, so a single filter isn't useful (except it does increase the contrast against the sky during daytime viewing or imaging). You can buy a crossed polarizer for telescope eyepieces that allows you to selectively attenuate the light. However, the Moon isn't really as bright as it seems, and most serious lunar observers have found that any attempt to filter the brightness also results in less detail. Our eyes work best with bright light. The Moon is already pretty dark- the impression of it being blindingly bright through a telescope is one of dazzle when we are already partly dark adapted, and also the imbalance of having a bright source in one eye and not the other. Switching between eyes can help, having some local light (as from a lantern) can help, and using a binocular eyepiece system really makes viewing the Moon pleasant.

[rstevenson]

You can buy a crossed polarizer for telescope eyepieces that allows you to selectively attenuate the light.

Ah yes, that's what I used back then, a crossed polarizer. Turn the ring to increase the effect. Now that the memory cells are stimulated, I recall that this mostly conteracted the contrast-reducing effect of atmospheric haze. (If it need be said, I never tried photographing anything astronomical back then.)

Rob

[neufer]

I am wondering how often in a year the cycle following the new moon has the crescent appearing at the bottom like it did on Feb. 11-15, 2013?

Not sure exactly what you're asking. A crescent Moon always has the crescent pointing towards the Sun. A thin crescent Moon is fairly close to the Sun, so if you view it when the Sun is below the horizon, it will always be pointing towards the horizon ("down"). The ecliptic is steeper near the equinoxes, so around those times the crescent is particularly parallel to the horizon.

[b][color=#0000FF]Path of a dry (wet Hawaiian Summer/September) moon (left) and a wet (dry Hawaiian Winter/March) moon (right).[/color][/b]

---

<<A wet moon (also called a Cheshire moon) is a lunar phase when the "horns" of the crescent moon point up at an angle, away from the horizon, so the moon's crescent takes on the appearance of a bowl or a smile. A wet moon occurs when the crescent moon is near the horizon at a point more or less directly above the sun's (invisible) position below the horizon. This in turn is determined by the earth's and moon's positions in their orbits, the inclination of these orbits relative one another and to the earth's axis, and observer's latitude on the earth. Wet moons occur routinely in the tropics (where the sun and moon rise and set nearly vertically), and rarely in polar regions (where the sun and moon rise and set at a glancing angle or not at all).

The terms wet moon and dry moon originate from Hawaiian mythology, where it was thought that the moon appeared as a bowl which would fill up with rain. As the year passes into summer, the crescent shape shifts, pouring out the water and causing the summer rains/hurricanes. After the "bowl" empties, it dries out and rights itself, creating the "dry moon".

The term "Cheshire moon" is a reference to the smile of the Cheshire Cat of Lewis Carroll's story Alice's Adventures in Wonderland.>>

[oneironman]

Should be once a month.

[Chris Peterson]

Should be once a month.

Twice, considering that both the old and new moons show as crescents just above the horizon. However, since the angle that the Moon's path makes relative to the horizon changes, not all crescent moons will appear parallel to the horizon. While they will always point generally down (that is, with their horns up), there can be quite a lot of tilt.