Moon questions

When I was a stargazing youngster, I remember some source or other telling me that such-and-such phase was the best time to view such-and-such feature of the moon’s surface. E.g., “gibbous waxing is the best time to see the Sea of Tranquility”. What’s up with that? Am I remembering this wrong? Wouldn’t full moon be the best time to view any lunar feature? It always shows us the same features (lit or unlit), right? Is it just to bright in some phases? Or am I just remembering this moongazers’ advice wrong?

Okay, so a coupla weeks ago I was out looking at the moon. It was in a crescent phase, but I could faintly see the rest of it too. The crescent part was bright and beautiful, the rest of the circle was dim, but really visible. I’ve asked people about this before and they said I was imagining things. So did I make this up too? Where does the light come from that illuminates the non-crescent parts? I imagine it is bouncing off mother earth, but I guess it could be starlight too… Why does it happen sometimes but not others? Does it every happen, on a new moon, that the whole sphere is faintly illuminated, forming a ghostly “full moon” that only wise men can see?

One relatively common astonomical event I’ve never heard of is, the moon becoming new. That is, the last crescent of the moon winks out while you’re looking at it. Why don’t any amateur astronomers ever look at this? (Or do they and they just never tell me about it.) The opposite would be harder to see (the end of the new moon) since you wouldn’t really know where to look. Maybe the moon become new is just to slow and gradual to really be interesting…? Like, you’re looking at a really thin crescent, and then it’s so thin that it’s hard to see, then it’s so thin you need a telescope, and then it’s new, but the whole process took 12 hours and by then your catching “Jake and the Fat Man” reruns.

Oh crud. Apologies for all my spelling errors.
Or should that be:
O krud. A Paul, uh geez four almigh spelling air ores.
I promise never to spell Uranus with a Y.

Ooh, questions I actually know the answer to…

Well, at full moon, all the surface of the moon facing us is lit, because the sun is directly ‘behind’ us. However, when this happens, there are no shadows on the moon. Most features on the moons are just bumps, and very hard to see unless they are casting nice long shadows. If you want a good look at something in the ‘middle’ of the moon, the best time to do so is at half moon, when the shadows there are longest.

Imagine you are standing there on the Moon looking up. What do you see? The Earth, of course! When the moon is in the crescent phase, the moon is not far from straight between the earth and the moon. So most of the part of the Earth visible from the Moon is sunlit.

Yes, some people see it. It’s called a solar eclipse. See, ‘new moon’ is when we can see none of the sunlit part of the Moon, which means the sun is directly behind it.

But this doesn’t happen every month, because usually they don’t align all that well. The orbital planes are tilted a bit. So ‘new moon’ usually refers to when they are closest.

Yeah, you can see the rest of the moon during half/quarter phases. After all, it’s still there, it’s just not directly in the sun’s path. It’s quite dark but once you see it a first time, it’s pretty easy to pick out.

As for watching the moon wink out, I don’t think you meant eclipses, but rather seeing that final shift from waning to new moon. I don’t know of anyone who watches it and I doubt it’s exciting enough to become an astronomical phenomonen. But I’m sure if you were at the right moment at the right time with the right weather conditions you could watch it. You could even video tape it as long as you don’t mind taping over your Jake & The Fat Man reruns.

“I guess one person can make a difference, although most of the time they probably shouldn’t.”

You saw it. It is a real phenomenon. (Far too many people never actually look at the things they see.) The illumination would be reflected earthlight with (depending on the exact circumstance) just a hint of coronal or annular light from the sun. Starlight is much too dim to illuminate the moon. (I believe that only Venus among the stars and planets throws enough light to even cast a shadow–and that is pretty rare.) There was a faint annular glow just a couple of nights ago. (Annular is from Latin for ring, not annual from year.)


A few years ago there was an article in Sky and Telescope about this. I remember they said it was very difficult to see the moon less than 18 hours from new. I believe the reason is basically that since the moon is so close to the sun, the brightness of the sky washes it out, which makes sense.

Early one evening in the 80’s, a day after a solar eclipse, a moon that was just over 24 hours old was visible. It was a pretty odd sight because the lighted part of the moon was smaller than the smallest crescent I’ve ever seen before.

But where were the Spiders?

When people ask, of things astronomical, “What’s up with that?” The answer is always, “Everything!”

But I have a different question to ask tomndebb: How much light does something need to cast a shadow?

Ray (. . .and every time I peer above. . .everything is overcast.)

You want that in lumens?

Actually, I don’t know how much light it takes to cast a shadow. I have been out on moonless nights when I could see a faint shadow cast by Venus. (It was really faint. The object on which the shadow was cast couldn’t be too dark colored or I could not see it at all.)

I was going to try checking Jupiter’s shadow-casting powers tonight, but there is a bit of haze, here, and I can’t see any shadows.

Any astronomers, here, know which planet casts the faintest (but still visible) shadow? I’d be inclined to stick with Venus (because I have a hard time imagining anything much fainter still being visible), but I’m open to correction.


The change occurs while the moon is very close to the sun, so it is difficult to see. Unless there is an eclipse, the transition won’t be “clean”.


The term is called “Earthshine”, and it is sunlight reflected off the earth’s surface which illuminates the moon indirectly. It is a common phenomena during both waxing and waning crescent. The people you asked and doubted this were obviously not stargazers.

As for trying to observe the moon becoming “new”, first you have to understand that a very old, waning crescent moon rises VERY close to sunrise. It is very hard to detect, and it is virtually lost in dawn’s early light. You’re better bet is to try and find the youngest waxing crescent you can find. This depends on the sun’s position along the ecliptic. About a month ago, a very young crescent, just hours old, could be seen in the Western sky with an extremely reddish tint.

“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV

I should clarify that the reddish tint was NOT due to the moon’s close position to the horizon. Also, sky conditions were clear. The moon was the youngest crescent I have seen, and my interest in amateur astronomy has been “ephemeral”…no novice here!

“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV

You mean it was not caused by the Earth’s atmosphere? If so, what was it caused by?

SCR4, it must have been. My memory of the event is not as clear it should be. I’ll try to ask others who saw this with me what they recall.

“They’re coming to take me away ha-ha, ho-ho, hee-hee, to the funny farm where life is beautiful all the time… :)” - Napoleon IV

There was a lunar eclipse recently (where the earth is directly between the sun and the full moon, thus casting a shadow on the moon). I didn’t observe it closely, but I’m told by astronomers that you can detect a reddish tint on the moon just as the eclipse is starting and ending, which is caused by light refracting through the earth’s atmosphere and then hitting the moon.

He’s the sort to stand on a hilltop in a thunderstorm wearing wet copper armor, shouting ‘All Gods are Bastards!’