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Saturday, September 12, 2009


Seeing the Moon in Daylight.

The Moon in daylight. Left image, standard photo, right image, photo through polaroid glasses.

As long time readers of this blog know, I'm very enthusiastic about getting people to see Venus and Jupiter in the daylight. But did you know you can see the Moon in the daylight?

Now the dedicated astronomer types here will be going "What do you mean? Of course you you can see the Moon in daylight". Some others of you will remember a nearly full Moon rising just before sunset.

But many people have never noticed the Moon in the daytime sky. The Moon is a lot paler in the daytime sky, and can often be easily missed or or its pale aspect mistaken for a cloud. Also, for most of us living in suburban and urban settings , the sky is often a narrow band broken up by buildings or other obstructions, so seeing anything in the sky is a bit haphazard if you don't know where to look.

And of course there is clouds, we won't talk about clouds.

As well, when the Moon is at is largest, near full, it is only in the daytime sky for a short time, low to the horizon. Even today, as I write, the nearly last quarter Moon is low in the daytime sky, two hours after sunrise. Still, overall the Moon is visible in the daytime sky for a fair amount of time between full and three days before new Moon. You can actually see the crescent Moon two days before new, but it is very close to the Sun, and much care is needed (and often binoculars). In the past, I've had to use daylight Venus to help me find the thin crescent!

To find the Moon in the daylight it helps to have a good idea of where it is at night. After full it is relatively easy, you can see where the Moon is just before Sunrise, and can keep an eye on it after Sunrise. In the daylight, a lot of the moons features are easier to see with the unaided eye, as they are not lost in the glare of the Moons brightness. You can use polaroid glasses or filters to help see the Moon. Unlike Venus, whose light is strongly polarised, using polaroid filters cam increase the contrast between the Moon and the sky quite significantly (the images above don't do the actual increase justice).

Before full, you can use a newspapers Moon rise and set times (often up the back) or set of astronomical tables (or tide time tables) to find when the Moon rises, and scan the sky (wearing polaroid glasses if you like) for the Moon. Or you could see where the Moon is the previous night just after sunset, then, remembering that the Moon is around two hand spans further on each night, look in the approximate position the Moon was the next day (but two hand spans over).

We often think that astronomical activities cease when the Sun rises, but for the Moon and bright planets, it's not really over. Happy Moon hunting!

This is the fifth of a planned series of posts on looking at the sky and how to find your way around it as a beginner.

First post: The Dark Adapted Eye.
Second post: Let the Moon be Your Guide
Third Post: Seeing the Emu.
Fourth Post: Cloudy, Cloudy Sky

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I was just surfing through blogs and came across yours. My 6 year old loves it! He's loves learning about planets. We'll be visiting here more often!
I'll be doing some kid specific posts in the near future, so I hope your 6 year old will enjoy them.
I have seen Venus before sunset when it is close to its greatest brilliancy. last week I saw it shortly after sunset with the naked eye in the twilight. I am located at Longitude 51.5 N, Longitude zero.

Hi just seeing if any one knows why a crest of a daytime moon appears and not the full moon sometimes as I thought that if the moon is visible during the day wouldn't it be the whole moon as the sun light would be reflecting off of it making it a full daytime moon?
Hey does any one know why sometimes a daytime moon is not a full moon and is seen as a crest only as I thought the daytime moon would always apear full as the sunlight would be reflecting off of it
Hey Ian why does the daytime moon sometimes apear as a crest or half moon and not a full moon? I thought if the sun was up as well it would reflect off of the whole moon?
To be a fool Moon, the Moon has to be directly opposite the Sun, rising at as the sun sets, and setting as the sun rises. So a full Moon can never be seen during the day (all other Moons rise before sunset or set after sunrise.
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