At some points in the year, the moon at my location can be clearly visible during the day. Why is this?
If it is any help, I live in Alberta, Canada.
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4$\begingroup$ It's a common misconception that the appearance of the moon in the sky is mostly a nighttime phenomenon. Most people are familiar with the Bible verse "God made two great lights—the greater light to govern the day and the lesser light to govern the night." (Genesis 1:16) But the fact is over the course of each month, the moon spends just as much time in daytime sky as it does in the night sky. You're just less likely to notice the moon during the day. $\endgroup$– David HJan 10, 2014 at 21:09
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$\begingroup$ @David H I guess this question should more appropriately be worded, why can I see the moon on some days but not on others $\endgroup$– aman207Jan 10, 2014 at 21:13
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2$\begingroup$ You can see the moon at some times and not at others, for the same reason you can see the sun at some times and not at others. There's a big object called "Earth" between you and what you are looking at. $\endgroup$– PcManMay 22, 2021 at 0:15
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$\begingroup$ It's also possible to see some planets during the day. Venus is the easiest, particularly when it has a large angular separation from the Sun. It's also easier while the Sun is close to the horizon. $\endgroup$– Greg MillerDec 21, 2021 at 16:50
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2 Answers
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The Moon makes a full orbit around the Earth once per month. From full moon to full moon, it is 29.53058886 days (synodic month).
Full moon happens when the Moon is at one side of the Earth (right side in the image), and the Sun is at the other side. This way, Moon is fully iluminated by Sun (except in the cases where it is exactly in the opposite side of the same line, where you have a Moon eclipse). In this phase, Moon is at its highest altitude at midnight.
Then, as the Moon orbits, it comes closer to the Sun in the sky. This means both that it shows us less iluminated percentage and that its rise and set get delayed. At Last Quarter, Moon is at its highest altitude at sunrise. This means that you will be able to see the half moon figure on the sky during the morning (and last half of the night).
Then it comes New Moon, where the Moon is nearest to the Sun in the sky, and almost invisible, since it shows us the dark side during the day. Its highest altitude is at noon, but you will not be able to see it. You can, if you are lucky, see a Sun Eclipse.
Finally it comes First Quarter. To put it short, highest altitude is at sunset and you are able to see Moon during all the afternoon (and first half of the night).
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1$\begingroup$ Moon rises roughly at sunset on the day that it's full, and every night thereafter rises 52.7 minutes later than the previous day. The moon is above the horizon a bit less than half the day, every day of the month. However, it can be impossible to see during the day during its first and last phases, when it's quite near the sun. $\endgroup$ Jul 25, 2014 at 23:07
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Well, the Moon reflects quite a bit of the Sun's radiation. In fact, this person states that:
The visual geometric albedo of the full moon is 12.5%, but much less at other phases.
In combination with this, the Moon is also the closest astronomical object to us, and since the intensity of light falls off as $\propto \frac{1}{r^{2}}$ (inverse-square law), this plays arguably the biggest role in being able to see the Moon during the day. In fact, so much light from the Moon gets reflected to Earth that its apparent magnitude must be larger than the sky during the day (otherwise it would get washed out by sky noise).
According to this article, the apparent magnitude of the daytime sky is somewhere between 1.5 and 3. When you compare this to the full moon (–12.74; though you really can't see this during the day due to the geometry of the Earth/Sun/Moon system), or even a new moon at its brightest (-2.50), the Moon can almost always be seen in the sky.
