Why haven't I seen the Moon?
It has been some time since I've seen the Moon. What are the conditions that might affect whether or not the Moon is visible within a 24-hour period?
Please take into consideration any notable astronomical effects: moon phases, light pollution, other viewing conditions. I want this to be applicable to other cases as well as my own.
Here is my particular case:
I live in Wales. The date today is October 3, 2016. There has been no moon visible in the sky for the last 5 days, and I don't know why.
We just passed a new moon. Last night the moon was visible in my area as a tiny sliver. Depending on the time you were looking for it and the viewing conditions, it could in fact have not been visible.
The question is basic, but it is not trivial. Such questions of planetary motion dominated much of the last millennium in astronomy and don't see why we shouldn't provide a clear and definitive answer here.
Thank you adrianmcmenamin. It may be trivial, and I did google my question, and did get an answer. But I was hoping to get an answer from someone on here with knowledge to share with me that wasn't pre-written paragraphs. Not that I'm saying the answers were wrong or that I didn't understand.
**To all:** This question has been reopened seeking a more detailed answer to the general case, as opposed to my brief answer to the particular case in the comment above. Keep this standard in mind when you answer.
The Moon is not in the sky during a 24-hour period, the same way as the Sun isn't visible during 24 hours. Websites and newspapers show the times at which the Moon rises and sets. Between these two times the Moon should be visible. Note that they change everyday because the Moon orbits around the Earth (I think there's a 48-minute shift everyday). The reasons why you may not see the Moon is because it is too close to the Sun (around new Moon) or you're observing outside the visibility times or the Moon is too low and there are and/or building around you.
According to the NASA page about news and events related to the moon, the start of October, 2016 saw the moon enter a New Moon phase - where it is not visible, as explained on the site:
the new moon isn't visible, because it's between Earth and the sun, and the unlit side is facing Earth.
The 'unlit side' is often referred to as being the 'dark side' of the moon.
and as shown in the terribly-but-necessarily-not-to-scale diagram below:
Image source and further information: SEMS: Moon Phases
The lunar cycle is roughly 29 days (the approximate time between consecutive new moon cycles as an example). There are many online 'lunar calendars' are available, such as from Moon Connection.
However, it is just as easy to observe the lunar cycles throughout the nights (weather permitting) - when the lunar cycles are heading towards a 'new moon', then it will appear to be 'waning', 'waxing' refers to the image of the moon 'growing' towards a full moon. Examples of how the moon would appear is shown in the NASA image below:
(Image from the NASA page linked above) - the cycle progresses anti-clockwise in the diagram.
Just to add to the great answers already posted: They are all concerned with the lunar cycle and rise/set time because these are mostly what governs whether you see the Moon or not.
You mention that you also want light pollution and other viewing conditions taken into consideration and these are all near insignificant compared to the lunar cycle and rise/set time (i.e. position). While light pollution can easily prevent you from observing stars it doesn't really matter when it comes to the Moon. It is so bright that you can see it even in the crescent phases - just like you can often see the Moon during daylight. Wikipedia puts the limiting apparent magnitude in Manhattan at 2, while the Moon doesn't go above 0 (it's at around -12 at full). Actually, the best viewing conditions for astronomers are when the Moon is not visible because it is a big source of light pollution itself.
Other than that it might be cloudy but often you can catch a glimpse of the Moon or at least you can see some of the light from it through the clouds. Clouds also tend to disappear eventually so really, the most important aspects are the ones already mentioned in answers/comments. If you live near a mountain or tall buildings the Moon could certainly hide behind them but I don't think that counts.
The Moon is visible only when it is above the horizon and not too near the Sun.
Those times depend on its position in the sky relative to the Sun, and the lunar phase is related:
noon to midnight (90° east of Sun)
afternoon to early morning
sunset to sunrise (opposite Sun)
late evening to late morning
midnight to noon (90° west of Sun)
not visible (near Sun)
timeanddate.com and other sites can provide precise times of moonrise and moonset for a given location and date.