How to calculate when the moon is highest in the sky to the earthbound observer?

Question

Like when is the new moon highest in the sky? Or third quarter? How do I know this for any general moon phase? Thanks.

Answer 1

In winter, the full moon is opposite the sun, and as the sun is low, the full moon is high.

In summer the full moon is low (for the same reasons). The crescent moon is high in summer (and low in winter) but as the crescent moon is near the sun, it is normally not visible during the day.

During spring and autumn, the sun, and the moon follow roughly equal paths, with no phase of the moon being higher in the sky.

Third quarter, being at right angles to the sun will be at an intermediate altitude, in both summer and winter.

For exact calculations either use technology, or a set of astronomical tables and a sharp pencil!

Answer 2

The Moon moves round the ecliptic. At full Moon it is opposite the Sun. Hence when the Sun is furthest South (in the Northern Winter), that full Moon is that which will be furthest North in that year and so on. But plainly, the Moon moves round the ecliptic every 28 days, so every 28 days or so it is furthest North etc.

In other words there is no answer based on phase or time of year alone.

Answer 3

Of course time of day is most correlated with moon altitude: full moon is highest around midnight, first quarter at dusk, third quarter at dawn. But the time of year is also a major factor, and can vary the altitude of a moon phase by about 46° as it moves from the top to bottom of the ecliptic.

This table works for both Northern and Southern Hemispheres:

                     moon phase      moon phase
                     HIGHEST         LOWEST
time of year         in the sky      in the sky
------------         ----------      ----------
summer solstice      new *           full (night)

autumn equinox       third quarter   first quarter
                     (morning)       (evening)

winter solstice      full (night)    new *

spring equinox       first quarter   third quarter
                     (evening)       (morning)

^{* Never stare at mister Sun!}

For example, Florida may see a full moon overhead in the December winter night sky, or the first quarter in the March spring evening. Brisbane may see a full moon overhead in the June winter night, or the first quarter in the September spring evening.

So besides time of day, time of month, and time of year, here are some other factors that affect when you can see the moon where in the sky:

• Latitude. For example, the moon can appear directly overhead only up to about 29 degrees latitude. _{(Disclosure, another answer of mine.)}
• The axial tilt of the Moon orbit, about 5° relative to the ecliptic.
• Other lunar vagaries.
• Weather, of course.

This map shows that the moon will be directly over Florida on March 20, 2040, 7pm local. (Isn't timeanddate.com amazing?) Click the map to see that the moon is in first quarter then, and other details. In this illustration, the brighter illumination is for the moon, the fainter for the sun. But I'm using it primarily to show that the first quarter moon is high in the Florida sky at that time and date. I picked that year so by coincidence the first quarter is near the March equinox, and adjusted so the moon would be right smack dab on top of Florida. But every year:

The first quarter near the March equinox is high in the sky for the Northern Hemisphere.

In the preceding sentence, flip any two italicized words for another true statement. E.g. third, March, high, Southern.