Well, there’s the Land of the Midnight Sun, areas of higher latitude than the Arctic or Antarctic Circles.
To simplify the question, though, if I were at or very near either pole, would there be extended periods of time (say, weeks or months) during which the moon would be visible constantly (except for phase changes)? And other extended periods during which the moon would stay below the horizon?
If so, is there anything like the Arctic Circle for moonrise and moonset?
Thanks!
In the extreme northern and southern latitudes the moon does stay above the horizon for longer periods of time and also disappears for a few days at the time, but it’s not on a regular seasonal basis.
You can play around here US Naval Observatory and get the moonrise and moonset for any place on the planet for a whole year.
Just check Nome, Alaska for 2004 and you will see that the moon comes and goes for longer periods up there.
On a day-to-day basis, the Moon behaves roughly in the same manner as the Sun. Its path in the sky is the same as that of the Sun, or very similar, except that it’s ahead of or behind the Sun in that path. So in the Arctic and Antarctic (that is, past the Circle), the Moon can circle completely around the horizon without rising or setting.
But that’s just on a short timescale. Because the Moon travels around the Earth once a month, there is no place or time on Earth where the Moon would stay above the horizon, or below it, for more than about two weeks at a time. For example, if you’re at the Pole in summer, the New Moon will be near the sun in the sky, and therefore above the horizon (since the Sun is), but the Full Moon will be opposite the Sun in the sky, and therefore below the horizon.
Thanks, I needed that!
The USNO site is really fun! I put in 90 degrees N and saw that the moon actually stays above or below the horizon for roughly two weeks at a time, regardless of the month/season. Wow!
This whole thing came up because I was reading The Golden Compass and it has the moon rising and setting daily in an arctic region while the sun is below the horizon for weeks… so now I know that unless the moon’s orbit is tilted differently in that universe, the author got it wrong. (Even at 79 degrees N, the moon has a daily rise/set only for three days every two weeks.)
Thanks again!
The inclination of the Moon’s orbit relative to the celestial equator varies from approximately 18 to 29 degrees over a 19-year cycle known as the “regression of the nodes”. When the inclination is at the minimum of 18 degrees, any latitude above 72 degrees will experience “round-the-clock moon” (and no moon) for part of every month. When the inclination is at the maximum of 29 degrees, any latitude above 61 degrees will experience the same.
This can occur at any point in the monthly cycle of phases; when the “round the clock moon” occurs at new moon, it isn’t particularly noticeable because the moon is lost in the glare of the round-the-clock “midnight Sun” anyway.
Actually, I guess the new moon isn’t very noticeable any time, but according to the USNO site, I imagine there really is no correlation between the new moon in the sky and whether the sun is up or down, since the moon is up for about 2 weeks every month… it could be up during the months of “midday night”.
The Extreme Case: Let’s say you’re at the North Pole during winter. Assume the moon is on the celestial equator (and rising) - which would place the moon on your eastern horizon. The moon would take about 13.5 days* to cross your sky. During that time, you would probably be more conscious of the subtle change in phase - especially being in total darkness.
*It takes the moon about 27 days to return to the same spot in the sky (compared against the background stars), and half of this time it will be above your horizon.
As a rough rule for finding cases where the moon exhibits circumpolar behavior (i.e.: never setting in roughly a 24 period period) simply find where:
(90 - your lat) <= moon’s declination >= 0. In short, you’ll find you’d have to be at or above the arctic circle ( about 66.5 dgrs for the northern hemisphere) when the moon is at about +23.5 dgrs declination - now in Gemini (once was Cancer). The closer to the pole, the lower the moon’s declination can be to exhibit such behavior…until finally when you reach the pole where the moon’s declination can be greater or equal to zero declination (i.e.: on the celestial equator).
I think that’s enough for one lesson…
No. During the time of “midday night”, the two weeks that the moon is up will be the week before and after full moon. The new moon is always near the Sun in the sky, so if the Sun is up, the new moon is up (this is true regardless of latitude).
No? Actually, if I read your reply correctly, we are saying pretty much the same thing. When the sun is down for 6 months, the moon will be up for about two weeks at a time. I just didn’t realize about the new moon versus the full moon.
Herewith we present Freddy’s guide to the movements of the Sun and Moon at the North Pole.
The Sun rises shortly before the vernal equinox, and circles the sky every day in a slowly ascending spiral that peaks when the Sun is 23.5 degrees above the horizon on June 21. Then it repeats the spiral as a slow descent, finally touching the horizon shortly after the autumnal equinox and disappearing altogether on about September 26. There follow two months of slowly darkening twilight, two month of pitch blackness, and two months of slowly brightening twilight, culminating with sunrise in March, whereupon the cycle resumes.
The Moon behaves in a similar way, except that it completes the cycle of ascent, descent, disappearance, and reappearance in a month instead of a year. And, it doesn’t always peak at 23.5 degrees above the horizon; the peak varies between 18 and 29 degrees over the course of the 19-year regression of the nodes.
One question remains: How does the lunar cycle correlate with the monthly cycle of phases? It depends on time of year.
In June, the Moon rises as a waning half moon, peaks at new moon (and gets lost in the glare of the Sun), and sets as a waxing half moon. In September, the Moon rises as full, peaks as a waning half moon, and sets as new. In December, the Moon rises as a waxing half moon, peaks as full (what a glorious sight it must be, shining all day over the frozen black wasteland), and sets as a waning half moon. In March, the Moon rises as new, peaks as a waxing half moon, and sets as full.
For the South Pole, flip all of the above by six months. And bundle up—it gets mighty cold down there in July. It’s crazy cold way down there.