Is it possible to see the full Moon and the Sun simultaneously in high northern latitudes when the Sun doesn't set? (Intermediate)

I will be going to Oslo this June. I understand that, north of some specific latitude, the sun does not set at all for one or more nights. What path does the sun follow during this time? I've heard it described as tracing a small halo over the northernmost point in the sky, never dipping below the horizon as it retrogrades back to its starting point in the circle. Is this even close?

The "critical" latitude is 66.5 degrees. But Oslo is only at 60 degrees and so you should not be seeing the "midnight sun" there.

The path of the Sun depends on the latitude of the place. At the latitude of 66.5 degrees north, the Sun will not set on June 21. On this day, the Sun rises at north, goes towards east reaching higher portions of the sky reaching a maximum elevation of about 47 degrees above the horizon at south, then go towards west and just touch the horizon (without setting) at north. Thus, the Sun never sets and goes in a circle in the sky. Now consider the extreme case of the north pole. There, the Sun will be tracing circles of roughly constant elevation for months!

Also, this year boasts a full moon on June 24. I'm intrigued by the thought of a full moon and the sun in the sky at the same time, and I was hoping to take a photograph of something I may never see again. My question: I assume the sun will be at its westernmost point in the sky when the moon rises in the east, and they will travel in opposite directions until the sun is in the east as the moon sets. How close in terms of degrees will they approach each other? That is, if the moon were directly overhead when the sun is due north touching the horizon, they would be 90 degrees apart, and I would need a pretty wide lens. Is this close to the truth?

You will almost never see the full moon and the Sun at the same time. The reason for this is that all the planets, Moon and the Sun lie in a plane in the sky called the ecliptic and this plane is tilted to the Earth's equator by about 23.5 degrees. On full moon day, the Moon and the Sun are roughly (not exactly) on opposite sides of Earth. Hence, if the Sun is at a declination of 23.5 degrees (which it will be close to summer) in the constellation of Gemini, then the Moon will be at a declination of -23.5 degrees in the constellation of Sagittarius.

Places on the Earth north of 66.5 degrees will never see the part of the ecliptic that is in Sagittarius (even though some parts of the constellation that are above the declination of -23.5 degrees may be seen depending on the latitude of the place). Hence, if you are at a latitude of say 80 degrees, the Sun will be above the sky all day during summer and the Moon will never rise during full moon.

However, the Moon's orbit is inclined to the ecliptic by about 5 degrees which is the reason why we do not see a solar eclipse during every new moon. Hence at latitudes close to 66.5 degrees, one might be able to see the Sun and the full moon for a very short time simultaneously if the geometry of the Moon is just right. However, the Sun and the full moon will be on opposite portions of the sky and so nobody will be able to photograph it unless there is an exceptional camera that can take a picture of the entire sky.

In Oslo, you will find a normal moonrise during full moon. The Sun will be up for a very long time and the full moon will rise shortly after sunset. Soon after moonrise, the Moon will set again and then the Sun will again rise. For the very same reason that you have the Sun for almost 24 hours, you will have the full moon in the sky for a very short time only.

This page was last updated on July 18, 2015.

About the Author

Jagadheep D. Pandian

Jagadheep D. Pandian

Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy. These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow. Jagadheep is currently at the Indian Institute of Space Scence and Technology.

Most Popular

Our Reddit AMAs

AMA = Ask Me (Us) Anything