By Diana Urbanczyk
If you caught sight of a few moonrises before, you may have noticed that the moon doesn’t rise at the same time every night. Why is that?
First, you may already know that the moon orbits Earth. Because of the nature of the orbit, the moon moves about 12 degrees to the East every day. This means that the starting place of the moonrise is that much further left of the sun.
It also means that the time at which the moon will rise lags by about 50 minutes (that’s an average; moonrise varies between about 30 and 60 minutes because of the elliptical orbit).
It may seem like the moon would never rise at the same time consistently, but the moon follows a monthly cycle. Though the day to day timings of moonrise change, the moon phases can be trusted. For example, the Full Moon. Roughly once a month, the full moon will always rise at the same time as the previous full moon. Same thing goes for the other phases.
So let’s see the schedules of different moon phases.
We may not be able to see the moon when it’s new, but it’s still out there! The cool thing about it is how it’s positioned in the same direction as the sun. Meaning that it will rise at sunrise and set at sunset (yes, during the day!).
Because we know that the moon will start its New Moon phase alongside the sun, we can actually use this information to calculate how much the moon is lagging behind the sun. If every next day the moon changes positions by 12 degrees, then the moon will lag behind the sun by 50 minutes. So, you can multiply the days since the New Moon by 50 to figure out roughly how many minutes the moon is lagging! (of course it’s all approximate because the orbit isn’t a perfect circle)
The First Quarter marks the 1/4th of the way mark of the moon’s orbit (hence the name). If you face the sun, you’ll see that the moon is now 90 degrees to left of it and lags about 6 hours behind. At this phase, it will rise in the middle of the day (noon) and set at the middle of the night (midnight).
(My personal favourite phase of the moon!)
The moon is completely opposite to the sun at this phase. This means it’s 180 degrees away and a full 12 hours behind the schedule of the sun. As a result, the moon will rise when the sun sets, and set when the sun rises. It’s easy to know what time the moon will appear in the sky when it’s a full moon because of this timing. It’s also easier to catch the beauty of a moonrise! The moon rises fast and you can clearly see the change in colours as it goes up.
During this last big phase, the moon is 3/4ths of the way through its orbit, so its last quarter (astronomers are pretty good at naming things). Facing the sun, the moon is 270 degrees to the left and lags 18 hours. Or, alternatively, 90 degrees to the right and 6 hours ahead. Since it’s the pretty much the opposite of the First Quarter, it makes sense that it rises in the middle of the night and sets at midday.
I decided to write about this after waiting almost all night for the moon. I learned all about moon orbits and timings after that night so I wouldn’t make the same mistake twice. Now that you also know all about moon phases, I hope you enjoy your moonlit nights that much more.