When the moon seems to be bigger than usual and have an orange tint, we call it “The Harvest Moon”. But why does this happen?
The season of fall is a point during the year when the Sun and moon are rising and setting at around the same time. (This is traditionally the season of harvest… hence the name). So, there are two parts of this question to answer:
The first part is why does the moon look bigger than usual? The truth is, it is no closer than usual and is actually no bigger than it usually appears in the sky. Things appear bigger when appearing over the horizon, but it is an optical illusion. This page offers a quick way to prove this to yourself by holding up an aspirin at arm’s length– it will cover the moon when it is at the horizon and cover just as much of the moon when held high in the sky later in the night when the moon appears smaller!
The second part is why does the moon appear orange or red? We covered this in class when speaking about lunar eclipses, and it turns out, the explanation is almost exactly the same: The atmosphere absorbs blue light and reflects red light. When the moon is on the horizon, we are seeing it through the thickest part of our atmosphere. (The sun also looks red as it is rising and setting for the exact same reason!)
