An eclipse is an astronomical event that happens whenever one astronomical object, Sun, Moon, planet, ect., passes either into the shadow of another astronomical object, or between the viewer and another astronomical object. There are a few different kinds of eclipses but usually us humans are only concerned, or excited, about two types, solar eclipse and lunar eclipses.
When I was a kid I remember my teacher taking us downtown to view a solar eclipse. I don’t remember the year, or if it was a total or partial eclipse, or even the name of the teacher, but I do remember looking through those eclipse glasses and thinking, this is so cool! I wondered how the glasses made it possible to look at the Sun, and I felt lucky to be alive at just the right time to see this amazing event.
A solar eclipse occurs when the Moon passes between us humans here on Earth, and the Sun. The moon will partially or totally blocks the the Sun from our view. This only happens during the time of a new Moon and the Earth, Moon, and Sun are in alignment. The Sun’s distance from Earth is about 400 times the Moon’s distance, and the Sun’s diameter is about 400 times the Moon’s diameter. These ratios are approximately the same and cause the Sun and Moon to appear to be the same size from Earth.
Solar eclipses are brief events. A total one under the most favorable circumstances lasts for about 7 minutes and 31 seconds.
What I didn’t know it while viewing that solar eclipse but these aren’t exactly rare events. In fact they happen at least twice, and up to five, times a year! It’s just that they aren’t usually total solar eclipses. Total solar eclipses are rare in any particular place because the Moon’s shadow traces such a narrow path on the Earth’s surface.
Now, if the Moon had a perfectly circular orbit, and was a teeny bit closer to Earth, and it’s orbit weren’t tilted from the Earth’s orbit around the Sun, solar eclipses would happen every month! Sadly, because the Moon’s orbit is tilted most of the time the new Moon’s shadow usually misses the Earth completely.
A lunar eclipse occurs when the Earth is between the Sun and the Moon and the Moon passes into Earth’s shadow. Unlike a solar eclipse that occurs during a New Moon, the lunar eclipse occurs only during a full Moon, a lunar eclipse can be viewed from anywhere on the night side of the Earth, and lasts for hours.
There is a special type of lunar eclipse called a selenelion. This happens when both the Sun and the eclipsed Moon can be seen at the same time! This happens right before sunset or just after sunrise when the Sun and Moon are just above the horizon on opposite sides of the sky. For that reason it is sometimes called a horizontal eclipse. It’s actually a sort of illusion because the refraction of light through the Earth’s atmosphere causes both the Sun and Moon to appear higher in the sky then they actually are.
Now, during a lunar eclipse the Moon doesn’t actually disappear into the Earth’s shadow, instead it turns a neat reddish color. This is due to the Sun’s light passing through Earth’s atmosphere, where it is scattered, before reaching the Moon. The shorter wavelengths, the purples and blues, are more likely to be scattered, while the longer wavelengths, the oranges and reds, make it through and dominate.
You might be wondering, when is the next time you might be able to view a solar or lunar eclipse in your city? Well you are in luck, timeanddate.com has a section just for eclipses. For my city, Denver, Colorado, there was a lunar eclipse this past weekend, which I forgot about and missed, and the next one is in September.
The next solar eclipse won’t occur until August of 2017, and it’s only a partial. Bummer!
Image: A total solar eclipse occurs when the Moon completely covers the Sun’s disk, as seen in this 1999 solar eclipse. Solar prominences can be seen along the limb (in red) as well as extensive coronal filaments.