Partial Solar Eclipse

This Thursday, October 23, there will be a partial solar eclipse visible for people in the Peoria area and most of North America. Most of the world will see nothing unusual at all, and no one will get to see a total solar eclipse this time. So what's going on? 

A partial eclipse over New York City. Image Credit: Chris Cook and APOD

First, the details: 
The partial eclipse will be visible in Peoria just before sunset on October 23. The eclipse will start at 4:38 PM, when the Sun will be fairly low in the west. The Moon will only cover up the top half of the Sun, so if you do not have proper eye protection to look directly at the Sun, you will not be able to tell anything is happening at all. (You can buy eclipse shades in the Peoria Riverfront Museum Store for $1.50). By 5:45 PM, the eclipse will be at its deepest, and the Sun will be quite low on the western horizon, so find a good sunset viewing spot. The Sun sets at 6:05 PM, ending our eclipse viewing in the Peoria area. 

The solar eclipse will be low in the west southwest, so have a good view of the horizon if you want to watch it. Image credit: Stellarium.

Now, the science: 
A solar eclipse occurs when the Moon covers up the Sun from our perspective here on Earth. The Sun is 400 times larger than the Moon, but by coincidence is also 400 times farther away, so the two objects appear to be the same size in our sky. This is the reason solar eclipses can occur. Every once in a while, the Moon passes directly between the Sun and the Earth, and blocks out the sunlight for a short amount of time. 

When the Moon passes directly between the Sun and Earth, the people in the dark part of the shadow will see a total solar eclipse. Objects are not to scale. Image Credit: Wikipedia Commons.

If the Moon orbited the Earth on exactly the same plane that the Earth orbits the Sun, we would have a lunar eclipse and a solar eclipse every month (sort of like on Mars). The reason this does not happen is because the Moon's orbit is slightly tilted in relation to Earth's orbit. Usually the Moon passes just over, or just under, the Sun's path in our sky. 

Image Credit: SMU Physics

Total solar eclipses are more rare than lunar eclipses because the Moon's shadow on the Earth is much smaller than the Earth's shadow cast out into space (the cause of lunar eclipses). There is only a thin path on the Earth where a total solar eclipse is visible. This time, the Moon will totally eclipse the Sun at a spot over the north pole, so only a partial solar eclipse will be visible.

The shadow of the Moon on the Earth (and path of partial solar eclipse) is the moving oval shadow. Day and night are being shown by the other moving shadow. Image credit: NASA

If you want to see a total solar eclipse but don't want to travel very far, you are in luck! There will be one visible from Southern Illinois on August 21, 2017. Put the date on your calendar now!

A partial solar eclipse in Texas, 2012. Image credit: Jimmy and Linda Westlake and APOD.

So pick up a pair of eclipse shades or make your pinhole projector soon! Don't miss the partial solar eclipse on Thursday, October 23, beginning at about 4:30 PM, weather permitting. 

You can learn all about space and science at the Peoria Riverfront Museum's Dome Planetarium (all the shows are included with regular admission). And don't miss Wine and Cheese Under the Stars the day after the eclipse, Friday, October 24, from 7-9 PM!