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Frequently Asked Questions about eclipses

Frequently Asked Questions

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What causes a solar eclipse?  As the Moon orbits the Earth, at new moon phase it passes roughly between the Earth and the Sun.  When it comes exactly between the Earth and Sun and blocks ("eclipses") the Sun, there is a solar eclipse.

How can the Moon block the Sun?  Although we think of the Sun as large, most of what we see in the sky is the glare.  The Moon and Sun are very nearly the same size when viewed from Earth!  This makes it possible for the Moon to block the Sun's light from reaching Earth when it passes in front of the Sun.

Wait...haven't I seen a total eclipse?  The last total eclipse from the US mainland was in February, 1979.  That eclipse was total ONLY in the Pacific Northwest, so in this part of the US the answer is no...all we've seen are partial eclipses.

How many eclipses happen each year?  Depending on the geometry of the Sun, Moon and Earth, there can be between 2 and 5 solar eclipses each year.  Some are total; some are only partial.

What is "totality?"  Totality occurs when the Moon completely obscures the Sun, just a few minutes of the entire eclipse.

I live where the eclipse will be 99% total.  How dark will it get?  At 99% there is still 10,000 times as much light as there is where total. It is not the same experience at all!!  Will you notice?  Sure! But there is still a lot of light even at 99%.  If you are impatiently awaiting totality, you still can NOT look directly at the Sun at 99%.  That last 1% makes all the difference. 

Will I notice a temperature drop?  Yes!  There will be opportunities for citizens to measure how much of a drop and contribute to science during the eclipse.  The drop may be as much as 10 degrees F.

What will I see during totality?  Streaming out from behind the Moon, the ethereal corona, the outer atmosphere of the Moon.  Several bright stars will be visible, and four planets (although Mars will be dim).  

Is it dangerous to observe a total eclipse?  As long as proper eye protection is used, it is safe!  It's the same Sun and Moon that are always in the sky ever day.  And of course you should never look at the Sun any day, we just need to remind ourselves of that during an eclipse, when we might me tempted. There are no "rays," no special radiation.  There is no danger to unborn children or even small children.

Can I use my solar viewers with my telescope or binoculars? NO!!  Solar viewers are ONLY for your eyes.  Never point a telescope or binoculars at the Sun unless you have proper telescope solar filters on the FRONT of these.  The solar eclipse is a visual event; you do not need a telescope.

How can we predict eclipses?  Even 2000 years ago early observers noticed that eclipses followed a repeating cycle.  This is now called a Saros cycle.  But it wasn't until Isaac Newton gave us a good way to calculate the motion of the Moon with precision that we could begin to accurately predict the path on the surface of the earth. Edmund Halley produced an early map of an eclipse path.  Today we can predict eclipse circumstances for the next several thousand years.


NASA 2017 Eclipse

Eclipse images

By Jahnc - Own work, CC BY-SA 3.0,

atlas of eclipse paths 

Eclipse paths 1981 - 2000


atlas of eclipse paths

Eclipse paths 2001 - 2020

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 Last Modified 7/7/17