Astronomy for RVers
By Chris Fellows, Serenity Mobile Observatory
Correction: The eclipse starts on January 20 around 10 p.m. on the East Coast and will run till the wee hours of the morning on the 21st. Thanks to our astute readers for catching this. Our apologies for the error.
North America will be treated to this fantastic sight only once in 2019/2020. On Monday, January 21, 2019, not long after sunset, all of North America will be treated to an event that shouldn’t be missed. A total lunar eclipse isn’t exactly a rare event but jot this down on your calendar or you’ll have to wait until 2021 for the next one.
Lunar eclipses come in two flavors like any eclipse or occultation: partial and total. In a partial eclipse the shadow or body of the occulting object only partially covers the occulted object. As you may have already surmised, in a total eclipse the shadow or body completely covers the occulted object normally, making for a much more dramatic event.
This eclipse will be visible from anywhere in the country that isn’t clouded over so your chances of seeing it are good. The eclipse’s penumbra, the defuse area of the moon’s shadow, will begin at around 9:30 p.m. on the East Coast and 6:30 p.m. on the West Coast. About an hour later the umbra or sharp area of the moon’s shadow will start taking bites out of the moon’s disk. A little over an hour after that we will be in totality and the blood moon will dominate the sky. Unlike a solar eclipse that lasts only minutes and is observable at only very specific locations, a lunar eclipse will last hours, with totality lasting just over an hour, and it will be visible anywhere on the night side of the planet.
There is a great website for looking up all kinds of interesting events called Time and Date.com that you can use to determine when the event will start and how long it will last in whatever part of the country you happen to be in.
So, you may ask, why is the blood moon red? This is an interesting phenomenon and it is the same reason a sunset is red. When sunlight hits our nitrogen- and oxygen-rich atmosphere those molecules scatter blue light. This is the reason our sky is blue. The wavelengths in the part of the electromagnetic spectrum that we perceive as the color blue, 450um and shorter, can’t dive straight in but are reflected all over the place by the air we breathe.
The rest of the spectrum with its longer wavelength is less affected and comes through as yellow or white light that illuminates everything we see – except for the times near sunset or sunrise when the blue light scattering is much more severe due to the angle and thus the amount of atmosphere it is traversing to reach our eyes. At those times (angles) almost all the blue light is being absorbed or bouncing off into space so everything is pushed into the red end of the spectrum.
Now imagine that those red photons never hit your eye but went right past your head and back off into space. They would travel in a straight line and anything they illuminated would appear red. That is what is happening during a blood moon. The light from the sun is mostly blocked by the earth, but a very small amount is passing through our atmosphere, losing almost all of its blue end of the spectrum in the process, and continuing on to hit the moon making appear red. Cool, eh?
I, for one, am looking forward to this eclipse as I should still be in the desert this mid-January and have an excellent chance of getting great views. A lunar eclipse is also a great excuse to get family and friends together, have a picnic dinner and sit outside and watch the mechanics of our solar system in action.
Let me know if you observe this eclipse and what your impressions are. I know they always make me smile.
Till next time!
Chris Fellows, Serenity Mobile Observatory
Find Chris on Facebook (or, if you’re lucky, at your campground). (Editor: Check out his amazing photos on his Facebook page!)