Friday, August 21, 2020

Memories of the 21 August 2017 Total Solar Eclipse

Three years ago a total solar eclipse passed over the continental United States, from Oregon to South Carolina. I spent the days before the eclipse at SolarFest in Madras, OR, and saw the eclipse from a site north of Madras. It was a beautiful eclipse. Here is my best photo, using a NIKON D3100 with a 200 mm lens. You can see the three rays and even some polar rays. The three rays were much longer in person and I remember them as blue. The bright dot to the lower left is the star Regulus.

But this is a post about eclipses on other planets.

Here is an illustration of all the moons in the solar system that could cause a significant eclipse that you could see from the surface of the planet. The red arrows point to the yellow image of the Sun at Neptune, Pluto, and Eris. Even though those moons are physically small, the Sun appears to be even smaller and can be eclipsed by Triton, Charon, and Dysnomia.

The shadows of the four Galilean satellites have long been seen on Jupiter. Because the moons appear to be so much bigger than the Sun, these shadows are called occultations. An annular solar eclipse has been observed when Phobos' shadow passed over the rovers Opportunity and Curiosity.

It interesting to think about what an eclipse would be like on Neptune, Pluto, or Eris. The primary moon appears so much larger than the Sun for those planets. The amount of heat from the Sun is already a small fraction of what we receive at the Earth. Would you even notice if such a dim light was occulted?

Call them transits, occultations, or eclipses, astronomers are quite excited when one thing in the universe passes in front of another. The Kepler and TESS satellites use the dimming caused by planetary transits across their home stars to discover those planets and even study the atmosphere of the planet. Occultations of stars by Pluto were used to study the atmosphere of Pluto years before New Horizons was launched. Occultation of the New Horizons radio as it passed behind Pluto was also used to study Pluto's atmosphere. The beauty of the 2017 Total Solar Eclipse is just the icing on the cake.

Next chance for people in the US to drive to an eclipse is 8 April 2024. This eclipse will be near solar maximum. That means the corona should look more complex and interesting. I hope a spot as good as Madras can be found for that eclipse.

That was a beautiful eclipse on 21 August 2017!