As a satellite in our solar system, Earth’s Moon is actually one of the larger ones, ranking 5th biggest in diameter. Only three moons of Jupiter and one of Saturn, appropriately called Titan, are larger. Ganymede, circling Jupiter, holds the number one spot at 5262 km across, half again as big as our Moon which is 3475 km in diameter. Six of the several hundred planetary satellites in our solar system are actually bigger than the former planet, Pluto, now a “dwarf planet”, which I think puts it in its proper place.
The four large moons of Jupiter are interesting to watch in a telescope as they circle the giant planet especially when one (or more) cast shadows onto Jupiter’s disk. Through our telescopes, we can actually see the shadows produced by these moons during their eclipses and can follow the dark blots as they pass across the face of the planet.
Our own Moon also casts a shadow, and being on the surface of the Earth, we have the opportunity to put ourselves inside the shadow where it appears. All this comes together during a total solar eclipse.
The solar eclipse on Aug 21 is the most spectacular astronomical event of the year and will probably be seen by millions of people. For about an hour and a half, the Moon’s 110 km wide shadow will travel diagonally across the USA from Oregon to South Carolina. Two dozen BAS members will be watching near Grand Island, Nebraska where we reserved campsites a year and a half ago. Many more casual observers in the 11 states the path crosses will likely clog up the highways to the shadow path on that date, -one estimate predicts up to 7 million people may try to get to the narrow track at eclipse time.
The Moon may be large, but it’s shadow dwindles to a tiny dot by the time it reaches the Earth and only in that very narrow path, can one say that they have “caught” the Moon’s shadow. (it’s more like letting it pass over you for the few minutes of totality). I “caught” my first Moon shadow in the clear, cold sky above Gimli, Manitoba on Feb 26, 1979, over 38 years ago, and I still get goose-bumps on the back of my neck when I think about it. The shadow could be seen moving our way and then it swept over the group creating a 360* sunset. I could not help but shiver, not from the Manitoba cold but from the experience itself. And up in the sky an incredible sight! The corona, the outer atmosphere of the Sun appeared, wispy streamers like white, irregular flower petals, surrounding a black hole, the silhouette of the Moon. More shivers!
In the Bruce-Grey area on Monday, Aug 21, only a partial eclipse will be seen since the Moon misses crossing the centre point of the Sun. The maximum is at 2:30 pm DST, when 70% of the Sun will be covered.
The partially eclipsed Sun will NOT BE SAFE TO VIEW without solar eclipse glasses like those available from FotoArt or from suppliers like Rainbow Symphony or American Paper Optics online. SkyNews magazine July/Aug issue came with a pair as an insert and it may still be available at local outlets. Also a #14 (not #12) arc welders filter will provide safe viewing. Please note, none of these filters are to be used with binoculars or telescopes, they are for naked eye viewing and only for short intervals. Please be careful with your eyesight!
From Owen Sound, some part of the Moon’s silhouette will be visible on the Sun from 1:08 pm DST to 3:45 pm DST. If you are further north or south, times may vary by several minutes, -first contact occurs later if you are north of Owen Sound’s latitude and earlier if you are south.
So if you are stuck on this local part of Earth on Monday Aug 21, at least have a quick look at the Sun with solar eclipse glasses around 2:30 pm or so. And on Sep 6 at 7 pm, you are welcome to join BAS at the Fox Observatory as we recap the event from the path of totality.
Here’s hoping for cloud-free skies (all over North America) on Aug 21!