By Andrew Yee, Astronomer & Nature Centre Volunteer
On August 21 a partial solar eclipse of various degree happened in North America, except the lucky places along a 110 km wide path that ran diagonally from northwest to southeast U.S. where a total eclipse was visible.
The day was sunny in the Greater Toronto Area although with haze and occasional high altitude cirrus clouds. It was hot and humid too. I took my camera and a 30+ years old telescopic “lens” to High Park Nature Centre to photograph the partial eclipse. It isn’t actually a lens but a reflector like a compact reflecting telescope. However, its optical quality isn’t built to great precision so the image quality is inferior to a modern lens of the same focal length.
I also brought a welder’s glass shade no.14 and certified eclipse glasses so Nature Centre staff and park visitors could use them to view the eclipse.
Here’s a time-lapse movie of the partial eclipse from my set of photos. There are 13 images in the sequence, with each frame taken 15 minutes apart during the eclipse. The Sun had two clusters of sunspots on that day. They are identified with their official designations at the beginning of the movie.
Irena Wilk was also at the Nature Centre to photograph the eclipse using a spare solar eclipse filter that I had. This is a mosaic of her images.
Irena brought a colander to use as a multiple pinholes projector while she wasn’t grabbing eclipse photos.
We set up on a lawn behind the Nature Centre. Kids in different summer camp groups were ready to view the partial eclipse with the pinhole projector that they made with their group leaders. Once the eclipse began a few park visitors joined us. Visitor Jackie took her young daughter and son to the park with their cereal box pinhole projectors. Everyone had a great time viewing the eclipse using different methods.
Kids found it particularly interesting using the colander pinhole projector. Even trees became giant pinhole projectors. Gaps among the leaves acted as natural pinholes to project multiple images of a crescent Sun on the path next to OURspace.
I was wrong about no noticeable change in brightness of the surrounding. While it remained very bright throughout the eclipse, the quality of light became softened and muted. I knew about the muted lighting from a total and an annular solar eclipse that I had seen before. But I didn’t think that we would see the effect even at maximum eclipse this time when the Moon covered 70.8% the area of the solar disk. And it was a surprise that the softer lighting became noticeable when the Moon blocked perhaps less than 40% the solar disk area. The muted lighting was like on a late afternoon with a layer of cirrus cloud, or an effect similar to placing a piece of diffusion sheet over a light to soften the glow in a photography or TV studio.
The pair of photos from Irena shows the muted lighting. She took both images with the same exposure time. There is no processing to either image.
The reduced lighting had a significant impact on solar energy generation. See the interesting map <http://www.skyandtelescope.co
Another interesting observation was the cooling during the deeper part of the eclipse. Irena and other visitors felt that too, so it wasn’t my imagination. At about the time we noted the muted lighting, radiant heat from the ground gradually disappeared and it was refreshing to have the relief. At maximum eclipse it distinctly felt cooler. A private weather station just north of High Park might have recorded the apparent slight drop in temperature around maximum eclipse. Here is some data courtesy the High Park Village Weather Station <http://celinmeteo.com/>: 1:11pm (eclipse began) 26.5C, 2:09pm (55.8% solar disk area eclipsed) 26.7C, 2:19pm (65.4% eclipse) 26.5C, 2:29pm (70.6% eclipse) 26.2C, 2:50pm (60.0% eclipse) 26.4C, 3:10pm(36.5% eclipse) 27.4C, 3:50pm (after eclipse) 32.5C.
I thought it would take an even deeper partial eclipse with more of the solar disk being obscured before we could perceive the cooling. Perhaps this might not be as surprising an observation when we look at weather satellite images of the eclipse. As the shadow of the Moon skirted by the Great Lakes region (the red dot on the images marks Toronto), much less sunlight reached the surface so there was more radiant heat released from the ground than its absorption from incoming solar radiation.
In fact the NASA earth-observing satellite Terra detected such a drop in surface temperature during the eclipse. The surface temperature map, courtesy NASA, for August 19 shows only a small variation across western U.S. But on eclipse day surface temperatures in central U.S. are clearly cooler during the eclipse.
Here is a different perspective of the eclipse. The very interesting time-lapse video <https://www.youtube.com/watch
The next solar eclipse that will be visible in Ontario is at sunrise on June 10, 2021. Most of the province will see a partial solar eclipse. The exception is a narrow swath that extends from northwestern Ontario northeastward to James Bay and eastern Hudson Bay. Areas in this swath will see an annular eclipse which is a special kind of solar eclipse.
What is an annular solar eclipse? The Moon goes around the Earth in an oval orbit, like most objects in the Solar System. In an oval, or elliptical, orbit there is a point where the Moon comes closest and furthest to the Earth. If the Moon passes in between the Earth and the Sun to cause a solar eclipse at the portion of the orbit that is furthest from Earth, the apparent size of the lunar disk is too small to cover the entire disk of the Sun. At mid-eclipse a ring of light surrounds the dark lunar disk and this is the annular solar eclipse.
The June 2021 eclipse is in progress at sunrise. From the Greater Toronto Area maximum eclipse happens when the U-shaped crescent Sun sits on the east-northeastern horizon at about 5:40am EDT. At this time the Moon covers 80.3% the solar disk area, and this is more blockage than the partial eclipse last week. As the Sun rises higher above the horizon, the Moon continues its march to exit the solar disk. The partial eclipse will end an hour after sunrise.
Photos by Andrew Yee, Irena Wilk and Nadine Nesbitt