The Solar Corona on Eclipse Day

With a quiet Sun, no active sunspot regions on the face or limb of the visible disk, one wonders what the solar corona will look like. What will we see when the Moon blots out the Sun and the corona is revealed.

MSLO K-Corona NRGF Image
The K-Coronagraph image from the Mauna Loa Solar Observatory from Aug 13, 2017
Unlike solar observers of old, we can look at the corona without waiting for an eclipse. We have both spacecraft and ground based telescopes equipped with coronagraphs. With these we can view the corona in real-time everyday!

Just up the hill from me is the Mauna Loa Solar Observatory. I know a couple folks that work there and have toured the facility. MLSO is a fairly modest telescope equipped with some very specialized instruments. This telescope stares at the Sun all day, every day, monitoring our star as part of a worldwide network of solar observatories.

For this conversation it is the coronagraph images that are interesting. With only a few days to go before the eclipse I would suspect that these images give us a good idea of what to expect.

MLSO Instruments
Ben points out various instruments on the back of the telescopes at the Mauna Loa Solar Observatory
I have posted the image for this morning, August 13, here. For the latest image you can go to the MSLO website. Check out the K-Corona NRGF image, it has been normalized to a gradient filter and may be representative of what we will see when the Moon blots out the Sun.

The dark disk in the center of the image shows where the coronagraph has blocked the direct sunlight. A dotted line indicates where the edge of the Sun would be in the image if it were visible.

You can also check out the SOHO spacecraft LASCO coronagraph. Unfortunately the LASCO occulting disk blocks more of the inner corona near the edge of the Sun.

Sun on Aug 10, 2017
The Sun as it appeared August 10, 2017 with sunspot AR2670
A quiet Sun, with no active regions or sunspots makes for a simple corona. More activity will generally be concentrated at the equator (left and right in the image) and the streamers will probably go straight outwards.

It is unlikely that there will be major prominences visible, loops and jets of hot gas visible along the edge of the Sun.

What we will actually see? That will have to wait for eclipse day to be revealed. but we can get an idea of what to expect. While we can observe the corona with instruments, the view during the total solar eclipse will be substantially better, and far more beautiful.

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

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