Sun terminology (and I’m sneaking in a cool fact or two)

Eclipses are a good opportunity to learn about the sun and its various regions. These are the regions of the sun you can see during an eclipse.

Photosphere: 

The main surface of the sun. You’ll need a proper solar filter over your eyes when any part of the photosphere is visible. The temperature of the photosphere is about 11,000° F at the bottom; 6700° F at the top. High resolution images of the photosphere show that it is made up of granules, caused by rising channels of plasma (hot gases) reaching the surface. Each of these are about 650 miles across.

Sunspots: 

Cooler regions on the photosphere. These look like dark spots on the sun. You can see them through a proper solar filter. Generally speaking, for a sunspot to be visible with no magnification, it has to be about the size of the Earth. Sunspots are inherently bright; they look dark because they are cooler than their surroundings. Sunspots tend to be more frequent (and larger) during solar maximum. Since the 2024 total solar eclipse is close to solar maximum, there is a better chance for more sunspots. 

Chromosphere: 

A thin layer of hydrogen gas just above the photosphere. It’s red, because of the wavelength of light. This can be seen for a few seconds at the beginning of totality, and for a few seconds at the end of totality- if one is deep in the path. For people that watch from closer to the edge of the path (but still inside), the chromosphere is visible for a longer period of time. The chromosphere is safe to look at with no protection, since it’s visible during totality. The temperature of the chromosphere is about 11,000 to 36,000° F. It’s about 250 to 1300 miles across.

Prominences: 

Explosions of hydrogen gas that leap out of the chromosphere. These explosions take place over the course of several hours or days, so you won’t see their motion during the few minutes of totality. They will just seem like they are still. They can have some very interesting shapes.

Corona:

The outer atmosphere of the sun. It’s searingly hot- 1.8 million° F.  You can see it as a white glow surrounding the dark disc of the moon during totality. The shape of the corona changes over time. Generally speaking, the corona is oval-shaped with long equatorial streamers during the minimum level of activity in the solar activity cycle. Solar maximum coronas tend to be more round, with streamers extending in all directions (likely for the April 2024 eclipse). Eclipses in the middle of the cycle tend to be butterfly-shaped (or similar). The corona extends millions of miles into space. 

Coronal Mass Ejection: 

Basically an explosion of a portion of the corona into space. If a coronal mass ejection hits the earth’s atmosphere, a big aurora show could occur. If a coronal mass ejection happens to be in progress during this totality, we could be on for an amazing treat!

By the way, did you notice that the temperature of the chromosphere is higher than the temperature of the photosphere just below it? The increase in temperature is relatively moderate. But notice the SIGNIFICANT temperature increase between the chromosphere and corona. That is a mystery that solar scientists have been studying for years!

Sources: 

https://www.nasa.gov/image-article/layers-of-sun/

https://scied.ucar.edu/learning-zone/sun-space-weather/sun

https://solarscience.msfc.nasa.gov








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