Open Questions

The diamond-ring effect on the 2017 eclipse. Image Credits: Carla Thomas, NASA

Why is the solar corona so much hotter than the surface of the Sun?

As discussed in our solar corona page, the outer atmosphere of the sun, the corona, is up to 300 times hotter than the actual surface of the Sun. So why is this? Despite not having a clear answer, scientists do have some theories. Jim Klimchuk, Goddard Space Flight Center, Greenbelt, Maryland, who works for NASA, suggests that regular, small explosions he calls ‘nanoflares’ may be responsible for the rise is temperature. These explosions are measured as even hotter than the temperature of the corona and could be responsible for the increased temperature.

This is also an active topic of research within the Solar and Magnetospheric Theory Group at the University of St Andrews. If you’d like to read more about solar research at St Andrews and how the study of solar eclipses help with that research, you can find a summary here.

A photograph of the Sun. On either side of the photo is three images that should the separated wavelengths of light, which correspond to different colours.
“NASA’s EUNIS sounding rocket examined light from the sun in the area shown by the white line (imposed over an image of the sun from NASA’s Solar Dynamics Observatory) then separated the light into various wavelengths (as shown in the lined images – spectra – on the right and left) to identify the temperature of material observed on the sun. The spectra provided evidence to explain why the sun’s atmosphere is so much hotter than its surface.” Credits: NASA/EUNIS/SDO, sourced from NASA.

Do other planets experience solar eclipses?

Is the Earth the only planet in the Solar System to experience solar eclipses? We might think it is a phenomena that is unique to our planet, but this is actually not the case. As we know from our experience on Earth, an Eclipse occurs when the moon (or in fact any moon!) obstructs the Sun’s light from reaching the face of the planet. This can happen all across the Solar system as natural satellites (Moons) are by no means unique to the Earth.

Mars' largest Moon partially obscuring the Sun, causing a solar eclipse. The Moon is much smaller than Earth's and isn't spherical, so it doesn't fully obscure the Sun.
This is an image of an Annular Eclipse taken by the Mars Curiosity Rover during August 2013. It shows Mars’ largest moon, Phobos moving across the Sun. Credits: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M University.
Jupiter, captured from a distance, has three dark circular spots on it. The spots are shadows caused by Sunlight being blocked by Jupiter's Moons.
The Hubble Space telescope captured 3 Solar Eclipses simultaneously occuring on Jupiter caused its biggest moons, Castillo, Ganymede and Io. Credits: NASA, ESA, & E. Karkoschka (University of Arizona).

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