By Emily Levesque, University of Washington
Neutrinos act as a window into the core of the Sun, but when it comes to the Sun as a whole it might seem surprisingly hard for astronomers to study, simply because it’s so incredibly bright! Close-ups of the Sun’s surface require carefully designed solar telescopes and observing techniques. However, there’s one fantastic way to observe the Sun without any specialized equipment—during a total solar eclipse!
Solar Telescopes: Not Easy to Design
The telescope designs are all starved for photons and are designed to carefully capture every crumb of light that comes their way from faint and distant objects. Pointing one of these telescopes at the Sun sounds ridiculous, or even downright dangerous. Designing a good solar telescope means tackling several challenges unique to the study of the Sun.
The first difficulty is that the observations need to happen during the day. This may sound obvious, and even pretty convenient, but during the daytime atmospheric turbulence is worse thanks to the Sun heating the ground, which could badly blur the pictures that are taken.
Solar telescopes can also get incredibly hot if they’re not managed correctly; the telescopes need to be cooled and need to avoid capturing any sunlight beyond what they need for their data.
Finally, solar telescopes don’t need or even want large mirrors, but large mirrors do help most telescopes capture very sharp and clear images. This means that solar telescopes are typically quite tall, staying away from the heat of the ground.
They’re also kept cool inside, with the light from the Sun focused through helium gas or a vacuum to help avoid heating the ambient air it travels through, which could also blur the image. Some of these telescopes are also very long—longer telescopes, much like wide telescopes, produce sharper images.
Telescopes: Capturing Incredible Details
Solar telescopes can observe the Sun’s surface in incredible detail. Take a look at this image of the Sun’s surface, using the same wavelengths we detect with our eyes. At first glance, it might not seem that impressive—it actually might look a little grainy! But those grains? They’re real.
If we zoom in—way in—we can see that those aren’t just blurred spots from the image; they’re actual spots on the surface of the Sun! These small patches are called granules, and some can be as small as 20 miles across.
What we’re actually seeing is the very edge of a layer of our Sun where the temperature and density conditions produce convection, the phenomenon where hotter material rises and cooler material sinks under the influence of gravity. You’ve seen something like this if you’ve ever peered into a pot of boiling water.
Hot bubbles will rise to the surface, then cool and dissipate and drop back into the pot. These granules are the protruding tops of convection cells on our Sun’s surface: the bright centers show us hot gas rising to the top of the cell, while the dark edges show us cooler gas sinking back down.
This article comes directly from content in the video series Great Heroes and Discoveries of Astronomy. Watch it now, on Wondrium.
The Total Solar Eclipse Opportunity
Another way to observe the Sun is when a total solar eclipse occurs. In a total solar eclipse, the Earth’s Moon perfectly blocks our view of the Sun’s surface, making for an incredible observing experience for anyone lucky enough to be in the path of the Moon’s shadow.
During totality, we do get a spectacular view of one part of the Sun: the solar corona, white-hot plasma with a temperature of 2 million degrees Fahrenheit that can reach many thousands of miles above the Sun’s surface.
For casual eclipse observers, viewing the solar corona is a rare and incredible sight, but for solar astronomers, eclipses offer a rare opportunity to study the detailed geometry, physics, and chemistry of the solar corona and the magnetic field of the Sun itself, which drives the corona’s appearance and shape.
Astronomers have been chasing eclipses for years—as Arthur Eddington did when he confirmed Einstein’s general theory of relativity by observing stars near the Sun during an eclipse in 1919.
An Eclipse Chasing Expeditions
One of the first people to combine eclipse chasing expeditions with digital imaging technology was astronomer Shadia Habbal. Habbal was born in Damascus, Syria. She studied physics at the University of Damascus and the American University of Beirut before moving to the United States for a doctorate from the University of Cincinnati.
Today, Habbal leads expeditions all over the world, from Kenya to Mongolia to the Arctic Circle, chasing the paths of solar eclipses. Habbal and her team carry all of the telescopes and cutting-edge imaging equipment that they need with them.
With today’s best-observing cameras and filters, Habbal can use those critical moments of totality to study things like iron atoms in the solar corona, which can trace temperature variations, map the Sun’s complex magnetic field, and offer clues linking how the Sun looks with how the Sun behaves.
Common Questions about Observing the Sun
Since the Sun is very bright, one way to observe its surface is using solar telescopes. Another way to observe and study the surface of this giant fireball is during the total solar eclipse, as the Moon blocks the view of the Sun’s surface during a total solar eclipse, creating a great opportunity for the observing astronomers.
One challenge is about using the telescope only during the daytime, which could blur the images. The other difficulty is that solar telescopes need to be cooled all the time because they can become incredibly hot.
Even though images taken by solar telescopes might look grainy, those grains are not just blurred spots. In fact, they are real spots on the surface of the Sun and are called granules. These spots can also be as small as 20 miles across.
