Introduction To Solar Astronomy

The ancients were rather curious about this bright hot thing in the sky, and our earliest written records show a variety of theories on the subject on what the Sun precisely was, from a chariot being driven across the sky, to just another planet along the ecliptic, to a literal deity in the sky. Between the 9^th and 11^th centuries most advances were made astronomers in the Middle East. With the advent of the telescope, solar astronomy began to make serious advances, including the discovery of sunspots by Galileo. Study of the Sun's spectra followed in the 19^th century, including the discovery of helium and its subsequent naming after the ancient Greek sun god, Helios.

From there, solar astronomy has taken off in the 20^th century, using progressively better and more precise technology to garner even deeper insights into the workings of our Sun. There is a plethora of solar telescopes and solar arrays currently in operation, both in space and on the ground for a variety of wavelengths.

There are a few satellites currently out there studying the Sun as well. One of the best and oldest of them is SOHO, with instruments to study everything from solar wind density to a Doppler instrument that measures oscillations of the Sun's core. The STEREO pair of telescopes helps scientists study the Sun in, well, stereo, watching corona mass ejections and other spectacular displays from two different viewpoints.

OK, so we've all heard this one before. However, it holds true: the Sun is like an onion, not just because it'll make you cry if you look at it for too long, but because it has layers, each of which differ distinctly from each other.

The core is the critical point of the star, where nuclear fusion takes place and generates all that heat and light. This is possible due to the gravitational pressure exerted by the rest of the star, keeping it compact and thus ripe for nuclear reactions, turning hydrogen into helium.

Moving outwards, the atmosphere gets progressively less dense, but no less tumultuous. Powerful currents move within the Sun, transfering the heat through the radiative zone into the convective zone. This process creates thermal columns of rising and sinking gas as it rises and cools then sink and heat up again.

The next layer out, the photosphere, is the visible layer of the Sun: we can't directly see all those previous layers due to the photosphere's opacity—which is where all our spiffy technology comes in handy. A lot we can figure out indirectly from the action on the photosphere and from observing at different wavelengths, but nonetheless, the deep parts of the Sun are less well understand than outer laters.

Everything above the photosphere is technically considered atmosphere, mostly consisting of the corona. Oddly enough, this is the hottest part of the Sun. Long plasma filaments twist and leap into the corona, and solar wind streams out in a radioactive breeze. This part of the atmosphere is like an eternal firestorm.

This part of the Sun is typically studied with the aid of a device called a coronograph, which basically just blocks out the light from the main part of the Sun, letting astronomers look only at the light of the corona, which is otherwise hard to see.

Those convective currents within the Sun are cyclical in nature. This is most easily observed in terms of sunspots, places on the Sun's photosphere that are cooler than the surroundings. Why? Because the convective currents within the Sun have been hampered by the incredibly powerful magnetic fields that the Sun generates, which tend to twist and tangle in the corona. The number of sunspots is used as an indicator as to the amount of solar activity, and this changing number lends itself to a steady 11 year cycle. At solar minimum, there are few or no sunspots, while at maximum, there can be thousands. These are observed by solar observatories the world around, and are a huge part of solar astronomy.

There are theoretically longer term cycles as well, some of which may be responsible for climate changes of the past. However, none of these have been entirely agreed upon by the scientific community quite yet.

Solar astronomy is incredibly important to study. Without the Sun, life would not exist, so understanding its structure and cycles and how they may affect life here on Earth is incredibly important. Will the Sun emit more or less heat in the near future and cause climate change, as is theorized with the Maunder Minimum? Will a sudden increase of electromagnetic radiation fry all our electronics (and create some lovely auroras?) Is our star going to keep on burning in the near future? The Sun keeps our planet liveable, and being able to predict its moods will keep it that way.

Learning more about our particular star also helps us better understand how stars further afield work, stars that we can't as easily observe. It also gives us a great close-up look of a star at a certain time during its life cycle, and watching the Sun ever so slowly change over the history of our planet can tell us even more.

There's a lot left to learn about our Sun, a lot of mysteries to be had. Why is the corona the hottest part of the Sun, even though it's the furthest away from the part of the Sun that generates heat? How could the Sun have been bright enough to support liquid water on the surface of the Earth billions of years ago if it was still developing at that point, as all models seem to predict? Why are some sunspot minimums deeper than others, and why has the magnetic field been growing weaker? How can we predict solar wind? There are many questions about what is right in front of our faces, and solar astronomers are eager to find the answers.

Check out this article for fun facts about the Sun.

So, what's in the future of solar astronomy then, if it's so important?

There are several new solar telescopes in the works, which should help scientists considerably by providing even more accurate data. These include the ATST, GREGOR, and many more. Observational technology keeps developing in bits and spurts, and the steady stream of new telescopes will reflect that. Keep an eye out for further advances in this field!

An excellent list of major solar telescopes may be found at the Big Bear Solar Observatory website.