The Sun Today and Every Day

The Solar Dynamics Observatory (SDO) launch in early 2010 and has been studying the sun ever since. SDO focuses on understanding solar storms and the sun's magnetic field, and how all this affects us here on Earth. You can check the SDO website and see what the sun looks like every day! Today we can see a few sun spots and prominences. What will the sun look like tomorrow? We'll have to wait and see!

Image Credit: SDO

Solar Basics

 

Today we are going to cover the basics about our sun! The sun is a star, and it's the only star associated with our solar system. It's about 93million miles away from Earth, and about 110x the size of Earth. The sun is a giant ball of gas, and has a temperature of over 5800 degrees! It's corona, or surrounding gaseous "atmosphere", can get up to 2 million degrees! The suns composition is about 3/4 hydrogen, 1/4 helium, and a tiny fraction is elements heavier than helium. Fusion reactions of hydrogen into helium in the suns core release energy, which is why the sun emits light. All stars have fusion in their cores and therefore emit light. Objects such as moons and planets do not emit their own light, they reflect light from a nearby star. The sun is about 5 billion years old, and will survive for another 5 billion years. At this point, the sun will expand, engulfing the inner planets, and then shed its outer layers and create a planetary nebula. (But don't worry, that's many years away!) The image above is what the sun looks like today! (For more fun facts about the sun, see the post entitled Our Friend, the Sun)

Image credit: SOHO/ESA/NASA

Solar Neutrino Problem

Not understanding the actions of neutrinos seems to be a common theme for scientists. As discussed in last weeks ADYK, claims that neutrinos travel faster than the speed of light are currently stumping scientific theory, but neutrinos have always been mysterious particles...  

 

We discussed last week that neutrinos are neutral subatomic particles that are created in large quantities inside the sun. Astronomers in the 1940's hypothesized this, and decided to build detectors on Earth that would measure the amount of incoming solar neutrinos here on Earth. Based on the then current theories of solar fusion, astronomers predicted how many neutrinos they would expect to see in their detectors. Long story short, they measured only one third of the expected number of neutrinos, and the solar neutrino problem was born. Astronomers spent the next 50+ years trying to figure out where their theories went wrong. It was originally thought that neutrinos were massless particles, like light, and therefore existed in one form only. This turned out to be the problem, as was hypothesized by particle physicists in the 1960's and 1970's. If neutrinos had a tiny bit of mass, then quantum theory says that they have the ability to switch between three different "flavors" of neutrinos (electron, muon, tau), each with slightly different properties. If this were true, electron neutrinos would be created and released by the sun, then on their travels towards Earth, probability suggests that 33% would switch to tau neutrinos, and 33% would switch to the muon neutrinos. The detectors in the 1940's were only sensitive to electron neutrinos, and thus never detected the other two types (aka the other 66% of the missing neutrinos!). This sounded like a fantastic solution, but astronomers and physicist had to wait until the years 1962 and 2000 for the first detection of the muon and tau neutrino, respectively, thus confirming the theory. It was a long wait, but proving that neutrinos come in three flavors allowed scientists to refine the standard model of particle physics, and astronomers to really understand what was happening in the interior of stars.

Solar Spectrum

So how do we know that the sun is made mostly of Hydrogen, Helium and a handful of other elements? Astronomers use a technique called spectroscopy and here is how it works.

White light really consists of all the colors of the rainbow. You can make the colors appear by shining a light through a prism (just like the cover of that Pink Floyd album).  Astronomers use a device called a spectrograph which is mounted on a telescope and has the ability to split light into all the colors of the rainbow. What's the purpose of all this? The sun generates white light in its core as Hydrogen fuses into Helium. Each light particles (called a photon) has a slightly different amount of energy. This is what actually causes the rainbow. Red light has a certain energy, while blue light has a little bit more energy, and we perceive this energy difference as a difference in color.

 The chemical elements within the sun are made of protons, neutrons, and electrons. Thinking back to your chemistry days, the electrons orbit the outside of the atom, while the protons and neutrons make up the core or nucleus. These electrons sit in "energy levels" and light (photons) have the ability to excite these electrons to higher energy levels. When a photon hits an atom, if that light has just the right amount of energy, the electron will absorb the photon and be "excited". Electrons around different elements require different amounts of energy to get excited.

So here's the connection. If the Sun is made of lots of Hydrogen, then colors of light that excited Hydrogen electrons will be absorbed by the Hydrogen atoms in the sun. So when we look at the Sun's spectrum (above) we see black lines where color has been absorbed by different elements. These are called absorption lines. In chemistry labs we can see what absorption lines Hydrogen, Helium and other elements produce. Then when we have a spectrum from the sun, we can look for specific absorption lines from different elements and decipher what the sun is made of! Spectroscopy is used to figure out what stars are made of, along with the atmospheres of planets, and even giant clouds of gas in outer space! The image above is the entire visible spectrum of the sun. We see many absorption lines caused by Hydrogen, Helium, and other heavier elements.

Solar Composition

Most of us know that the sun is a giant ball of gas, but what exactly is it made of? Astronomers have been working on uncovering the sun's exact composition for many years, and this is the current theory...

Composite image of the sun on 9/7/2011 from the Solar Dynamics Observatory

Since different elements have different weights, we can talk about the solar composition in terms of weight. The sun weighs about 4*10^30 pounds (that's a 4 with 30 zeros after it!). About 74% of that mass is Hydrogen atoms, 25% of the mass is helium atoms, and 1% is a variety of other elements including oxygen, carbon, iron and others. Another way to think of the sun's composition is in terms of number of atoms (or volume, essentially). In these terms,  92% of the sun is filled with hydrogen atoms, about 7.8% is made of helium atoms, and that other tiny 0.2% is made of heavier elements. This composition is ever changing, as the sun is continually undergoing fusion of hydrogen into helium in its core. The sun is also shedding mass in solar wind and solar flares, but this amount is so small compared to the size of the sun that it's practically unnoticeable. Over a human lifetime the composition of the sun will stay pretty much constant.

So how did astronomers figure out what the sun is made of? Tune in later this week to find out!

Image courtesy of NASA/SDO and the AIA, EVE, and HMI science teams