changing face of the sun
January 23, 2013

The Changing Colors Of The Sun

Lee Rannals for — Your Universe Online

When we take a glance at the sun, or sit down with paint to color the sky, we always see our home star as yellow, but the sun is full of much more diversity.

The reason we only see yellow is because it is the brightest wavelength of light from the sun, but with special instruments, NASA is able to see all the wavelengths.

With these instruments, whether they are in ground-based or space-based telescopes, we can observe light far beyond the ranges visible to the naked eye. Different wavelengths help scientists to gather more details about different components of the sun's surface and atmosphere. Scientists are able to use these details to capture a better image of our constantly changing star.

The sun emits a yellow-green light of 5500 Angstroms, which emanates from material about 10,000 degrees Fahrenheit. At this temperature, we are actually looking at the surface of the sun as well.

Extreme ultraviolet light of 94 Angstroms comes from atoms that are about 11 million degrees Fahrenheit, which is also a good wavelength to catch solar flares in action. This wavelength shows the sun in a lime green color.

NASA is able to look at pictures of the sun at a variety of wavelengths through telescopes like its Solar Dynamics Observatory (SDO), Solar Terrestrial Relations Observatory (STEREO) and the Solar and Heliospheric Observatory (SOHO).

The visible spectrum of light is seen because the sun is made up of a hot gas, but the shorter wavelengths take place when the sun sends out extreme ultraviolet light and x-rays. The sun does this because it is filled with all kinds of atoms, each of which give off light of a certain wavelength.

"Not only does the sun contain many different atoms — helium, hydrogen, iron, for example -- but also different kinds of each atom with different electrical charges, known as ions. Each ion can emit light at specific wavelengths when it reaches a particular temperature," NASA wrote in a feature entitled "Why NASA Scientists Observe the Sun in Different Wavelengths."

Spectrometers help scientists observe many wavelengths of light simultaneously, measuring how much of each wavelength of light is present. This helps to create a composite understanding of what temperature ranges are exhibited in the material around the sun.

Instruments that produce conventional images of the sun focus on light around one particular wavelength. Scientists chose 10 different wavelengths to observe with the Atmospheric Imaging Assembly (AIA) instrument. Each wavelength is based on either one or two types of ions and were chosen to highlight a particular part of the sun's atmosphere.

For a more aqua color of the sun, one must observe it in 131 Angstroms. This brilliant color actually represents the hottest material in a solar flare. The SDO helps to image the sun in purple as well, when looking at 211 Angstroms. This wavelength shows hotter, magnetically active regions in the sun's corona.

A more earthy tone, brown, can be seen at 171 Angstroms, which is the wavelength that shows the sun's atmosphere when it's quiet.

NASA's instruments really help unveil more than we've ever known about our closest star, giving insight into space weather and an understanding of other stars in the Universe.