Using light as a tool: images at multiple wavelengths. Solar Dynamics Observatory

Light (more formally known as electromagnetic radiation) is one of the most important tools that solar scientists have at their disposal. Radiation can tell us about the temperature, motion and composition of gases inside the Sun by using a scientific technique called "spectroscopy." The electromagnetic spectrum (EMS) is the range of all types of electromagnetic radiation, covering radio, microwave, infrared, visible, ultraviolet, x-ray and gamma-ray radiation.

Electromagnetic (EM) waves have similar properties across the whole spectrum. That means that the microwaves that heat your food, the visible light coming out of your bedside lamp, and the X-rays used to image a broken bone all have things in common: they all are forms of radiation, they all can carry energy, and they all have a wavelength associated with them.

Wavelength is a word commonly used to describe a particular type of light. When you’re looking in the visible portion of the spectrum, we refer to specific colors that our eyes register. These colors are just another way of describing wavelength. For example, instead of saying the sky is 475 nanometers, we just say the sky is blue. Similarly, rather than admiring the 650-nanometer rose, we admire the red rose. In wavelengths outside of the visible spectrum, we cannot assign color, since color is dependent on our eyes and we cannot see beyond the visible. Therefore, we group regions of the electromagnetic spectrum into bands.

Scientists—and in particular, solar scientists—make use of all of these types of light when conducting research. The Sun emits every type of radiation and we can use all of it to gather evidence in understanding what we observe.

For example, the Sun in visible light looks like a yellow/white disk (CAUTION: never look directly at the Sun. Always use protective eyewear). However, if we use special instruments to look at various wavelengths, such as ultraviolet or x-ray, the Sun can look very different. This is similar to the difference between taking a photo of a person with an infrared camera and a regular digital camera. Scientists have designed specialized instruments to pick up on these different wavelengths. In solar science, we are very interested in the ultraviolet range in particular, since this is where we can see a lot of detail. Remember that any “color” used to represent images outside of the visible spectrum has been added by scientists afterwards so we can distinguish detail. There is no color in other wavelengths.

There is a whole fleet of solar satellites observing our Sun. The Sun is the only star that is close enough that we can see detail on its surface (every other star just looks like a pinprick of light). Therefore, we can use the Sun as a testing ground for new ideas and theories to be applied to other stars.

The Solar Dynamics Observatory (SDO) is probably the one  of these satellite missions you’ve most likely heard of, or seen images from. This satellite launched in 2010 and has revolutionized how we view the Sun by taking very detailed pictures across lots of wavelengths. This means that the images are very large but that we can gather a lot more information from them than ever before.

For more information, check out the following resources:

• NASA's video tour of the EM spectrum  
• NASA's written tour of the EM spectrum
• NASA's advanced guide to the EM spectrum