APOD: 2021 July 21 - Colors: Ring Nebula versus Stars

Good morning, Rallypoint. Today's Astronomy Picture of the Day (APOD) is titled "Colors: Ring Nebula versus Stars." A diffraction grating is an optical component that splits and diffracts visible light into several beams travelling in different directions. If you've seen a rainbow, you've seen a diffraction grating. Today's APOD takes that principle and applies it to the Ring Nebula (M57) and its surrounding stars in the constellation Lyra.

The parent star of the Ring Nebula is a star in the last stages of its evolution, where it has expelled a luminous envelope of ionized gas into its surrounding region. This gas cloud is referred to as a planetary nebula. Through the diffraction grating we see that the presence of hydrogen (red) and oxygen (blue) is indicated, and just to the right of center is the combined visible light as seen from an unfiltered source.

But why is the Ring Nebula surrounded by a bunch of streaks? M57 is only 2,000 light years away from Earth. The stars surrounding the Ring Nebula are much further away. Thus, there is some distance between the colors of M57, while the stars appear as separate streaks. But if you look, you can see differences between each of them. For example, some have very prominent red segments while others have none. This data can suggest the presence (or lack of) certain elements, or the motion of the object relative to the viewer (either towards or away from you). The amount of redshift (towards the left of each streak) can also indicate how far away the object is from the viewer.

As you can see, a basic knowledge of light and wave mechanics occasionally comes in handy. And some people say Space is boring.