Tonight

The colors of the stars you can see with your eyes

Rigel, Betelgeuse and Sirius in blurry dots showing the colors of the stars.
Amanda Cross of Lancashire in the United Kingdom took these photos out of focus to accentuate the colors of the stars. She said: “I wanted to compare the colors of different stars next to each other. These are stacks of Rigel, Betelgeuse and Sirius. I took individual images 60 seconds apart with ISO 16000 and speed 1/50, stacked them with Starstax and presented them together to show the different colors of the stars. I took the images deliberately out of focus to show the colors.” Thanks, Amanda!

Tonight, let your eyes adjust to the darkness and note the subtle differences in the stars, each displaying their own color. Have you ever paid attention to their various hues? Let’s explore some of the stars that you’ll see flickering against the black backdrop of night in December. There’s a whole spectrum of star colors sparkling up there, from cool red stars to middle-range yellow stars to hot blue-white stars.

The colors of the stars

In the northeastern evening sky shines a bright star with the name of Capella. Capella’s nickname is the Little She-Goat, and it lies in the constellation Auriga the Charioteer. Like brighter Sirius, which rises around 8 to 9 p.m. in the southeast, Capella often flickers deliriously when low in the sky. This effect has nothing to do with the stars themselves but rather is caused by Earth’s turbulent atmosphere. The twinkling effect is particularly prominent with the stars Capella and Sirius because they are so bright.

Can you spot Capella? If so, notice that it’s a golden star. A star’s spectral type indicates its color. Capella is a G star. Our sun is also a G star. Both our sun and Capella shine with a golden light.

Sirius – the sky’s brightest star, after the sun – is almost always described as a white star. It’s an A type star.

Night sky with ring-shaped constellation marked Auriga.
The constellation Auriga in the northeast sky at nightfall in December. The brightest star in this constellation is golden Capella. The bright red star just above the horizon is reddish Aldebaran in the constellation Taurus. Image via Till Credner, AlltheSky.com.

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The true colors of stars

The stars’ true colors are apparent when they climb higher in the sky and above the turbulence of Earth’s atmosphere. If you have good eyesight and a dark, clear sky, you should be able to detect hints of color with the brighter stars. If you have difficulty discerning star colors with the unaided eye, look at these stars through binoculars.

Try contrasting golden Capella with the reddish star Aldebaran and the stars of the misty Pleiades cluster higher up. What differences do you see?

The light of a star reveals many things, including the stars’ surface temperatures. The yellowish color of Capella indicates a mid-range surface temperature, much like our sun. The red of Aldebaran is typical of the lower surface temperature of an older star, whereas the blue of the Pleiades reveals their high surface temperature and young age.

Also have a look at the blue-white star Elnath. Officially part of Taurus, some stargazers consider it part of Auriga as well.

Diagram, graph of stars fading from blue to white, yellow, and red.
The Hertzsprung-Russell (H-R) diagram, showing the colors of stars. Image via Wikipedia.

The stars of Orion

Orion, a prominent constellation in December, sports a noticeably red star and blue star. The red star is Betelgeuse marking one shoulder, while the blue star is Rigel marking the opposite knee. Notice the shades of red and orange of Betelgeuse in the creative collage below.

Five pointed star filled with circles with varying shades of orange, red and green.
View at EarthSky Community Photos. | Soumyadeep Mukherjee in Kolkata, West Bengal, India, captured this photo of the colors of the somber red star Betelgeuse on October 14, 2021. Soumyadeep wrote: “This image shows the shades of Betelgeuse, as observed from Earth. The variation in the shades is what we call the ‘twinkling’ of a star. A star twinkles thanks to the atmospheric refraction [the same effect that causes a spoon in a glass of water to appear broken in two]. And the amount of twinkle varies due to many atmospheric factors. The effect becomes most prominent when the star is near the horizon as the light passes through more atmosphere than when near the zenith [at its highest in the sky].” Thank you, Soumyadeep!
Red cloudy patches and arcs with blue stars and one golden orange star.
This long-exposure photograph accents the colors in the constellation Orion. Image via Yuri Beletsky Nightscapes.

Bottom line: Winter is the perfect season for noticing the colors of the stars. Never noticed them? Check them out tonight!

Posted 
December 2, 2021
 in 
Tonight

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