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Stars classified by color, brilliance

By Carol LutsingerMay 24, 2019

Good morning Stargazers; this week’s column will focus on star colors and how stars are classified. Although it has been cloudy more often than not, it does give us a chance to learn astronomy basics before getting to see those constellations we are missing due to cloud cover.

From our point of view on Earth most stars appear white and almost the same size and brightness. However, when the sky conditions are good, then a variety of colors and differences in brightness is quickly apparent. Using a classification system called the H-R Diagram, the stars are divided into groups according to their absolute magnitude, or brightness, and color, which is a result of the temperature and the combination of the chemical elements that comprise the star.

The temperature range is a result of the elements which give stars a color of the visible light spectral classed as O, B, A, F, G, K. M-Oh, Be A Fine Guy/Girl; Kiss Me. Using the absolute brightness and temperatures, the resulting graphic is a scatterplot of stars whose general colors are red, orange, yellow, white, and blue. Red stars are lower temperature than the blue.

When you are outside on a clear night, by midnight this month a lovely red star will be well up in the east-southeast. It will be in a group of stars that resembles a fishhook, spread-out S, or a scorpion’s body with the tail curled up defensively. Scorpius is one of the constellations that closely resembles what it represents.

The red star is the heart of the scorpion and is called Antares or Rival-of-Mars because the two are close in color. Because Scorpius rests along the ecliptic Mars is periodically passing through this constellation and a fine comparison can be made of the two. Currently Mars is in the far west at dark and sets before midnight.

To find a blue star, look for the constellation Virgo after sunset high in the southeast. Spica is very bright and rests along the eclipticat nine o’clock. This brilliant star marks the head of a sheaf of wheat carried in Virgo’s left arm. She represented abundant harvests to ancient Greeks and Romans.

An orange-appearing star is above Spica in the constellation Boötes, the Herdsman. Called Arcturus, which means Bear Guard because Boötes was assigned the task of keeping Ursa Major and Ursa Minor rotating about Polaris in the north part of the sky, Arcturus can be found using the curve of the handle of the Big Dipper in the north; “Follow the arc to Arcturus”, spike to Spica, and keep on to Corvus the Crow, as mentioned in last week’s column.

Every star we see in the night sky is bigger and brighter than our star, the Sun. The least intrinsically bright star is Alpha Centauri, which is still 1.5 times more luminous than the Sun and can only be seen with difficulty from most of our Northern Hemisphere.

Continuing with our star, the sun is a “green star” whose peak wavelength is in the transition area on the HR Diagram because its temperature is related to the predominant wavelength of emission from those elements that make up each star. The surface temperature is about 5800 K, which is green blue. Remember though, the color we actually can perceive makes it appear white or yellowish white. Please seek this website and read on.

http://blogs.discovermagazine.com/badastronomy/2008/07/29/why-are-there-no-green-stars/Red suns at sunrise or sunset are a result of sunlight passing through dust which only allows the red to orange wavelength come through. Who knew chemistry and physics could be so much fun?

Until next week, do let some stars get in your eyes.

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