Star with planet.In northern spring evenings, the "twin" stars Castor and Pollux of the constellation Gemini descend the northwestern sky looking like a pair of eyes staring down at the Earth. For brightness, we see from the equation, b = L/4 p d 2, that the apparent brightness of a star is proportional to 1/d 2.Consequently, if two stars have the same luminosity, but one star is twice as far away, the more distant star will appear ¼ as bright.

Challenge your mind with Lumosity, the #1 app with 60+ brain games for memory, math, vocabulary, and more. The star is estimated to have a mass 2.15 times that of our Sun, with a radius 2.3 times as great. Castor is a white quadruple star with fairly close hot white (spectral class A) components while Pollux an orange-colored cool (spectral type K0IIIb) giant.

POLLUX (Beta Geminorum). The brightest star in the constellation is normally given the Alpha designation although there are exceptions such as Pollux which is Beta ... Castor Luminosity. The primary star of the Castor A binary pair, Castor Aa, is a main sequence blue-white star of spectral class A1 V, similar to Sirius. Castor .

Pollux, which is slightly closer to us, is a single star, while Castor is a star system consisting of six stars.

Though appearing as a single white star to the naked eye, Castor is really a remarkable multiple system, consisting of three stellar pairs. Once you know the luminosity and temperature (or color) of a star, you can plot the star as a point on the H-R diagram. The star is considered to be similar to Fomalhaut. It is a visual binary with a combined apparent magnitude of 1.58. Castor’s Distance in Perspective: Castor is about 51 lightyears away. Castor and Pollux are the two "heavenly twin" stars giving the constellation Gemini (Latin, 'the twins') its name.The stars, however, are quite different in detail. A Simple H-R Diagram. Castor Ba is estimated to have a mass 1.7 times that of our Sun, and some 1.6 times its diameter. Its absolute magnitude is 0.59 and its distance is 52 light years. Castor is a complex sextuple system of hot, bluish-white A-type stars and dim red dwarfs, while Pollux is a single, cooler yellow-orange giant. The primary star of the Castor B binary pair, Castor Ba, is a blue-white, main sequence star of spectral class A2-5 Vm. The stars, however, are quite different in detail. Castor C is an eclipsing binary system, exhibiting variations in brightness as a result of the two components periodically eclipsing each other as they orbit.

The light that we currently see from Castor left the star and began it’s journey towards Earth 51 years ago.

Castor Ba.

Castor is the second brightest star in Gemini and the 44th brightest star in the sky. Challenge your mind with Lumosity, the #1 app with 60+ brain games for memory, math, vocabulary, and more. Chapter 17 Solutions: 5. Star type. Castor or Alpha Geminorum (Alp Gem) is the 2nd brightest naked eye star in the constellation Gemini.

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Though Castor is designated as the alpha star of its constellation, it is, in fact, Pollux– Beta Geminorum – who is the brightest star. The inverse square law applies to gravity as well as apparent brightness of a star. Castor is the 24th brightest star in the night sky and the 2nd brightest star in Gemini based on the Hipparcos 2007 apparent magnitude.

The two components are separated by 6” and have a revolution period of about 467 years. Plot the luminosity on the y-axis with brighter stars going toward the top.
Castor is a complex sextuple system of hot, bluish-white A-type stars and dim red dwarfs, while Pollux is a single, cooler yellow-orange giant. Each component of the Alpha Geminorum system is in itself a spectroscopic binary star, which makes Castor a four-star system. Castor and Pollux are the two "heavenly twin" stars giving the constellation Gemini (Latin, 'the twins') its name.

Castor is a bright star in the constellation Gemini that, along with Pollux, is one of the two main guideposts for the asterism that is sometimes nicknamed "The Twins.".
A Simple H-R Diagram.