Comparison

In order to understand how unique Castor is, but also in some ways how similar it is to other stars or star systems it must be compared to other stars or star systems. For this purpose the main characteristics of Castor are going to be compared to another star, or more accurately star system called Albireo (Beta Cygni). This star system is a binary system much like that of the individual Castor A, B and C systems.

Albireo is also a great favourite among amateur astronomers as it can be easily separated into its two component stars. The distance from the earth to both Castor and Albireo differ greatly, Castor being 43.7 - 51.6 light years while Albireo is 380 - 410 light years, depending on the accuracy of the measurement techniques used. This great difference in distance and coupled with the fact that Albireo can be easily separated into its two component stars, shows the great change within binary systems concerning the distance between the stars within each binary system. The distance between the two stars in Albireo is about 46AU while the corresponding distances between the binary systems in Castor are 0.022AU, 0.03AU and 0.018AU. This shows how different the distances can be between stars in a binary system. Also of note is the fact that there is 1100AU separation between all of Castors systems, showing again the great diversity within binary systems.

As would be expected the distance also determines the times of orbit within the star systems of teh stars around each other. Castor, within the sets of binary systems, has orbit times of 9.21 days, 2.93 days and 19.5 hours respectively. However the whole orbit time for the system is over 10,000 earth years. This is contrasting with Albireo, which has an orbit time of around 7,300 earth years. This great contrast within systems and with other systems shows how the orbit periods for binary systems can change greatly depending on the distances involved.

Albireo is also of interest due to the interesting contrasting star types. Most binary systems have similar colours such as Castor. Castor A and B are both shades of blue, within their binary systems, and Castor C has both red dwarfs. However Albireo has a golden yellow or 'topaz' colour star and a sapphire colour star. This contrasting colour is another reason why it is a favourite among amateur astronomers. This also shows that within a binary system there can be great differences within star types.

The magnitudes of these two star systems are also very interesting. Albireo consists of a 3.09 and a 5.11 magnitude stars. Castor on the other hand has star magnitudes ranging from 1.9 for Castor Aa to 9.1 for one of the stars in Castor C.

Another interesting point to note about these two star systems is that of the type of star system they are. Castor is a spectroscopic binary system, which means that the second star is not visible and we only know that it is there due to the wobble in the other star. However Albireo is a visual binary system meaning that both stars are visible to us and we can observe both with visual apparatus.

There is also some interesting history to compare between these two star systems. The first intriguing area is in the scientific name given to the star systems. Albireo is called Beta Cygni, beta designating that it is the second brightest star within the constellation Cynus. Castor is called Alpha Geminorum designating that it is the brightest star within the constellation of Gemini. However Castor is not the brightest star within the constellation Gemini, Pollux, its legendary brother is, so therefore it should have been given the designation beta, much like Albireo was. This would make them similar in this fashion.

The way in which both Castor and Albireo got their names is also very different. Castor as said in the history section, where it goes into it in more detail, gained its name from Greek mythology with the two twins Castor and Pollux. Albireo gained its name in a much less poetic fashion. The actual word Albireo does not mean anything in Greek or Arab where you would expect the meaning to originally come from. It is thought to have come from misinterpreting of the words 'ab ireo', written in the 16th Century edition of Ptolemy's Almagest. The Arabs also have a name for it 'Al Minhar al Dajajah', the Hen's Beak.

As can be seen from this comparison there is a great diversity among different star systems within the universe. Although both are binary systems of a sort, they contain many differences, however they also contain similarities, despite the vastness of the universe.