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This determination shows Betelgeuse to be 160 light-years from the earth. On December 13, 1920, Mr. Pease successfully measured the diameter of Betelgeuse with the 20-foot interferometer.
Pease's result somewhat, but it is almost certainly within 10 or 15 per cent of the truth. We may therefore conclude that the angular diameter of Betelgeuse is very nearly the same as that of a ball one inch in diameter, seen at a distance of seventy miles.
The heliometer parallax is doubtless less reliable than the photographic ones, and Doctor Adams states that the spectral type and luminosity of Betelgeuse make his value less certain than in the case of most other stars.
The extremely small angle subtended by this enormous disk is explained by the great distance of the star, which is about 160 light-years. That is to say, light travelling at the rate of 186,000 miles per second spends 160 years in crossing the space that lies between us and Betelgeuse, whose tremendous proportions therefore seem so minute even in the most powerful telescopes.
Yours very faithfully, In regard to the colors of stars, Miss Mitchell had already begun their study, as these extracts from her diary show: "Feb. 19, 1853. I am just learning to notice the different colors of the stars, and already begin to have a new enjoyment. Betelgeuse is strikingly red, while Rigel is yellow.
Two of the greatest of its stars, Betelgeuse and Rigel, possess, as far as has been ascertained, no perceptible motion across the line of sight, but there is a little movement perceptible in the ``Belt. At the present time this consists of an almost perfect straight line, a row of second-magnitude stars about equally spaced and of the most striking beauty.
It is also characteristic of stars believed to be in the later stages of evolution, and consequently approaching extinction, like Antares and Betelgeuse, and still more notably certain small stars which ``gleam like rubies in the field of the telescope. These last appear to be suns in the closing period of existence as self-luminous bodies.
The distant form rose lightly, skimmed low over the open area between, and grew into the grinning, freckle-faced Ban Wilson. He bounced down awkwardly, almost losing his balance, then surveyed, wonderingly, the four assistants of Ku Sui. "By Betelgeuse!" he muttered, " like robots! Horrible!" "Yes," said the Hawk shortly. "You had no trouble, eh?" Ban grinned again. "Nothing to mention.
Then after a heavy pause, "How are you getting on with the stars?" "Oh, I learned the diagrams in that nice little book you sent me, but I'm afraid I've forgotten most of them now. I feel rather superior about Betelgeuse, though." "So do I. We might start a Betelguese Club." "What would we do at it?" "Oh, read papers.
As the outer mirrors were separated the interference fringes gradually became less distinct, as theory requires, and as Doctor Merrill had previously seen when observing Betelgeuse with the interferometer used for Capella. At a separation of 10 feet the fringes disappeared completely, giving the data required for calculating the diameter of the star.
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