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StarDateYour guide to the universe Author: Billy Henry
StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky. Language: en-us Genres: Astronomy, Education, Science Contact email: Get it Feed URL: Get it iTunes ID: Get it |
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Moon and Elnath
Wednesday, 3 December, 2025
Most of the stars are so small and far away that they’re nothing more than pinpoints even in the largest telescopes. That makes it impossible to measure the size of a star. But astronomers can measure the sizes of some stars – not with a giant telescope, but with a collection of smaller ones. The technique is called interferometry. It links up several telescopes. The combo provides an especially sharp view of the heavens. If the telescopes are, say, 300 feet apart, then the combined view is as clear as that of a single telescope 300 feet in diameter. The array’s view isn’t as deep as that of a giant telescope, only as sharp. Interferometers have allowed astronomers to measure the apparent sizes of hundreds of stars. Combining that with a star’s distance provides its true size. One example is Elnath, the second-brightest star of Taurus. It’s about 134 light-years away. It’s five times the mass of the Sun. So even though it’s much younger than the Sun, it’s already passed through the prime phase of life. That’s caused it to puff up – to almost five times the Sun’s diameter. At that size, it shines more than 800 times brighter than the Sun – a big beacon for the bull. Elnath is close to the lower left of the Moon this evening. The Moon will move toward the star during the night. They’ll be closest at dawn. The gap will be smaller for skywatchers on the West Coast, and smallest for those in Alaska and Hawaii. Script by Damond Benningfield
