![]() ![]() A telescope of aperture 0.2 meters (about 8 inches) gives a resolution of 2.5 × 10 5 (5 × 10 -7 / 0.2) = 0.6 arc seconds. This accounts for the limited accuracy of the measurement of star and planet positions before the invention of the telescope.Ĭonsider a modest-sized telescope that a hobbyist might use. Visible light has a mean wavelength of about 5 × 10 -7 meters, so the resolution of the eye is 2.5 × 10 5 (5 × 10 -7 / 0.002) = 63 arc seconds or about one arc minute. ![]() What is the angular resolution of the eye? The pupil has a diameter of about 2 millimeters or 0.002 meters. In this equation, the angular resolution is in seconds of arc and the wavelength of radiation and diameter of the telescope must be in the same units. The angular resolution is:Īngular Resolution = 2.5 × 10 5 × (Wavelength / Diameter) The fundamental limit to a telescope's ability to resolve small angles is due to diffraction - the slight bending of light as it passes through a telescope. In either case, good resolution is required. ![]() Or we might want to discern details on the surface of a planet. We might want to distinguish two stars with a small angular separation. The other important attribute is resolution, or the ability to discriminate light arriving at the telescope from slightly different angles on the sky. Light-collecting area is not the entire story of a telescope. Each Keck telescope on Mauna Kea has an aperture of 10 meters, so the Keck telescope has (10/2.2) 2 = 20.7 times the collecting area of the Hubble Space Telescope. "And that helps our understanding of other stars.Hubble Space Telescope as seen from the Space Shuttle Atlantisįor another example, the Hubble Space Telescope has a mirror 2.2 meters across – this was the largest structure that could fit in the cargo bay of the Space Shuttle. "The Combiner gives us the level of precision needed to make the most accurate measurements possible of this star." "There simply wasn't the equipment available to do this kind of research," says Maestro. University of Sydney astronomer Vicente Maestro who is a co-author on the paper, says this is the most detailed study of the star to date. "Getting the data right is important for computer models which are used to study more distant stars that can't be seen as anything other than points of light." "But there were problems with the original rotational speed estimates, because at that rate Vega is at critical rotation and should be just about ripping itself apart," says Monnier. "Then about six years ago, we found out it was a rapid rotator." "We found out not too long ago that it has a disk of dusty debris, or a leftover solar system, around it," says Monnier. Vega, the brightest star in the constellation Lyra, is located 25 light-years away, making it one of the nearest stars to the Sun.Īccording to Monnier, Vega continues to both challenge and surprise astronomers. "By measuring the temperature, we could work out how fast Vega is spinning which could then be used to determine its age," says Monnier. "The greater the bulge, the further away from the star's centre it's equator is and that affects its temperature." "Because it's spinning so fast, Vega has an equatorial bulge due to centrifugal force." "This allowed us to accurately measure the temperature of Vega, which is seen almost end on from Earth," says Monnier. Using an instrument developed by Monnier called the Michigan Infra-red Combiner, the researchers were able to collect light from six telescopes, increasing the resolution to a hundred times that of the Hubble Space Telescope. They also found Vega to have about 2.15 times the mass of the Sun. Reporting in the Astrophysical Journal, Monnier and colleagues determined the star rotates once every 17 hours, rather than once every 12, as previously thought.īy comparison, the Sun's equator rotates far more slowly, about once every 648 hours or 27 days.īased on the new analysis of its rotational speed, the researchers determined Vega to be between 700 and 800 million years old, compared to the Sun's age of 4.567 billion years. Old friend The star Vega is at least two hundred million years older than previously thought, according to a new study.įor thousands of years, scientists have been using Vega as an astronomical yardstick with which to compare other stars and galaxies, as well as develop computer models of stellar life cycles.īut now, new research led by associate professor John Monnier of the University of Michigan, has found Vega is spinning slower than originally estimated, meaning the star is also older. Scientists find 'monster' star, Science Online,.Stars let us see the light, Science Online,.Early stars had a fast spin cycle, Science Online,. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |