Puma Espera White Arcturus - 4th B Cheap Puma Espe

ausn0qld0gm · Wysłany: Czw 6:03, 31 Mar 2011

Astronomers calculate that Arcturus has been visible to the unaided eye from Earth for only the past half million years. During that time, it has been moving closer to us on its way towards Virgo. Arcturus is now near its closest point to us and in a few thousand years will pass by. As it then moves away, Arcturus will slowly dim from our view. In another half million years, this very bright member of our current skies will no longer be visible from Earth.
The Big Dipper is in fact quite useful in finding Arcturus. After locating the Big Dipper in the sky, simply follow the curve of its handle, which points to Arcturus. Many people remember this as “arcing to Arcturus.”
Read on
How Stars Got Their Names
The Night Sky on July 3 and July 4 2010
Getting Started In Astronomy: Big Dipper Sign Post
Arcturus and the 1933 World's Fair
Astronomers believe Arcturus formed about 10 billion years ago. This makes it twice as old as our sun, and the oldest object easily visible with the unaided eye. It is a red giant star visible in the early evening from spring though fall. It is estimated to be 20 million miles in diameter - 25 times that of the sun - and about 115 times as luminous as the sun.
Science of Arcturus
Arcturus means the “guardian of the bear.” It is the brightest star in the constellation Boötes, the Herdsman. This group of stars depicts the herdsman driving the bears (in the nearby constellations Ursa Major and Ursa Minor - the big and little bears) across the sky.
Not counting the sun, Arcturus is the fourth brightest star in all of the sky as viewed from Earth, behind Sirius (constellation Canis Major - the Big Dog), Canopus (constellation Carina - the Keel) [link widoczny dla zalogowanych] and Rigil Kentaurus, better known as Alpha Centauri (which is a binary star in the constellation Centaurus [link widoczny dla zalogowanych], the Centaur.) These other three stars are in more southern skies; Arcturus is the brightest star north of an imaginary line known as the celestial equator, a projection in space of Earth’s equator.
The fair organizers used Arcturus because at the time, scientists believed it was 40 light years away. Thus, the light used to trigger the opening of the fair began traveling to Earth 40 years prior, in 1893. Since a similar fair had been held in Chicago in 1893, organizers saw this as a perfect unifier of the two events - light that began traveling toward us during the 1893 event arrived to commence the 1933 event.
Furth
Today, we have a more accurate estimate of Arcturus’s distance (36.7 light years, as calculated by the European Space Agency's Hipparcos Space Astrometry Mission) than the one postulated in 1933. However, this does not diminish its role in the 1933 fair, its significance as an important celestial object, or its prominence in the current night sky.
In 1933, Arcturus became famous for its association with the Century of Progress World’s Fair held in Chicago that year. To honor the theme of progress [link widoczny dla zalogowanych], organizers decided to incorporate new technologies to kick off the fair. Using the 40-inch refracting telescope at Yerkes Observatory, they collected light from Arcturus and focused it on photoelectric cells, activating switches that turned on the World’s Fair lights.
Arcturus was purportedly the first star seen during daytime - in 1635, a couple decades after Galileo first pointed a telescope skyward. Around 1718, Edmond Halley compared the positions of three stars - Arcturus, Sirius and Aldebaran - versus those given by ancient Greek observers, and found that their positions had all changed. This marked the discovery of “proper motion,” which relates to the fact that stars are not permanently fixed in space.