Resumo de Study Of Sky

Seven stars lie within 10 light years. The nearest being Alpha Centauri.
1. Sirius
2. UV Ceti
3. Lalande 21185
4. Wolf 359
5. Alpha Centuari
6. Barnard?s Star
7. Ross 154

Above: Traveling To The Moon And Back
The Apollo 11 mission to the moon involved a complicated, carefully timed series of stages, as shown here. The journey to the moon is shown as a yellow line, while the return trip is indicated by a blue line. During orbit phases, the paths overlap. The capsule shown at splashdown is far smaller than the original craft. This is because used fuel tanks (which account for a large percentage of a ship?s bulk) were released in space as the craft traveled, and the landing module remained behind on the moon.
The Milky Way Galaxy
Our own solar system exists within one of the spiral arms of the disk-shaped galaxy called the Milky Way. This false-color image looks toward the center of the Milky Way, located 30,000 light-years away. Bright star clusters are visible along with darker areas of dust and gas.
Constellations Of The Zodiac

Ancient astronomers noted that the Sun makes a yearly journey across the celestial sphere, part of which is represented in the picture by the blue band. The ancient astronomers associated dates with the constellations in this narrow belt (which is known as the zodiac), assigning to each constellation of stars the dates when the Sun was in the same region of the celestial sphere as the constellation. The twelve zodiacal signs for these constellations were named by the 2nd-century astronomer Ptolemy, as follows: Aries (ram), Taurus (bull), Gemini (twins), Cancer (crab), Leo (lion), Virgo (virgin), Libra (balance), Scorpio (scorpion), Sagittarius (archer), Capricorn (goat), Aquarius (water-bearer), and Pisces (fishes).
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Most ancient civilizations imagined that the Sun and Moon were gods, the Earth was flat, and the sky was a dome supported by mountains. Great advances between the 5th century BC and 1st century AD proved that the earth was round. The Greeks had thought that the Sun and Moon and planets revolved around the Earth and these ideas were brought together by Ptolemy in the Almagest. In 1543 Nicholas Copernicus had a different idea. He suggested that Earth and all the other planets were revolving around the Earth. Gradually this idea gained strength though it was opposed by the Church. The process of discovery continued and Danish observer Tycho Brahe made very accurate measurements about the position of the planets. Johannes Kepler, a German astronomer used these to prove that all the planets revolve around the Sun. Kepler?s laws of planetry motion were published in 1609 and 1619. Another important step was the intoduction of the telescope by Hans Leppershey, but Galileo Galilei was the first to study the sky with it. He discovered craters on the moon and Sun-Spots.

A giant reflecting telescope completed by William Herschel in 1789
The first telescopes were refractors. A refractor uses one lens to collect light rays and another to give a magnified view. Problems with early telescopes forced astronomers to build giant aerial telescopes. Reflectors used mirrors to collect light and had some advantages over refractors.

Astrolabe
The Astrolabe was invented by the ancient Greeks to measure the position of the stars, to work out when stars would rise and set, and where they would be in the sky at different times. The device consisted of a fixed disc and a movable frame on which the brightest stars were marked. By rotating the frame, the astronomer could reproduce the apparent positions of the stars in the sky. By pointing the sighting bar, its altitude could be found.

Some Milestones In Astronomy
1. 1543: Copernicus publishes his Sun-centered theory.
2. 1576-96: Tycho Brahe observes planetary motions.
3. 1608: Invention of the telescope by Lippershey.
4. 1609: Kepler?s first law ? planets move in elliptical orbits.
5. 1609-10: Galileo?s telescopic observations.
6. 1668: Newton builds the first reflecting telescope.
7. 1687: Newton publishes his law of gravitation and motion

The ancient astronomers believed that stars were attached to a huge sphere that rotated around the Earth once a day. Nowadays, we know that they only appear to move around the Earth because the Earth itself is spinning. Even so in order to describe the position of the stars they way they rise and set, it is useful to imagine that they are fixed to a huge sphere called the celestial sphere.

The celestial sphere has north and south poles and an equator. At any time, half of the sphere is hidden below the horizon. As the sphere rotates, stars appear to trace circles around the poles. Stars close to one pole are called circumpolar as they are always above the horizon. The Sun also moves along a circle called the ecliptic.
If a long exposure is taken with a camera pointing at the pole, the Earth?s rotation causes star images to look like trails around the pole.
As the Earth moves around the Sun, the position of a nearby star changes in a regular way. The position of a more distant star changes by a smaller amount. This apparent shift is called parallax. If astronomers can measure the parallax angles knowing the distance between the Earth and the Sun, they can work out the distance from the Sun to the star.

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