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Introduction to Astronomy and the Celestial Sphere Astrology or Astronomy? At one time, the two were considered to be the same, but branched off into mythos and science. Astrology – the non-scientific study of horoscopes. Pseudoscience Astronomy – The scientific study of the Universe. There is a big difference, but this explains why some of the terminology is similar. Revolutionary Periods in Astronomy There are two times that our understanding of the universe changed within a single lifetime. 1) 2) The 1600s- The Sun was placed at the center, and the Earth and planets orbited the Sun. Now – The Space Age. From 1957 – present. What does Universe mean? Universe- all existing matter and space considered as a whole. The totality of all space, time, matter, and energy. Can there be “other” universes by this definition? Distances are commonly measured in: inches feet centimeters miles kilometers But space is HUGE, so we use other units. Light years (9.5X1012 km) - the distance that a beam of light travels in one year Parsecs - 3X1013 km or 3.3 light years Astronomical Units (AU) 1.5X108 km – The average distance from the earth to the sun How fast is the speed of light? 186,000 miles /sec 300,000 km/s 300,000,000 m/s, which is 3X108 m/s 7 trips around the Earth’s Equator, each second! How many stars exist within 1 LY of the Sun? NONE! What is the closest star system to the sun? Alpha Centauri is actually made up of 3 stars and is 4.4 LY away from the sun Its name tells us that it is the brightest star in the constellation of Centaurus Beta is used for the second brightest Proxima is used for the closest, so our closest neighbor is Proxima Centauri Constellation of Centaurus Alpha Centauri, the brightest star in the constellation, gets the designation of “alpha” Alpha Centauri Constellation of Centaurus Beta Centauri is the 2nd brightest star in the constellation. Beta Centauri Alpha Centauri Constellation of Centaurus The 3rd brightest star in this constellation is called Proxima Centauri. Beta Centauri Alpha Centauri Proxima Centauri Constellation of Centaurus Proxima Centauri comes closer to the Earth than any other star. Beta Centauri Alpha Centauri Proxima Centauri How Many Stars in our Galaxy ? There are about 200 billion (200,000,000,000) stars in the Milky Way Galaxy. Of those 200 Billion stars, we should potentially see half of these at night (because the others are only visible from the southern hemisphere) That’s 100 billion stars But we don’t… On the clearest of nights in the city, we can only see about 2,000 stars. This is caused by light pollution Away from the city, we can only see about 6000 stars The rest are not visible because of our atmosphere, light pollution stellar dimness, distance, and our small eyes Constellations There is a natural tendency to see patterns when we play “connect the dots” with stars. These patterns are called constellations. Constellations are human groupings of stars, and can vary by culture In modern astronomy, we recognize 88 constellations 12 of these are within the zodiac 76 constellations are not. Ecliptic - represents the sun's apparent (as seen from Earth) path across the sky during the year. Zodiac - a 16° band in the sky with the ecliptic in the center. The apparent positions of the sun, moon, and most familiar planets are found within this belt. It is divided into twelve equal divisions or signs (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces). >>> FYI, in astrology, a persons sign is defined as the zodiac constellation the sun was supposedly in on their day of birth. But it’s no longer the case. Some constellations are very common. The car company, Subaru, uses The Pleides as its logo. The Pleides Also known as the Seven Sisters, the Pleides is actually about 20 stars. Is this the Big Dipper? Or is it the Big (Great) Bear? Actually, the correct name is neither The Big Dipper nor The Big Bear. These are common names that are more cultural. Its proper name is Ursa Major The “little dipper” is Ursa Minor Orion, the Hunter Notice the 3 stars of his belt Orion, the Hunter 3 stars of his belt Taurus the Bull Most constellations do not really resemble the object for which they were named instead, they were named to honor a figure from mythology which was important to the ancients. Taurus the Bull For example, does this look like a “bull” to you? There may be a resemblance, but each constellation has a cultural story • Stars within a constellation are not close to each other and are not at the same distance from Earth. So, constellations are not real places. The Celestial Sphere An imaginary shell around the earth and appears as a dome over our heads. Stars seem embedded like tiny jewels Ancient astronomers believed that all of the stars were the same distance from the earth (but, of course, they aren’t). Useful model of what we see from Earth. At any one time, we can see only ½ of the celestial sphere (Where is the other half?) Distance and Parallax Parallax – The apparent motion of an object due to the motion of the observer. Objects close to a moving observer seem to move faster than objects far away. Ancient astronomers did not see a change in the position of stars as they moved from place to place, so they knew that the celestial sphere was very high in the sky. We still use parallax as a tool to measure distances in space. Descriptions of Celestial Sphere The sky appears like a dome overhead. Zenith-directly overhead Meridian – imaginary line running north & south through the zenith Horizon – where the sky appears to intersect the ground. Altitude – height of a star above horizon (degrees) to the observer. Declination – latitude lines, extended out to celestial sphere Right ascension – longitude lines extended out into the celestial sphere. Descriptions of Celestial Sphere North Celestial Pole (NCP) – extension of Earth’s rotation axis north onto the sky. South Celestial Pole extension of Earth’s rotation axis south onto the sky. Celestial Equator – extension of Earth’s equator onto the sky. Ecliptic – apparent yearly path of Sun. It appears tilted because the earth is tilted 23 ½ degrees in space. Rising and Setting of the Stars The stars, sun, moon and planets all appear to rise in the east and set in the west. Reflection of Earth’s rotation from west to east. Our view of Celestial Sphere We live on the side of the Earth. Sky appears tilted at an angle equal to our latitude. Stars appear to move in arcs across the sky that are not perpendicular to horizon. Local Rising and Setting of the Stars We live on the side of the Earth. NCP’s altitude equals your latitude. Circumpolar stars – these stars appear close to the NCP, so they never rise or set. Instead, they circle the NCP. Depends on latitude. Polaris Polaris is more commonly known as the North Star Almost directly above north celestial pole At the North Pole, Polaris would be at the zenith Polaris is found on the northern horizon at the equator Polaris Zenith Our view of Celestial Sphere The sky appears to rotate around NCP. Altitude of NCP is always equal to your latitude on Earth's surface. Polaris At the North Pole, Polaris is found directly overhead. As the Earth rotates on its axis, all stars seem to trace out circles around Polaris. All stars at the North Pole are circumpolar and never rise or set Polaris Horizon Horizon Equator At the Equator, Polaris is found on the horizon. All stars rise and set, and none are circumpolar. Circumpolar Rise and Set In El Paso and other middle latitudes, Polaris is found between the zenith and the horizon. Some stars rise and set, and some are circumpolar. Comparing all three North Pole All stars are circumpolar Equator El Paso, TX No stars are circumpolar Some stars are circumpolar A space ship lands on an unknown planet. The occupants notice that the stars never rise or set but appear to move in circles parallel to the horizon. Where on the planet did the space ship land? a) At the equator. b) At 45 degrees latitude. c) At one of the celestial poles. d) Cannot be determine. El Paso has a latitude of about 32 north degrees. The star Polaris is very close to the Celestial North Pole. What is the altitude of Polaris when viewed from Atlanta? a) 32 degrees b) 45 degrees c) 57 degrees d) 90 degrees This picture is a time exposure of the night sky showing star trails as the stars appear to rotate around the NCP. What is the name of the bright star near the center of the rock arch? Where are the circumpolar stars? Where could this photo have been taken? Where could this photo not have been taken? How close to the Equator was this photo taken?