* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Chapter 18 Notes I. Astronomy: The Original Science a. People in ancient cultures used the seasonal cycles of the stars, planets and the moon to mark the passage of time. b. Astronomy is the study of the universe c. Years, months and days are based on the observation of bodies in our solar system. i. Year= The time required for Earth to orbit once around the sun. ii. Month= roughly the amount of time required for the moon to orbit once around the Earth. iii. Day= the time required for the Earth to rotate once on its axis. II. Astronomy’s Founding Fathers a. Aristotle i. Greek philosopher who lived from 384 BC – 322 BC and believed that the universe was geocentric. ii. Geocentric Model= the Earth is the center of the solar system and all other bodies in space, including stars, planets and the sun revolved around the Earth. b. Ptolemy i. Greek astronomer who published a book in 140 AD that combined all of the ancient knowledge of astronomy. ii. Ptolemy agreed with Aristotle that the Earth was the center of the universe. c. Copernicus i. Polish Astronomer who was trained as a medical doctor ii. In 1543, he published a theory that the sun was the center of the solar system. iii. Heliocentric Model= the sun is the center of the solar system and the planets, including Earth, revolve around it. d. Tycho Brahe i. Danish Astronomer ii. Recorded very precise observations of the planets and stars. iii. In a duel over who was the best mathematician, Brahe had a part of his nose cut off and wore an artificial nose made of copper. e. Johannes Kepler i. Discovered that all the planets revolved around the sun in elliptical shaped orbits ii. He also discovered that the sun is not the exact center of the orbits. f. Galileo Galilei i. Italian Astronomer ii. Became one of the first people to use a telescope to observe objects in space in 1609. 1. He discovered craters and mountains on the moon, 4 of Jupiter’s moons, and sunspots on the sun. iii. Galileo was tried for heresy in 1633. His heliocentric view of the solar system went against the geocentric view of the Roman Catholic Church. 1. He was found guilty of heresy and sentenced to a number of punishments. First, he was required to denounce the theory that the Earth moved and the Sun was at the center of the solar system. 2. Second, he was imprisoned on house arrest in his villa near Florence and was allowed no visitors for the 7 years before he died. 3. Lastly, his work was forbidden to be published. g. Isaac Newton i. Showed that all the objects in the universe attract each other through gravitational forces. ii. The force of gravity depends on the mass of the objects and the distance between them. iii. His law of gravity explained why all of the planets orbit the sun- the most massive object in the solar system. h. Edwin Hubble i. Proved that other galaxies existed beyond the Milky Way in 1924 III. Telescopes a. An instrument that gathers electromagnetic radiation from objects in space and concentrates it for better observation. b. Optical Telescopes i. Most common type of telescope, includes reflecting and refracting telescopes. ii. Used to study visible light from objects in the universe. c. Refracting Telescopes i. Uses lenses to gather and focus light. ii. Have 2 disadvantages, which is why most astronomers use reflecting telescopes. 1. Images cannot be perfectly focused 2. Their size is limited, if they get too large, the image will be distorted. d. Reflecting Telescopes i. Uses a curved mirror to gather and focus light from distant objects ii. Have several advantages 1. Mirrors can be very large 2. Flaws in the glass do not affect usage 3. Images can be perfectly focused e. Light gathered by telescopes on Earth is affected by the atmosphere. i. Causes starlight to shimmer or blur ii. Light pollution from large cities can limit the ability to view far away objects. iii. Mountain tops are good locations to view the stars, because the air is thinner and there is less air and light pollution. f. Scientists have put telescopes in space, such as the Hubble Space telescope to avoid interference by the atmosphere. g. Electromagnetic spectrum i. made up of all the wavelengths of electromagnetic radiation. ii. Visible light is a small part of it, most is invisible. iii. Earth’s atmosphere blocks most of the invisible radiation from objects in space. iv. Non optical telescopes can be used to study the invisible radiation. 1. Radio telescopes- larger than optical telescopes because radio wavelengths are longer than visible light wavelengths. 2. X-ray telescopes in space are much more sensitive than optical telescopes. IV. Mapping the Stars a. Constellations i. Sections of the sky that contain recognizable star patterns. ii. Different civilizations had different names for the same constellations. iii. Today, astronomers have agreed on names and locations. iv. Every star or galaxy is located in one of 88 constellations. v. The apparent locations of the constellations change as Earth revolves around the sun. vi. Constellations are different in the southern hemisphere. b. An instrument known as an astrolabe is used to describe the location of a star or planet. c. Celestial Sphere- an imaginary sphere that surrounds the Earth. i. Astronomers use the terms right ascension and declination to plot positions in the sky much like we use latitude and longitude to plot positions on Earth. d. As the Earth spins on its axis, stars and planets appear to move. i. Circumpolar Stars- can be seen at all times of the year and all times of the night. e. Light Year i. Unit of length equal to the distance that light travels in one year ii. Equivalent to 9.46 trillion kilometers f. Doppler Effect i. Explains how we know the universe is expanding. ii. If a light source is moving quickly away from an observer, the light looks redder than normal. This is called redshift. iii. If a light source is moving quickly towards an observer, its light looks bluer than normal. This is called blueshift. iv. Edwin Hubble analyzed light from distant galaxies. 1. He discovered that all the galaxies, except our closest neighbors, were affected by redshift, indicating that they are moving away from us and that the universe is expanding.