Descriptive Astronomy Week 4 02-02/04
Descriptive Astronomy Week 4 02-02/04 Ast 2002
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This 4 page Class Notes was uploaded by Alexa Marie on Saturday February 6, 2016. The Class Notes belongs to Ast 2002 at University of South Florida taught by Dr. Kevin McKay in Spring 2016. Since its upload, it has received 168 views. For similar materials see Descriptive Astronomy in Astronomy at University of South Florida.
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Date Created: 02/06/16
Descriptive Astronomy 02/02 Today in class we made our own “Planisphere” in order to interpret how to measure constellations by date, time, and compass. It actually takes 23 hours and 56 minutes for the Earth to spin on its axis and that makes the stars come up 4 minutes earlier. Sidereal time is reckoned from the motion of the earth relative to the distant stars. If you visit an observatory you will begin to understand why they have the coordinates the way they do by understanding sidereal time. Tells you the right ascension of the observers meridian. We continued to observe the Planisphere and Dr. McKay asked up questions about certain stars or constellations to find them on them so we know how to use the Planisphere. 02/04 An observer can only see half the sky because the Earth blocks the other half out. The high up the star is the better image you get. When star crosses meridian it is said to culminate. When stars culminate its R.A. (right-‐ascension) = local sidereal time. Circumpolar stars cross meridian twice upper and lower transit. Both sidereal and solar clock read the same time on 21 of September is because how we define the zero point. The first point of Aries The zero point for right-‐ascension is arbitrary just like the zero point. The sidereal and solar clock read opposite times on March 21. In order to define whether or not a star is circumpolar is the declination of the star has to be greater than or equal to 90 – the latitude of where you are (observer’s site). Any stars with a declination of < / (90 – lat) can never be seen. The circumpolar circle is around the pole star where these circumpolar stars reside. Exam question: The professor will give you a point and you have to find the declination of circumpolar stars. Circumpolar constellations -‐Ursa Major: The story behind this comes from Greek methology. Zeus had and affair with Calisto who then had a son Arcas. When Zeus’ wife Hera found out about Arcas she trained him to be a hunter and turned Calisto into a bear. Before Arcas made his move on the bear Zeus took the both of them and threw them into the sky. Hera had the last word and never let them sleep as the stars continue to move around. As telescopes began to get bigger with time, scientists began to find “New General Catalogue” and they’re identified by numbers. Stars are classified by colors. The sun is a “G” star. 47 Ursa Majoris is a classified “G” star and is another star that has planets circulating it. Looking out into space you can see the past and future. Low mass stars are like the sun and the amount of mass depends on how stars die. For a star like the sun is extremely stable, what will happen is it will run out of fuel and collapse. The outer layer will swell and become large. Nuclear fusion You need a lot of heat. You can turn hydrogen into helium. You need 4 H atoms to make one He atom (10 million degrees Kelvin). That’s how stars make energy. When H runs out the stars will collapse and the core will heat up. You can turn He into C. P.S.= Pole Star C.E.= Celestial equator Z= Zenith N.H./S.H.= North/South Horizon The pole star is important because it equals our latitude above the horizon. As the sun goes up the highest it can be on the day of the equinox is 23 ½ degrees for the summer solstice and -‐23 ½ for the winter solstice.
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