Early history of astronomy. Early history of astronomy. Positions in the sky. Lecture 3: The Sun & Constellations

Transcription

1 Lecture 3: The Sun & Constellations Professor Kenny L. Tapp Early history of astronomy Birth of modern astronomy Noted scientist Johannes Kepler ( ) Ushered in new astronomy Planets revolve around the Sun Laws of planetary motion Orbits of the planets are elliptical Planets revolve around the Sun at varying speed Early history of astronomy Birth of modern astronomy Noted scientist Galileo Galilei ( ) Supported Copernican theory Used experimental data Constructed an astronomical telescope in 1609 Four large moons of Jupiter Planets appeared as disks Phases of Venus Features on the Moon Sunspots Positions in the sky Astronomical coordinate system on the Celestial Sphere Stars appear to be fixed on a spherical shell (the celestial sphere) that surrounds Earth Equatorial system of location A coordinate system that divides the celestial sphere Similar to the latitude-longitude system that is used on Earth's surface Two locational components Declination the angular distance north or south of the celestial equator Right Ascension the angular distance measured eastward along the celestial equator from the position of the vernal equinox Figure 21.16

2 Earth motions Two primary motions Rotation Turning, or spinning, of a body on its axis Two measurements for rotation Mean solar day the time interval from one noon to the next, about 24 hours Sidereal day the time it takes for Earth to make one complete rotation (360º) with respect to a star other than the Sun 23 hours, 56 minutes, 4 seconds The difference between a solar day and a sidereal day Figure Earth motions Two primary motions Revolution The motion of a body, such as a planet or moon, along a path around some point in space Earth's orbit is elliptical Earth is closest to the Sun (perihelion) in January Earth is farthest from the Sun (aphelion) in July The plane of the ecliptic is an imaginary plane that connects Earth's orbit with the celestial sphere Gradual change in size of Sun Now 40% brighter, 6% larger, 5% hotter

3 Solar Prominence Solar Flares Astronomy Picture of the Day Solar Wind NASA.gov Auroras are caused by the solar wind. Auroras on Saturn

4 The Constellations Star patterns named by ancient peoples after gods, goddesses, animals, monsters, and mythic heroes. The constellations used by Western Culture today originated in Mesopotamia around 3,000 B.C. Today 88 constellations are recognized The brightest stars in a constellation are identified in order of their brightness by the letters of the Greek alphabet alpha, beta, and so on Circumpolar Constellations Always above the horizon (though often very low) Everything with declination higher than 90º minus your latitude (90-35 = 55ºN for us) For us: Ursa Minor, Ursa Major, Cassiopeia, Cepheus, & Draco Polaris: The North Star "Barely moves with time of day or season Its altitude = your geographic latitude A double star A cepheid variable star""" "How"to"Find"it:"" From the Dipper, follow the two stars at the end of its bowl toward Cassiopeia. There, about five times the separation of these two stars, you'll find Polaris. Use the middle three stars of Cassiopeia's "W" as an arrow to point in the direction of the Dipper. Halfway there you will encounter Polaris. 21"March" :00"PM The"Spring"Sky (Oklahoma City, OK) Big Dipper Polaris (North Star) (Oklahoma City, OK) Polaris (North Star) Venus Orion constellation (winter only) Cassiopeia Ursa Minor Big Dipper/Ursa Major

5 This Month s Sky Map Download from Course Website --> Next Time