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Space Physics SPACE PHYSICS Lecture 2 J. Sahraei Physics Department, Razi University http://www.razi.ac.ir/sahraei Why Space Physics? • Intrinsically fascinating! • • • • Understand the effects of the Sun on the Earth and on humans and technological systems in space (“Space Weather”) The Kepler laws of planetary motion The Second Law: The radius vector describes equal areas in equal times. Johannes Kepler, 1571-1630 The Solar System: A Better View – Eliptical Orbits Newton’s universal gravitation law Everything, whether it is as large as planets or as small as an apple, their Isaac Newton: 1642-1727 motion obey the same universal law: Sir Isaac Newton (1643-1767) Suppose we fire a cannon horizontally from a high mountain; the projectile will eventually fall to earth. Increase the velocity of the projectile, it stays longer in the air. If we keep increase the velocity, there will be a critical point, where the projectile will never able to hit the ground. Now that is exactly how moon moves relative to earth and how planets move relative to Sun. Copernicus 1513 AD (also Aristarchus, ~300 BC, but not accepted at that time) The Solar System: A Still Better View Mercury Earth Pluto Venus Mars Jupiter Saturn Neptune Uranus Asteroids Celestial Coordinate Systems How do we locate a spot on the earth? • Maps, mapquest, Google Map, GPS • If we ignore how high it 0º is above the sea • To describe a spot on the surface of the earth, we use a set of numbers (degrees), called Coordinates – Longitude – Latitude Position in Degrees –Longitude – connecting the poles, 360 degree, or 180 degree east + 180 degree West –Latitude – parallel to the equator, 0 – 90 N and 0 – 90 S 0º –A location is the intersect of a (virtue) longitude line and a latitude line 90º N Kermanshah 34°23′N, 47°03′E 0º 90º S Same idea when we describe the position of a celestial object • Celestial Sphere – An imaginary giant sphere, centered on the earth – All objects seem to be on the surface of this imaginary sphere – Earth’s poles extends and intersect with the celestial sphere as the North Celestial Pole and the South Celestial Pole – Earth’s equator extends and intersects with the celestial sphere as Celestial Equator – To locate an object, two numbers (in degrees) like the longitude and latitude are enough! The horizon coordinate system • Altitude – Angle above the horizon – 0° - 90° Meridian – The altitude of the north celestial pole equals the observer’s latitude on the earth • Azimuth – Angle measured eastward (clockwise) along the horizon, starting from the north – 0° - 360° Zenith = point directly above the observer (90o) • Meridian Note: lines of azimuth – The great circle passing through converge at zenith the celestial poles and the • Horizon zenith – The great circle whose pole is the zenith (Horizon = plane (0o)) Equatorial Coordinate System • A system in which the coordinates of an object does not change • Like the longitude and latitude on the earth, we have Right Ascension and Declination in the Equatorial system • The equatorial coordinate system rotates with stars and galaxies Equatorial Coordinate System • Declination (DEC) – A set of imaginary lines 90 ° parallel to the Celestial Equator – 0 ° at the celestial equator, increases from south to north 0 ° – negative in the southern hemisphere – Dec of the north celestial pole is 90 ° – Dec of the south celestial pole is -90 ° -90 ° Equatorial Coordinate System • Right Ascension 90 ° (RA) – imaginary lines that connect the celestial poles 0 ° – The origin of the longitude of the earth is the Greenwich Observatory -90 ° – The origin of the RA is Vernal What is Vernal Equinox Equinox? north celestial pole south celestial pole north celestial pole •We can imagine the celestial sphere as having a “celestial equator” … which is an extension of the Earth’s equator. south celestial pole Right ascension is measured in hours, minutes and seconds, because it takes approx. 1 day for a star to reappear at the same point in the sky. The equatorial system • Ecliptic – The earth revolves annually around the Sun – The Sun appears to moves from west to east on the celestial sphere – The path of the sun is called ecliptic The equatorial system • The earth’s axis is titled – line through the celestial poles is NOT perpendicular to the plane of ecliptic • 23.5 degree angle between the celestial equator and the ecliptic • The ecliptic and the celestial equator intersect at vernal equinox and autumnal equinox The equatorial system • RA – 360 degrees – Historically, use HOURS:MINS:SECS as unit – 24 hours 6 h – Starts from Vernal equinox (0 h) 0 h – increases from west to east – Stars w/ larger RA rise later Andromeda: RA: 00h 42m 44.3s DEC: +41° 16′ 9″ 6 h 0 h Vernal Equinox: RARA: 0h DECDEC: 0º Summer Solstice: RARA: 6h DECDEC: 23.5º Autumnal Equinox: RARA: 12h DECDEC: 0º Winter Solstice: RARA: 18h DECDEC: -23.5º Declination – angle from celestial equator (=0o), positive going north (north celestial pole = + 90o), negative going south (south celestial pole = - 90o) Right ascension (RA) – angle from celestial “prime meridian” – equivalent of celestial longitude RA – typically expressed as a time going east – 0 to 24 hours is 360o “Prime meridian” – point where sun is located at the vernal equinox (spring) (called vernal equinoctial colure) Ecliptic • Ecliptic – “road of the sun” imaginary path that the Sun follows on the celestial sphere over the course of a year Altitude-Azimuth coordinate system The Solar Corona: Source of the solar wind The Earth is a giant magnet The Earth’s magnetic field is a shield The Earth’s magnetosphere MAGNETOSHEATH LOBE MANTLE GEOSYNCHRONOUS ORBIT POLAR CAP PLASMA SHEET PLASMA SHEET SOLAR WIND . PLASMASPHERE AURORAE RADIATION BELTS B LOBE BOW SHOCK MAGNETOPAUSE Magnetospheric Physics.
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