Astronomy : The study of sky ( night )

1. Astronomy : The study of sky ( night ) Human beings fascinated by night sky. Sun , Moon, Planets and fixed stars Planets (wanderers) Celestial sphere Planets on different spheres Geo-centric view Ptolemy Copernicus, Gallileo Observations Helio-centric view

2. The vast majority of the objects in the night sky – Stars Co-ordinate system needed to specify position. Diurnal motion of stars – but they maintain fixed separation between them. Concept of Celestial sphere, rotating around an axis passing through Celestial pole The apparent motion is a consequence of Earth’s rotation and revolution in an orbit around the Sun. The geographical latitude of the place of observation plays a major role in the appearance of the sky. Great circles and small circles Celestial Equator and Ecliptic Zenith, Meridian, First point of Aries Altitude of the North Celestial Pole - Geographical latitude Circumpolar stars

3. Co-ordinates to define the position of a star Azimuth – Altitude ( Zenith distance ) Right Ascension – Declination Hour Angle –Polar Distance Celestial Latitude & Longitude Z Azimuth : 0 – 180 deg E, W ,Measured from N, along horizon Altitude : From Horizon towards Zenith along a great circle thru the body and Z. Zenith dist = 90 –Alt These co-ordinates change with time. P * S N Right ascension : along Celestial equator from first point of Aries – anti clockwise ( degrees or hours) Declination : 0-90 deg, N or S Along the great circle from equator thru the body to pole. E

4. First point of Aries : Intersection of the ecliptic and the Celestial equator. Ecliptic is the orbital plane of the Earth. So apparent yearly motion of the Sun is along the ecliptic. Diurnal motion of the Sun as well as other stars are in small circles parallel to the equator On March 21, vernal equinox , the Sun is at the First point of Aries. It moves along the equator on that day. Hour angle : Measured from the meridian along the equator Polar distance : Angle of the body from the pole along the declination circle. Celestial latitude and longitude : wrt ecliptic and with respect to pole of ecliptic.

5. Constellations :88 constellations - Specific area of the skyNames of stars – use Greek letters – e.g. aOrionisAlso proper names e.g. Betelgeuse Brightness in terms of magnitudes Magnitude 1 to 6 - Brightness 100 :1 . Log Scale Brighter objects – Magnitude 0 and –ve Intensities measured by photometer

6. Magnitude ; b, br, ……..br5 r= 1001/5 bm/bn = 10.4 (n-m) Thus relative intensity of stars being known , the magnitude of one can be calculated if the magnitude of the other is known. Absolute magnitude : Apparent magnitude of the star is what we see. Absolute magnitude is the value if the star is set hypothetically to a distance of 10 parsecs. 1 Parsec = 3.3 light years. M= m + 5 + 5logP Distance of stars : Heliocentric parallax for near by ones. Cepheid variables ; Time period of variability related to absolute magnitude. Comparison of absolute to apparent magnitude gives distance.

8. Solar System : Sun, Planets, Satellites, Asteroids, Comets, Meteorites, Gas Nearest Star : Proxima Centauri - 4.3 Light Years MILKY WAY galaxy 200 billion stars , 100,000 ly Sun - 30,000 ly from centre, Period 200 million y Milky way member of local group, 49 galaxies . LMC and SMC, Andromeda 2 Million ly away, 4 times massive

9. Some features of the Solar System Dominant member SUN Oldest - 4.5 Billion years Mass - 99.85% of Solar System Mainly Hydrogen gas, 6000 deg C Photosphere, Chromosphere, Corona Solar wind, Magnetic field Nine planets : Mass 0.135% Jupiter, almost a star. Outer planets, Gas Giants, Hydrogen,Helium, Methane , Ammonia Belts and Rings Inner Planets, terrestrial, Rocky, small Possibility of life Venus , Mercury – effect of tides Slow rotation JUPITER MARS

10. Distance (AU) Radius Mass Rotation # Moons Inclin Ecce ObliqDen Sun 0 109 332,800 25-36 9 1.4 Mercury 0.39 0.38 0.05 58.8 0 7 0.2 0.1 5.43 Venus 0.72 0.95 0.89 244 0 3.394 0.007 177.4 5.25 Earth 1.0 1.00 1.00 1.00 1 0.000 0.0167 23.45 5.52 Mars 1.5 0.53 0.11 1.029 2 1.850 0.0934 25.19 3.95 Jupiter 5.2 11 318 0.411 16 1.308 0.0483 3.12 1.33 Saturn 9.5 9 95 0.428 18 2.488 0.0560 26.73 0.69 Uranus 19.2 4 17 0.748 15 0.774 0.0461 97.36 1.29 Neptune 30.1 4 17 0.802 8 1.774 0.0097 29.56 1.64 Pluto 39.5 0.18 0.002 0.267 1 17.15 0.2482 119.6 2.03

11. Much has been learnt about the solar system thru interplanetary space probes Earlier Appollo series Mariners,Vikings, Pioneers, Voyagers,Galileo ( Venera, Mars) Recently, Rover, Spirit, Opportunity,Cassini Some major features Venus : Surface Temp : 400 deg C. Atmosphere , 95% Carbon-di-oxide, Sulphuric acid. Clouds of frozen CO2 Mars : Polar cap- ice water, Definitely water flowed on the surface once- canyons, Oxygen in the atmosphere. High mountain (Mons Olympus) . Possibility of microscopic life 3 billion years ago. Probably even now Jupitor's moons : Io has active volcano, Europa has water. Jupitor has a belt Saturn's moon - Titan has water and liquid methane Seas Uranus and Neptune have rings . Neptune has lots more satellites

12. Stars : Constellations Magnitude Distance Velocity Spectra, Temp Radius Mass Main Sequence Birth & Death Composition Variable stars Supernova Red Giants White Dwarves Neutron Stars Black holes

13. THANKS FOR BEING PATIENT And giving me a reason for living.