Observational Astronomy

Astronomy from space Hubble Space Telescope

Atomic Energy Theory of Relativity

Nebulae – stellar nurseries

Spiral Galaxy and Nucleus

Hubble Deep Field: 10,000 Galaxies

Universe: Past and Present

Cosmic Epochs and Evolution

Relative Sizes in astronomy From very small to very large (meters)

Some Essential Numerical Figures Radius of the Earth = 6500 Km Speed of light – 300,000 Km/sec Astronomical distances are so large that we use the speed of light to measure them Mean Earth-Sun Distance – 150 million Km = 1 Astronomical Unit (AU) = 8.3 Light Minutes 1 Light Year (Ly) = 9.5 trillion Km = 63,240 AU Parsec = 3.26 Lys (parallax angle unit)

The Milky Way 100,000 Lys Across

Stellar Constellations Connect bright stars to discern some shape

Ancient Figures and Constellations

The Orion Constellation

The North Star (Polaris)

The Summer Triangle

Winter Triangle of Bright Stars

The Distance Scale

LINEAR AND ANGULAR SIZE OF OBJECTS   angle subtended by the object at the observer; the farther the object, smaller the 

Angular size of moon = 30’ 1 Degree = 60’ (minutes) = 60 x 60 = 3,600 ‘’ (seconds) What is the angular size of the Sun? How large does the Sun appear ?

Angular ‘distance’ between stars While angular distance can be measured by observations, actual distances are difficult to measure (What do we need?)

Orbital and angular motion of the Earth The Earth moves one degree in its orbit around the Sun each day. Why?

Parallax: Measurement of Distance Apparent movement due to viewing position No actual motion of the viewed object Difference in angle between line of sight from the Earth and from the Sun (half the diameter or the radius of the Earth’s orbit, 1AU) Since the parallax of stars is very small, it is measured in parsec (parallax second) distance d= 1/p OR p = 1/d 1 parsec = 3.26 LY = 206,265 AU

Distance Measure in Astronomy: The Parallax Method 1 parsec (pc) = 3.26 Light Years (Ly) Circle = 360 o (degrees) 1 degree = 60’ (minutes) 1 minute’ = 60” (arcseconds) Measure of distances in angles: The distance d of an object that makes an angle of 1” as the Earth moves to opposite sides of the Sun d Object at a distance of 1 pc d (pc) = 1 /  Parallax is the change in angle due to motion   90 1 AU d

Stellar and Astronomical Distances 1 parsec (pc) = 3.26 LY = 205,000 AU The stars are very far away Nearest Star Alpha Centauri  4.3 LY, more than 1 pc ! The parallax angle  is less than one arcsecond (“) That’s why the Greeks could not see the stars move Galaxies have been seen up to more than 10 billion Lys away

Night Sky Exposure Geocentric or Heliocentric ?

Earth’s rotation and the Sky

Daily Rotation of the Earth and Stars

Annual Revolution of the Earth around the Sun and position of stars

Location of Heavenly Objects How do you locate places on the Earth? Latitude and Longitude Latitude: angle measured from the Equator (0 o ), up or down, N-S Longitude: angle measured from the Prime Meridian, E-W, 0 o – 180 o How would you find location in mid-ocean ? First rule of navigation: Lookup angle of Polaris  Latitude How do you find the longitude? Clock ?

Celestial Map and Celestial Coordinates Celestial Poles And Equator – Extension of the Earth’s poles And equator Celestial Equator is the extension of the Earth’s Equator up to the CS Analogous to Latitude and Longitude on The Earth – Measured in Degrees

Ecliptic and the Celestial Equator The Ecliptic and the Celestial Equator Intersect at Vernal (Spring) and Autumn Equinoxes At an angle of 23.5 o to each other Ecliptic is the apparent Path of the Sun on the Celestial Sphere Autumn Equinox Vernal Equinox Winter Solstice Summer Solstice

THE CELESTIAL SPHERE: Coordinates and Map of Objects in the Sky Declination  “celestial latitude” Right Ascension  : “celestial longitude” Vernal Equinox: Position of Sun In the Sky on the first day of spring; Day = Night  = 0 Star at (  “celestial coordinates” Star

Apparent Rotation of Celestial Sphere