Observing and the Sky Astronomy 311 Professor Lee Carkner Lecture 3
Our Point of View We are all standing on different parts of a large spinning ball moving through space Remember that everything is moving at once
The Changing Sky North Pole of the Earth is pointed at Polaris (the North or Pole star), which stays stationary as the other stars move around it Sky makes one complete rotation per 24 hours (Diurnal motion) Sky also makes one complete rotation per year (Annual motion)
Diurnal Motion
Annual Motion
The Observer’s View
Observing Can measure distance on the sky in degrees (360 degrees = complete circle) Horizon -- Zenith -- Meridian --
The Solar Year
The Seasons Tilt of Earth’s axis causes seasons Sunlight is more direct in the summer
Direct and Indirect Sunlight
Solstice and Equinox Solstice When the Sun is highest or lowest in the sky Equinox When the Sun is overhead at the equator
Times of year Vernal Equinox -- March First day of spring Summer Solstice -- June First day of summer Autumnal Equinox - -September First day of autumn Winter Solstice - December First day of winter
Changing Day Length
Lines on a Globe Equator -- Sun is overhead at equinox Tropic of Capricorn -- Tropic of Cancer -- Arctic and Antarctic Circles /2 degrees south or north of the pole, Sun never sets or rises at solstice time
Navigation Latitude (degrees North of the Equator) Only works in Northern hemisphere Longitude (degrees East or West of the Prime Meridian running through Greenwich England)
The Celestial Sphere Project the lines on a globe into space to form a coordinate system North Celestial Pole – Celestial Equator --
Celestial Coordinates Right Ascension -- Declination -- The coordinates do not move or vary with location on the Earth, they are fixed to the stars
The Ecliptic Most of the objects in the solar system have their orbits in the same plane, called the ecliptic The ecliptic passes through 12 constellations known as the zodiac
Constellations of the Zodiac
Precession The Earth “wobbles” as it spins, causing the Earth’s axis to point at different parts of the sky This changes where the equinoxes are in the sky
Astrology The belief that the positions of heavenly bodies at the time of your birth foretells your future Your sign is where the Sun was on the zodiac when you were born For example: Sept 13th = Virgo, but Sun is in Leo. All star signs are about 1 month off
Science and Pseudoscience Astronomy is a science, it tries to form a picture of the universe based on observation and reason. It is subject to proof
Next Time Meet back in Science 102 Read Chapter 1.6