Observing Astronomy 315 Professor Lee Carkner Lecture 3
Dec 19, 2015
Our Point of View
Think about the motions of the heavens from different points of view
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
Caused by the rotation of the Earth on its axis
Caused by the motion of the Earth around the Sun
Observing
Can measure distance on the sky in degrees (360 degrees = complete circle)
Horizon -- Zenith -- Meridian --
Time and the Stars
Stars make one complete circuit around the sky in 24 hours
Example: if stars move 1/12 of the way around the sky, 2 hours have passed
Big Dipper is circumpolar (never sets)
The Seasons
When the northern hemisphere is
pointed at the Sun, it is summer here Seasons are not caused by Earth
being more or less distant from the Sun!!!
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 Day and night
equal in length
Winter Solstice -December Shortest day of the
year
Lines on a Globe Equator -- Sun is overhead at equinox Tropic of Capricorn --
Tropic of Cancer --
Arctic and Antarctic Circles -- 23 1/2 degrees south or north of the pole, Sun never sets or rises at solstice time
Navigation
Latitude (degrees North of the Equator)
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
For observers the ecliptic is a line on the sky where the Sun, Moon and planets can be found
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
For example: March 8th = Pisces, but Sun is in Aquarius. All star signs are about 1 month off
Science and Pseudoscience
Astrology is a pseudoscience, it uses some of the terminology of science, but its basic tenets are not subject to proof