Observing

Astronomy 315Professor Lee

CarknerLecture 3

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

Diurnal Motion

Annual Motion

The Observer’s View

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 Solar Year

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!!!

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 Day and night

equal in length

Winter Solstice -December Shortest day of the

year

Changing Day Length

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

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

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

Next Time

Meet back in Science 102 Read Chapter 3.1-3.4