Download Observing

Observing
Astronomy 315
Professor Lee Carkner
Lecture 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
Latitude (degrees North of
the Equator)


Longitude (degrees East or
West of the Prime Meridian
running through Greenwich
England)
Navigation

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