3observing3s
Download
Report
Transcript 3observing3s
Observing and the Sky
Astronomy 311
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
Sky makes one complete rotation per
24 hours (Diurnal motion)
Sky also makes one complete rotation
per year (Annual motion)
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 -- line running from north to
south through zenith
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
Equinox
When the Sun is
highest or lowest in
the sky
When the Sun is
overhead at the
equator
Longest or shortest
day of year
Day and night equal
in length
Changing Day Length
Lines on a Globe
Equator -Tropic of Capricorn -- 23 1/2 degrees
south of the equator, Sun overhead on
Winter solstice
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
Equal to the angle of Polaris
above horizon
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 -Project the Earth’s
equator into space
Celestial Coordinates
Right Ascension -- degrees east from where
the sun is on the Vernal Equinox (first day of
spring)
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
Your sign is supposed to be where the
Sun was on the zodiac when you were
born
For example: Sept 10th = 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
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 on Monday
Read Chapter 1.6