Chapter 2: Patterns in the Sky – Motions of Earth
Jan 02, 2016
Chapter 2:Patterns in the Sky –
Motions of Earth
Looking around the sky:What are the
Constellations?
Every culture has their own constellations
So whose constellations do astronomers use?
88 Official ConstellationsAndromeda
Established by the IAU in 1922 with boundaries finalized in 1928
What you see at night depends on what time it is
If it’s clear, go out tonight sometime and note the locations of the bright stars. Do the same thing two or three hours later to see how things have
moved
What you see at night depends on what month you
look
Looking south in July
Looking south in January
What you see at night depends on where you are
Cerro Tololo Chile
Why does the sky change during the course of a
night?
The Earth rotates about its’ polar axis so the stars make circles around the celestial pole.
Why does the sky change over the course of a year?
As we orbit the Sun, the direction opposite the Sun changes and we only see the stars that are on the
opposite side of Earth from the Sun
Why does the sky change with your location?
As you move away from the pole your horizon moves with you but the locations of the celestial
poles and celestial equator remains the same
The Earth moves in two ways that affect what we see
Orbital motion around the Sun causes seasonal changes in the constellations
Rotational motion around the polar axis causes changes over the course of the night
The Celestial Sphere Model
We know the universe doesn’t rotate around us but it can be useful to imagine that it does
The Celestial Sphere can be used to explain the daily
motions and the changes due to location