Fundamental Motions (PowerPoint)

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Transcript Fundamental Motions (PowerPoint)

Theme 2 – Fundamental Motions
ASTR 101
Prof. Dave Hanes
Information from the Cosmos
Ordinary matter (meteors, cosmic rays, lunar rocks)
Neutrinos (Sudbury Neutrino Observatory!)
Gravitational waves
But principally
Consider Just The Stars First!
Imagine Earth as an isolated rock in space,
unmoving, with no sun or moon.
Looking around, we would see nothing but
the fantastically remote stars, in all
The ‘Fixed’ Stars
like wallpaper
Although stars do move individually, they are so remote
that the patterns don’t change perceptibly for many
thousands of years. But we notice two important features.
Proof: Star Trails
But our location on Earth
makes a difference!
As Seen from the North Pole
(short clips from simulations)
(300x regular speed!)
Looking to the horizon
Looking straight up
Simple Again: From the Equator
Think about Polaris!
As Seen from Near the Equator
(short clips from Stellarium© simulations)
Looking to the Eastern horizon
(from Cali, Columbia)
Looking to the Northern horizon
More Complicated
We live in between (Kingston’s latitude ~ 44o)
Key Things to
The star paths are inclined
The Pole Star stays in an
unchanging location, due North
Some southern stars are never seen by us, while some
Northern stars never go below the northern horizon
(including those in the Big Dipper, for us in Kingston)
Southern stars rise in the Southeast, and follow short paths
across the sky. Northern stars rise in the Northeast, and
follow long paths across the sky
Star Trails from the Northern Hemisphere
Note the Pole Star (nearly unmoving) at the centre of
the pattern.
The Importance of Polaris
1. If lost in the woods at
night, use the Big Dipper
as shown to find Polaris,
which lies due North. This
will help you sort out your
The Importance of Polaris Again
2. If you’re sailing at sea, the altitude of Polaris– how high it is above the
Northern horizon – tells you your latitude. If strong ocean currents carry your
ship North, Polaris will gradually get higher from night to night, and you can
correct your course accordingly; if Polaris gradually gets lower, you are drifting
South. This sort of simple consideration allowed Columbus to sail due west!
What About the Sun??
The Sun is a run-of-the-mill star, but differs in that it is
very close to us! Indeed, we orbit it. As a result (and for
reasons to be explained):
At some times of the year, the Sun behaves like a Southern
star, appearing low in the southern sky
At other times, it is like a Northern star, moving in a much
higher arc through the daytime sky.
That is why we have changing hours of daylight, and why
we experience the seasons – our next topic.