Theme 2 – Fundamental Motions ASTR 101 Prof. Dave Hanes

Information from the Cosmos Ordinary matter (meteors, cosmic rays, lunar rocks) Ordinary matter (meteors, cosmic rays, lunar rocks) Neutrinos (Sudbury Neutrino Observatory!) Neutrinos (Sudbury Neutrino Observatory!) Gravitational waves Gravitational waves But principally LIGHT! But principally LIGHT!

Conspicuous Objects

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 directions.

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 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 Looking to the Northern horizon

More Complicated We live in between (Kingston’s latitude ~ 44 o )

Key Things to Notice The star paths are inclined The star paths are inclined The Pole Star stays in an The Pole Star stays in an unchanging location, due North 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) 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 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 directions.

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 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. 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.