What can electromagnetic waves tell us about the movement of planets, stars, and galaxies?

 What happens when an object is emitting a constant frequency sound wave as it moves towards you?  What happens when an object is emitting a constant frequency sound wave as it moves away from you?  What was this called?

 The Doppler effect effects electromagnetic waves just like it effects sound waves.  We cannot hear electromagnetic waves, so we detect the wavelength shift with our eyes

 Blueshift – If an object is moving towards us, its light is shifted to shorter wavelengths. Shorter wavelengths of visible light are bluer.  Redshift – If an object is moving away from us, its light is shifted to longer wavelengths. Longer wavelengths of visible light are redder.

 How could redshift, blueshift effect spectroscopy?  What problems can this cause?

 If we are constantly reflecting light, why don’t we observe either a blueshift or a redshift when we move?  The speed of light is so much faster than any movement we make so the Doppler Effect is negligible.

 What kinds of shifts do we have for the rest of the electromagnetic spectrum?  To keep everything simple we only use the terms, “blueshift” and “redshift”.

 What kind of shift would we observe from Earth for each moving star?

 Is it possible for a star or galaxy to have both a blueshift and a redshift?  Yes, if it is rotating!  We can tell if a star or galaxy is rotating or not by looking for a blueshift on one side and then a redshift on the other.  We can also calculate the rotation speed of the object.

 Does the speed of the electromagnetic wave change during a Doppler shift? Why or why not?  Similar to how sound waves cannot travel faster than the speed of sound, electromagnetic waves cannot travel faster than the speed of light.

 If a dust cloud is emitting infrared light as it is traveling toward Earth is it plausible for us to see it with our un-aided eye?  Yes!  If a dust cloud is emitting ultraviolet light as it is traveling toward Earth is it plausible for us to see it with our un-aided eye?  No!

 What is the Big Bang Theory  Not the TV show  After the Big Bang the universe has nothing left to keep making it expand right?  So eventually gravity will pull everything back together and we will have another Big Bang right?

 Edwin Hubble was an American astronomer in the 20 th century who observed that distant galaxies have redshifts.  He was able to show that the recessional velocity of a galaxy increases with its distance from Earth, implying the universe is expanding.  Hubble’s Law

 So it is still possible that the universe is expanding at a decreasing rate so maybe one day gravity will win and we will have a second big bang right?  Nope, in 1998 observations were made that suggested that the expansion of the universe has been accelerating.  Why?

 We don’t know.  Most believe it is because of Dark Energy!  Dark Energy: A hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe.

 In the current Standard Model of Cosmology (which explains where everything ever came from) the universe contains:  26.8% Dark Matter  68.3% Dark Energy  4.9% Ordinary Matter

 We believe that dark energy is scattered evenly throughout the whole entire universe, even on Earth.  There is not enough dark energy or dark matter on Earth for it to be noticed by us, or mess up anything.  We’ve estimated that we would find just 6 tons of dark energy within the radius of Pluto’s orbit.  However, it comes to dominate the mass-energy of the universe because it is uniform across space.

 Tomorrow we will review  What you need to know:  What is the electromagnetic spectrum?  Properties of light  Wave-Particle duality of light  Energy of light  Spectroscopy  Energy Levels and Energy Level Transitions  Find temperature of stars  Doppler Effect and the electromagnetic spectrum