MORE ANSWERS FROM THE HEAVENS

What can electromagnetic waves tell us about the movement of

planets, stars, and galaxies?

WAVE MOVEMENT 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 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

TYPES OF SHIFTS 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.

EXAMPLES How could redshift, blueshift effect

spectroscopy? What problems can this cause?

QUESTION 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.

THE REST OF THE ELECTROMAGNETIC SPECTRUM 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”.

EXAMPLES What kind of shift would we observe

from Earth for each moving star?

WHAT ABOUT BOTH? 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.

ROTATION

ROTATION

ROTATION

THE SPEED OF LIGHT 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.

QUESTIONS 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!

OUR UNIVERSE 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?

NOT SO FAST SAID EDWIN HUBBLE Edwin Hubble was an American

astronomer in the 20th 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

RATE OF THE EXPANDING UNIVERSE 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?

WHY IS THE UNIVERSE EXPANDING AT AN INCREASING RATE? 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.

EVIDENCE OF DARK ENERGY 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

WELL THEN WHERE IS IT? 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.

TEST IN TWO DAYS Tomorrow we will review What you need to know:

What is the electromagnetic spectrum?Properties of lightWave-Particle duality of lightEnergy of lightSpectroscopyEnergy Levels and Energy Level TransitionsFind temperature of starsDoppler Effect and the electromagnetic

spectrum