Big Questions If astronomers measure an object’s apparent brightness (flux), what do they need to know to figure out how far away that object is? Why are astronomers interested in different parts of the electromagnetic spectrum? How do an object’s size and temperature affect the light it emits, both the quantity and the color? How can astronomers take a star’s temperature from so far away?

Below are four Honda Civics driving toward you at sunset with their headlights turned on. Each car is equipped with identical headlights. Rank the distance that each car is from you from greatest to least.

Below are four Honda Civics driving toward you at sunset with their headlights turned on. Each car is equipped with identical headlights. Rank the apparent brightness (flux) of each car’s headlights from greatest to least.

Below are four Honda Civics driving toward you at sunset with their headlights turned on. Each car is equipped with identical headlights. Rank the absolute brightness (luminosity) of each car’s headlights from greatest to least.

The figure below shows five stars (A-E) as they appear in the night sky from Earth. A darker shade is used to indicate the appearance of a dimmer star. The distances to each star are unknown. Rank the flux of each star from greatest to least. 1 2 3 5 4

The figure below shows five stars (A-E) as they appear in the night sky from Earth. A darker shade is used to indicate the appearance of a dimmer star. The distances to each star are unknown. Rank the luminosity of each star from greatest to least. 1 2 3 5 4

Visible Rusty

Infrared Rusty

USA - Visible

USA - IR

USA - gamma

USA - radio

The Whirlpool Galaxy, M51 Infrared: warm dust Radio: cold gas & magnetic fields Visible: stars Ultraviolet: young stars X-ray: black holes and neutron stars

 Atomic H gas GMCs dust  Forming stars  Stars  Hot gas & binaries  Cosmic rays colliding with the interstellar meduim

energy than ultraviolet light Infrared light has 1-greater 2-less energy than ultraviolet light

wavelengths than gamma ray photons X-ray photons have 1-longer 2-shorter wavelengths than gamma ray photons

Visible electromagnetic radiation has a 1-higher 2-lower frequency than radio wave electromagnetic radiation

speed than microwave light Infrared light has a 1-faster 2-slower speed than microwave light

Of all the types of light the sun gives off, it emits the greatest amount of light at visible light wavelengths. If the sun were to cool off dramatically and as a result start giving off mainly light at wavelengths longer than visible light, how would the frequency, energy and speed of this light given off by the sun also be different? Frequency : Energy: Speed:

Emits most light ___ ___ ___ ___ ___ Emits least light A B C D E The hot plates are shaded according to temperature (darker shading means colder). Rank the hotplates in order by how much light they emit. Emits most light ___ ___ ___ ___ ___ Emits least light

Below is the information about several stars Below is the information about several stars. Rank the stars in order by the total amount of light they emit. Star Radius [Rsun] Temperature [K] Distance [lyr] alpha 1 4,000 25 beta 2,000 78 gamma 2 8,000 13 delta 4 16,000 104 epsilon 57 Emits most light ___ ___ ___ ___ ___ Emits least light

Color  Temperature! Which stars are hottest? Which stars are hottest? Coolest? Which stars are hottest? Color  Temperature!

The figure below is a graph of luminosity and temperature. Which group of stars is the red giants? 1 2 3 4

The figure below is a graph of luminosity and temperature. Which group of stars is the white dwarfs? 1 2 3 4

The figure below is a graph of luminosity and temperature. Which group of stars is the red dwarfs? 1 2 3 4

Flux Blue Red Wavelength (nm)

Which star is the hottest?

What color is Star 2? (The visible part of the spectrum goes from 4000 to 7000 on this scale). Star 1 Star 3 Star 2

Big Questions How does light interact with matter? How does quantum mechanics affect these interactions? How do the spectra of opaque and non-opaque objects differ? When do astronomers observe absorption lines vs emission lines? What information can astronomers learn directly from the spectrum of an object?

Questions about Emission and Absorption: The picture to the right is of the Ring Nebula -- a bubble of gas surrounding a small star. If you aimed the Hubble Space Telescope at box A and took a spectrum, what would you expect to see? 1- Emission lines 2- Absorption lines 3- Blackbody continuum 4- None of the above A B

Questions about Emission and Absorption: The picture to the right is of the Ring Nebula -- a bubble of gas surrounding a small star. If you aimed the Hubble at box B and took a spectrum what would you expect to see? (Note - box B contains a star) 1- Emission lines 2- Absorption lines 3- Blackbody continuum 4- None of the above A B

Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by reflected sunlight? 1 2 3 4 5

Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by hot carbon dioxide gas in the upper atmosphere of Mars? 1 2 3 4 5

Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by Mars’ own blackbody radiation? 1 2 3 4 5

Below is the spectrum for the planet Mars from UV to IR. What color does Mars appear? 1 2 3 4 5

Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by absorption by the red soil of Mars? 1 2 3 4 5

The visible light emitted by hydrogen is caused by transitions from higher energy levels down to the 1st excited state. Below is the emission spectrum of hydrogen gas. Draw an atom, including a nucleus and five energy levels. Using a dot to represent the electron and an arrow to represent its motion, sketch and label what happens to the electron to create the red emission line. On the same drawing, sketch what happens to the electron to create the blue emission line.