3. Light and spectra

Question 1

What is a wave?

Answer 1

A pattern of motion that can carry energy without carrying matter along with it

Question 2

What are photons?

Answer 2

Particles of light

Question 3

Light can act either like a _____ or a _____?

Answer 3

Wave or particle

Question 4

Each photon has a _____ and a _____

Answer 4

Wavelength and frequency

Question 5

How does light propagate?

Answer 5

Inverse square law. Since the area increases as the square of the distance, the brightness of the light decreases as the inverse square of the distance

Intensity= 1/D^2

Question 6

What is the electromagnetic spectrum?

Answer 6

EM spectrum is the range of all types of EM radiation

Question 7

What is Wein’s Law?

Answer 7

Objects of different temperature emit spectra that peak at different wavelengths. It is the relation between peak wavelength and temperature.

Question 8

What is the Stefan-Boltzmann equation?

Answer 8

Question 9

What are the 3 basic types of spectra?

Answer 9

Lyman series is in the ultraviolet

Balmer series is in the visible

Paschen series is in the infrared

Question 10

What is the structure of the atom?

Answer 10

Atoms consist of an extremely small, positively charged nucleus surrounded by a cloud of negatively charge electrons

Question 11

How is energy stored in atoms?

Answer 11

Absorption of photons

Collisions - transfer of kinetic energy

Question 12

How does light tell us what things are made of?

Answer 12

Analysis of emission line spectrum, continuous spectrum and absorption line spectrum

Question 13

How does light tell us the temperature of planets and stars?

Answer 13

Hotter things emit photons of higher energy. The energy of the photon determines its wavelength

Question 14

How does your eye form an image?

Answer 14

Light hits the retina, photoreceptors turn the light into electrical signal, these travel through the optic nerve to the brain

Question 15

What are the 2 principal properties of telescopes?

Answer 15

Aperture of the main mirror. The larger the aperture, the more light you can gather

The mount of the telescope

Question 16

What is the main difference between a telescope and the human eye?

Answer 16

Telescope can gather a lot more light

Question 17

What is angular resolution? Why is it important?

Answer 17

Angular resolution describes the ability of an image forming device to distinguish small details of an object. Major determinant of image resolution

Question 18

What is the difference between a reflecting and refracting telescope?

Answer 18

Reflecting uses mirrors

Refracting uses lenses

Question 19

What are the wavelengths we can observe from the ground?

Answer 19

Infrared, radio, visible

Question 20

Why is it important to observe astronomical objects at different wavelengths?

Answer 20

More information. We can better understand what’s happening and which processes are important

Question 21

What are the 3 negative effects the atmosphere has on visible observations?

Answer 21

Absorption

Scattering

Seeing - intensity fluctuations, alter apparent position

Question 22

What are the 3 basic uses of a telescope?

Answer 22

Light gather, resolving, magnifying

Question 23

1 degree =

Answer 23

Pi\180 radians

Question 24

1 arc second =

Answer 24

1/3600 degree. 1 arc minute = 1/60 degree

Question 25

Suppose the surface temperature of the Sun were about 18,000 K, rather than 6,000 K. How much more thermal radiation would the Sun emit?

Answer 25

From the first rule of thermal radiation, we know that tripling the temperature of an
object increases the amount of thermal radiation it emits per unit area by a factor of 3^4 = 81.
Thus, increasing the surface temperature of the Sun from 6,000 K to 18,000 K would increase its thermal radiation by a factor of 81.

Question 26

Gamma rays:

Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?

Answer 26

Wavelength Range (nm): Less than 0.01

Radiated by objects at what temperature: More than 10^8 K

Typical sources: Produced in nuclear reactions; require very high-energy processes

Question 27

X-rays:

Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?

Answer 27

Wavelength Range (nm): 0.01–20

Radiated by objects at what temperature: 10^6–10^8 K

Typical sources: Gas in clusters of galaxies, supernova remnants, solar corona

Question 28

Ultraviolet:

Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?

Answer 28

Wavelength Range (nm): 20–400

Radiated by objects at what temperature: 10^4–10^6 K

Typical sources: Supernova remnants, very hot stars

Question 29

Visible:

Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?

Answer 29

Wavelength Range (nm): 400–700

Radiated by objects at what temperature: 10^3–10^4 K

Typical sources: Stars

Question 30

Infrared:

Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?

Answer 30

Wavelength Range (nm): 10^3–10^6

Radiated by objects at what temperature: 10–10^3 K

Typical sources: Cool clouds of dust and gas, planets, moons

Question 31

Microwave:

Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?

Answer 31

Wavelength Range (nm): 10^6–10^9

Radiated by objects at what temperature: Less than 10 K

Typical sources: Active galaxies, pulsars, cosmic background radiation

Question 32

Radio:

Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?

Answer 32

Wavelength Range (nm): More than 10^9

Radiated by objects at what temperature: Less than 10 K

Typical sources: Supernova remnants, pulsars, cold gas