3. Light and spectra Flashcards
What is a wave?
A pattern of motion that can carry energy without carrying matter along with it
What are photons?
Particles of light
Light can act either like a _____ or a _____?
Wave or particle
Each photon has a _____ and a _____
Wavelength and frequency
How does light propagate?
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
What is the electromagnetic spectrum?
EM spectrum is the range of all types of EM radiation
What is Wein’s Law?
Objects of different temperature emit spectra that peak at different wavelengths. It is the relation between peak wavelength and temperature.
What is the Stefan-Boltzmann equation?
What are the 3 basic types of spectra?
Lyman series is in the ultraviolet
Balmer series is in the visible
Paschen series is in the infrared
What is the structure of the atom?
Atoms consist of an extremely small, positively charged nucleus surrounded by a cloud of negatively charge electrons
How is energy stored in atoms?
Absorption of photons
Collisions - transfer of kinetic energy
How does light tell us what things are made of?
Analysis of emission line spectrum, continuous spectrum and absorption line spectrum
How does light tell us the temperature of planets and stars?
Hotter things emit photons of higher energy. The energy of the photon determines its wavelength
How does your eye form an image?
Light hits the retina, photoreceptors turn the light into electrical signal, these travel through the optic nerve to the brain
What are the 2 principal properties of telescopes?
Aperture of the main mirror. The larger the aperture, the more light you can gather
The mount of the telescope
What is the main difference between a telescope and the human eye?
Telescope can gather a lot more light
What is angular resolution? Why is it important?
Angular resolution describes the ability of an image forming device to distinguish small details of an object. Major determinant of image resolution
What is the difference between a reflecting and refracting telescope?
Reflecting uses mirrors
Refracting uses lenses
What are the wavelengths we can observe from the ground?
Infrared, radio, visible
Why is it important to observe astronomical objects at different wavelengths?
More information. We can better understand what’s happening and which processes are important
What are the 3 negative effects the atmosphere has on visible observations?
Absorption
Scattering
Seeing - intensity fluctuations, alter apparent position
What are the 3 basic uses of a telescope?
Light gather, resolving, magnifying
1 degree =
Pi\180 radians
1 arc second =
1/3600 degree. 1 arc minute = 1/60 degree
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?
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.
Gamma rays:
Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?
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
X-rays:
Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?
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
Ultraviolet:
Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?
Wavelength Range (nm): 20–400
Radiated by objects at what temperature: 10^4–10^6 K
Typical sources: Supernova remnants, very hot stars
Visible:
Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?
Wavelength Range (nm): 400–700
Radiated by objects at what temperature: 10^3–10^4 K
Typical sources: Stars
Infrared:
Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?
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
Microwave:
Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?
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
Radio:
Wavelength Range (nm)?
Radiated by objects at what temperature?
Typical sources?
Wavelength Range (nm): More than 10^9
Radiated by objects at what temperature: Less than 10 K
Typical sources: Supernova remnants, pulsars, cold gas
