EXAM 2 Flashcards
Newton - what is light?
Light is particles, like bullets or grains of sand
Why are Prue’s glasses pink?
The glasses reflect pink light
Passing light through a prism causes light of a different color to ____ at different angles, creating a rainbow!
refract
Light behaves as a
particle and wave
_____ represents the wavelength of a photon
Color
blue light
400nm
green light
550nm
red light
650nm
light is an ___________ wave
electromagnetic
Speed
the rate at which the peaks of a wave move
Frequency
number of peaks per second that pass by
Speed of light
wavelength × frequency
Do all waves need a medium in which to travel?
Yes
Wiggling a charge creates
electromagnetic radiation: light!
Bluer photons have
higher energy, hotter
What kind of detector would be most efficient for observing a 15,000 K star?
ultraviolet
Why don’t you glow in the dark?
People only emit light with wavelengths our eyes cannot detect
At _____, you generate mostly infrared light that your eyes cannot see
300k
Say you see a feature in a spectrum at
656.3 nm. What are you seeing evidence of?
H (Hydrogen)
Hot, opaque core of star produces the
continuous spectrum
Cool, low-density atmosphere produces the
absorption lines
Is it possible to know if the red supergiant star Betelgeuse has more iron than the Sun?
Yes
How much iron do you think Betelgeuse has
compared to the Sun?
More
What happens to the position of the lines of hydrogen if you heat up a star?
They stay the same
What happens to the position of the lines of hydrogen if the star moves towards you?
They all move to the blue
Doppler Effect
changes the wavelength of a source in motion
51 Pegasi B
“hot Jupiter,” a gas giant planet orbiting very close to its star
What is the minimum amount of time an alien would need to monitor the Sun to find the Earth with the radial-velocity method?
1 year
Biggest doppler shift
smallest distance
Light Curve
derived from a time-lapse movie of how the brightness of an object changes with time
As viewed from Earth, will Venus ever transit in front of the Sun?
Yes
Kepler 10-b
discovered in 2011, was the first confirmed terrestrial (rocky) planet outside our Solar System
Depth =
((radius of the planet)/(radius of the star))^2
Why do astronomers want to look at as many stars as possible with space missions like Kepler or TESS?
Transits need special alignment, so are rare to detect
Kepler
mission aimed at measuring the fraction of Sun-like stars with Earth-like planets.
Kepler 16b
the first circumbinary planet - two sunsets
estimating radius: starquakes
The larger the star’s radius, the longer the period of the pulsations.
estimating radius: luminosity
Amount of energy a star radiates
Apparent Brightness
Amount of starlight that reaches Earth
How would the apparent brightness of Alpha Centauri change if it were the same size but 3 times further away?
1/9 as bright
Stellar parallax
allows us to measure the distance to stars.
How would the parallax of Star B, closer to Earth, compare to the parallax of Star A
Star B has a greater parallax
Luminosity depends only on a star’s
radius and temperature
A star’s intrinsic brightness is sensitive to
T^4
How to measure star’s radius:
1) Measure its distance (parallax) 2) Measure its apparent
brightness to work out ( Count how many photons
we get compared to other stars) its luminosity 3) Measure its temperature (Measure how blue or red the star is)
What do we learn from the transit method?
The planet’s orbital period, the planet’s radius, the planet’s orbital inclination
Would you see transits if i = 0°?
No (orbits on plane so it never is moving towards Earth)
What will happen to the transit if i = 89°?
The shape will always change
Would you detect radial-velocity changes if i = 0°?
No
What do we learn from the Doppler method?
Planet’s orbital period, planet’s eccentricity, planet’s minimum mass
Kepler-10b transits its host star every
20.2 hour
Kepler 10b was detected with the
radial velocity method and transit method
What causes the dips in the Earth’s spectrum?
Molecules
Can we directly take a spectrum of an exoplanet at any given time?
No, need a transit because it is very bright
Visible light
400-700 nm
Light travels through space at a speed that does not exceed
300,000 km/s
Stars much hotter than the Sun give off most light in the
ultraviolet
At 300k
you generate mostly infrared light that your eyes cannot see
Electrons in atoms
are restricted to certain energy levels (quantized)
How electrons in atoms emit photons
An electron is excited to an upper energy level with energy E3. It drops to a lower energy level with energy E2. A photon carries away the difference in energy, E3 – E2
Kepler mission
stared at 150,000 stars for 4 years - transits are rare (we need to see the shadow), so need a big sample.
on average every star has at least 1 planet orbiting <300 days.
Kepler findings
15 ± 13% of Sun-like stars host potentially habitable planets, stars with systems of at least 6 planets, exoplanets orbiting a star at least 10 billion years old, first Tatooine-like planet with two sunsets (orbiting 2 stars)
From transit method, we get ____, from Doppler method, we get ______
radius, mass
Search for molecules like _______ or ______ as biosignatures in exoplanet atmospheres
O2, Methane
