Early Astronomy
Stars are approximately these kinds of objects and a relationship between surface temperature and peak wavelength emitted is given by this law.
What are blackbodies and Wein's Law?
According to Hubble's law, this is the observed effect of galaxies as we look further out.
What is the velocities away from us are greater with larger distance?
Say that starlight passes through a cloud of hydrogen on the way to us. How can we see that hydrogen was present?
There will be absorption lines in the spectrum of the light corresponding to electron jumps in hydrogen.
This is the effect that has caused Venus to become extremely hot.
What is the greenhouse effect?
This is the mechanism by which retrograde motion operates in the Copernican system.
What is differential motion of the Earth and planet?
Say there is a star that we observe to be moving tangentially to us. What can we say about its velocity via the Doppler method?
We can't get an estimate for its velocity as the Doppler shift only occurs for radial motion. We CAN still determine what elements are present though.
This is the best solution to Olber's paradox.
What is the Universe has a finite age? This means there hasn't been enough time for starlight to reach us to completely brighten the sky.
How might we detect a black hole without being able to actually see it?
See how stars or other objects we can see behave around a point in space and deduce via Newton's laws that a mass is there.
Gravitational waves
This is the main way we know how old the Solar System is.
What is radioactive dating of Moon rocks? (gives about 4.6 billion years)
Explain how objects orbit according to Newton.
Gravity (defined by equation) pulls the object towards the large mass, but the tangential motion of the object causes it to want to fling outward; centrifugal motion.
How do main sequence stars evolve on the HR diagram?
They move to the right off the diagonal of the MS and most become red giants in the top right.
This is the earliest light that we can see in the Universe, and also gives estimates for the flatness of the Universe as well as a value for Hubble's constant.
What is the Cosmic Microwave Background?
It is thought that the flat rotation curves of galaxies are caused by this, and makes up about 25% of the composition of the Universe.
Explain why we can see total solar eclipses from Earth.
The angular sizes of the Moon to the Sun on the sky perfectly match their distances to us so that the Moon can fully cover the Sun.
These are a few observations of Galileo that proved the Copernican model.
What are the moons of Jupiter, craters on the Moon, phases of Venus, etc.?
Describe the approximate path that the Sun will take after the main sequence.
After nuclear fusion of hydrogen to helium is finished in the core, the Sun will transform to a Red Giant to a planetary nebula to a white dwarf.
This is the best theory that answers the horizon and flatness problems, as well as estimates the actual size of the Universe to be much much larger than what we can see.
What is inflation? (See course reader for more details)
These explosions occur when a white dwarf exceeds the Chandrasekhar limit. They are also used for measuring distances and hence are called these.
What are Type 1A SN and standard candles?
(Type 2 come from core-collapse of massive stars)
Say aliens are looking at our star the Sun through telescopes. What are 2 methods for which they could detect planets orbiting the Sun?
Doppler wobble: measure the Doppler shift as Sun wobbles
Transit: measure periodic dips in brightness caused by an orbiting planet
Telescopes were used in the early days to collect more light. For a telescope that has a 6-meter diameter, how much more light can it collect compared to the human pupil of 6 milimeters?
(6000mm/6mm)^2 = (1000)^2 = 10^6
Suppose you observe a binary star system. You measure a flux from star A to be 2000 and the flux from star B to be 2. What is the relative luminosity of A to B?
At the same distance in a binary system, so the only terms that matter are flux and luminosity.
F_A/F_B = L_A/L_B L_A/L_B = 1000
Could solve for radius or temperature given knowledge of either of those parameters.
Let's say that the Universe only had dark energy so that expansion has been constantly accelerating. Would the predicted age of the Universe be older or younger than that of a flat universe?
Older, the expansion has to "catch up" to the flat expansion much like an accelerating car must start farther to meet a cst. velocity car at the same point.
These objects produce massive amounts of radiation from a small volume in a galaxy and are thought to be due to accretion from supermassive black holes. What about them baffled astronomers?
What are quasars? Their high redshift implied that the luminosity of the quasar was staggering given the flux we receive on Earth.
Describe several reasons why Pluto was demoted from being a planet.
Not massive enough to clear local area with gravity; eccentric and inclined orbit; deviant density; many other objects that are similar in Kuiper Belt