Astronomy Quiz 1 Flashcards
What is dark matter and how do we know it exists?
It is “dark” matter because it doesn’t emit a physical light, we know it exists b/c of the gravitational attraction of matter around it
What is a photon? How is a photon created?
A photon is the mediator of the electromagnetic force. An electron is stimulated and jumps/ transitions to an outer orbital thus using energy, they need to get back to a lower energy so they release energy in the form of a photon
What is the observable universe?
the distance that light has traveled since the universe was born - the universe is expanding and as it expands there’s more distance the light has to travel - size of the observable universe is larger than the speed of light x time
What is causing the light in the northern lights?
Charged particles from the sun get caught in the field lines of the magnetic field. Then they hit other particles in the atmosphere, causing an electron inside the atom to be excited to a higher state, the electron then needs to get back to equilibrium so it falls back to a de-excited state and emits a photon to help shed excess energy
How is the color of the northern lights determined?
molecular structure of the atmosphere, the chemicals in the atmosphere
- the number of electrons and the sets of energy levels are different in every element, so nitrogen and helium give off different colors
- the electrons absorb certain wavelengths of light?
Light - energy and color range
lowest - red
middle: orange, yellow, green, blue, indigo
highest - violet
How do we get a picture?
red, blue, green photons - we put them together into pixels
What is a spectroscopy?
take photons and split into wavelengths thru a spectrograph
example: Prism
Prism takes light coming in, splits it up by it’s individual wavelength - in each wavelength you can count the photons
How do we use a spectroscopy to measure the chemical composition of an object?
Each element absorbs light at specific wavelengths unique to that atom. When astronomers look at an object’s spectrum they can determine its composition based on these wavelengths
You take the photons of an object, and look at the individual wavelengths thru a spectroscopy
Using wavelength to inform you what the elements are of that source - if you see wavelengths that correspond to hydrogen or helium then you know
periodic table is encoded in the transition points
Thought experiment 1: Time is relative in a moving frame
Imagine we’re in a box, and professor has a laser pointer pointed at a mirror on the ceiling - say we record how long it takes for laser to hit mirror and reflect back down
Thought experiment 2: ship
Say we are in a ship inside the same box and the ship is moving with velocity. Say we put a mirror on the top of the ceiling and shine the laser on it as well.
What does someone see from the outside?
They see light going up but when it comes back down it comes back down in a different spot
you have moved with the ship but you don’t know you’re moving
Speed of light
speed of light is constant in any reference frame
no matter how fast someone is running at you with a flashlight = the speed of light will always be the same
if we calculated the velocity of the person running + the speed of light it would change the physics of the universe
Thought experiment 1 vs 2
d2 > d1 and t2>t1
distance of the second laser is greater than the distance of the first one therefore the time of the second laser is greater than the first
Thought experiment 3
Rocket ship is accelerating and increasing velocity every second
if we connect the laser pointer to the heartbeat of person A (on the bottom near the propellers) and send pulse light to person B - the light has to travel more distance each pulse - each pulse of light takes a little bit longer
If person B on the top sends a pulse light down to person A it will seem like their heart is beating faster because there’s less distance to travel for the pulse due to the acceleration
