midterm Flashcards
velocity
m/s
acceleration
m/s^2
force
measured in Newtons (kg*m/s2), f = ma
semi major axis
is one half of the major axis, and thus runs from the centre, through a focus, and to the perimeter. Essentially, it is the radius of an orbit at the orbit’s two most distant points. For the special case of a circle, the semi-major axis is the radius.
eccentricity
where a is the semi-major axis, b is the semi-minor axis, and f is the distance from the center of the ellipse to either focus. In this equation, a, b, and f must all have the same units
keeper’s 1st law
The shape of a planet’s orbit is an ellipse with the Sun at one focus, so the distance between a planet and the Sun is not, in general, constant.
newtons 1st
An object at rest will remain at rest unless an unbalanced force acts upon it, and an object in motion will continue moving at the same speed and in the same direction unless an unbalanced force acts upon it
evidence of heliocentrism - retrograde motion
When a planet seems to reverse directions in the night sky
waves
you know
wavelength
(λ) Wavelength is the distance between adjacent peaks of the wave (or, equivalently, between adjacent valleys). It is not the total length of the wave, since a wave may consist of many oscillations, but rather the physical distance between neighboring oscillations in the electric and magnetic fields that make up a light wave. Since wavelength represents a distance per cycle (where “cycle” refers to one complete oscillation of the wave), the complete units of wavelength are meters per cycle (m/cycle). However, the common practice is to omit the “per cycle” portion of these units, so the standard units of wavelength are meters (m).
frequency
(f) Many students struggle to grasp the exact meaning of a wave’s frequency. Your astronomy book probably says something like “Frequency is a measure of the rate at which wave peaks pass a fixed point in space,” and that’s a fine definition. But to develop an intuitive understanding of frequency, just ask yourself how frequently different events happen in your everyday life: how frequently do you eat lunch, or call your mother, or blink? Perhaps once per day, twice per week, and ten times per minute, respectively. Each of these answers is an expression of a frequency, which you can tell by looking at the units. In each of these cases, all units fit the same pattern: number of events per unit time. One lunch/day, two calls/week, and ten blinks/minute all represent the rates at which events occur. Hence frequency always has units of number of events per time, with time usually represented in seconds. In the case of waves (including light), frequency has units of cycles per second, but the term “cycles” is not included explicitly in common practice. This leaves no units in the numerator, making the unit of frequency “per second” or 1/s. This unit is called the hertz (Hz).
doppler effect
an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the redshift seen by astronomers.
PSR 1829
is a pulsar that is approximately 30,000 light-years away in the constellation of Scutum. This pulsar has been the target of interest, because of a mistaken identification of a planet around it. A
the electromagnetic spectrum
kind of radiation including visible light, radio waves, gamma rays, and X-rays, in which electric and magnetic fields vary simultaneously.
light and matter interactions
Remember, light is a manifestation of electromagnetic force. Matter is made up of charged particles due to the nature of atoms, being composed of a positively charged nucleus surrounded by electrons that are in motion. The nuclei in molecules also move with respect to each other.
what is “light” fundamentally?
In astronomy, the word “light” is often used to refer to any type of electromagnetic radiation
kirchoff’s laws
At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node
how does temperature change thermal emission?
absorption is equal to a universal function only of radiative wavelength and temperature.
how does rotation affect absorption lines?
Because of Doppler shifts, faster rotating stars have broader spectral lines.
evidence of heliocentrism - opposition
when the earth is between another planet and the sun
evidence of heliocentrism - mars
fourth planet from the sun and brighter in our eastern night sky
Kepler 2nd law
An imaginary line between a planet and the Sun sweeps out equal areas in equal times, so a planet moves faster when it’s in the portion of its orbit closer to the Sun.
Kepler 3rd law
The square of a planet’s orbital period is proportional to the cube of the semi-major axis of the planet’s orbit, so planets far from the Sun take longer to complete one orbit than planets close to the Sun.
newton’s 2nd
If an unbalanced force (F) acts upon an object of mass (m), the object will experience an acceleration (a) given by a = f/m
