Flashcards
2022-02-08
Where does the definition for $1 \text{au}$ come from??
The average earth-to-sun distance.
What does the definition for $1 \text{ly}$ come from??
It’s the speed light travels per year in a vacuum.
What’s “parsec” short for??
“parallax arcsecond”
What is $1$ degree in arcminutes (READ)??
$$ 60 \text{arcminutes} $$
What is $1$ arcminutes in arcseconds (READ)??
$$ 60 \text{arcseconds} $$
What is $1$ degree in arcseconds (READ)??
$$ 3600 \text{arcseconds} $$
What is the notation for one arcminute??
$$ 1' $$
What is the notation for one arcsecond??
$$ 1'' $$
What is the formula for distance in parsecs??
$$ \text{distance in parsecs} = 1/\text{distance in arcseconds} $$
What is the formal definition of a parsec??
The distance at which a $1\text{au}$ base line subtends an angle of $1$ arcsecond.
How can you work out the numerical value of $1 \text{pc}$ (parsec)??
$$ 1\text{pc} = \frac{1 \text{au}}{\tan(1/3600)} $$
What is the Doppler effect??
The relative change in frequency/wavelength of a wave when there is a relative velocity between observer and source.
What is true about the relationship between relative velocity and change in wavelength in the Doppler effect??
$$ \text{relative velocity} \propto \text{change in wavelength} $$
What happens to frequencies in red shift??
They decrease.
What happens to wavelengths in red shift??
They increase.
Is a red shifted source moving away or towards you??
Away from you.
In red shift, what happens as the source is moving away from you??
The waves are spreading out.
What happens to frequencies in blue shift??
They increase.
What happens to wavelengths in blue shift??
They decrease.
Is a blue shifted source moving away or towards you??
Towards you.
In blue shift, what happens as the source is moving towards you??
The waves get bunched together.
What is the Doppler equation in terms of change in wavelength $\Delta \lambda$, original wavelength $\lambda$, velocity $v$ and the speed of light $c$??
$$ \frac{\Delta \lambda}{\lambda} \approx \frac{v}{c} $$
What is the Doppler equation in terms of change in frequency $\Delta f$, original frequency $f$, velocity $v$ and the speed of light $c$??
$$ \frac{\Delta f}{f} \approx \frac{v}{c} $$
What is the condition for using the Doppler equation??
$$ v « c $$
How would you know the original wavelength when using the Doppler equation??
You’d measure the emission or absorptions lines of a source in a lab.
What is the rough limit of measurement due to stellar parallax??
$$ 100 \text{pc} $$
2022-02-11
What is Hubble’s law in terms of direct proportionality??
$$ \text{recessional velocity of a galaxy} \propto \text{distance of a galaxy} $$
Because of Hubble’s law, what is generally true the further away a galaxy is??
It’s moving faster.
What is Hubble’s law in equation form, in terms of $v$, $d$ and $H_0$??
$$ v = H_0 d $$
How can Hubble’s law work if galaxies like Andromeda are moving towards us??
Because it is applied to the whole universe on average, not on a case-by-case basis.
How can you work out the age of the universe given Hubble’s constant $H_0$??
$$ 1/H_0 $$
What is the approximate value of Hubble’s constant in $\text{km s}^{-1}\text{Mpc}^{-1}$??
$$ \text{km s}^{-1}\text{Mpc}^{-1} $$
What is the cosmological principle??
The assumption that the universe is isotropic and homogenous.
What are the two assumptions made about the universe in the cosmological principle??
- Isotropic
- Homogenous
What does “the universe is isotropic” mean??
It looks the same in all directions.
What does “the universe is homogenous” mean??
Matter is uniformly distributed across the universe.
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date: 2022-02-08 18:47
tags:
- '@?public'
- '@?school'
- '@?physics'
- '@?year-2'
- '@?cosmology'
title: Physics - Cosmology