Intro To Astronomy

Question 1

Central meridian (zero point for measuring positions in sky)

Answer 1

Vernal equinox

Question 2

Right ascension (RA)

Answer 2

Longitude (expressed as hour angle)

Question 3

Declination (δ)

Answer 3

Latitude (expressed as an angle)

Question 4

Synodic day

Answer 4

Solar day, time for earth to make one full rotation around the sun (24:00)

Question 5

Sidereal day

Answer 5

Time for earth to be at the same point relative to the sun from the point of view of an earth observer (23:56:04)

Question 6

Length of year (SI days)

Answer 6

365.2422 SI days

Question 7

1 AU

Answer 7

Distance from Earth to the Sun (1.5 x10^11m)

Question 8

Parsec

Answer 8

Distance corresponding to a parallax angle of 1” (3.086 x10^16m)

Question 9

Parallax

Answer 9

Apparent motion of stars due to the Earth’s orbit around the Sun, movement by an angle 1AU/d(pc)

Question 10

Proper motion

Answer 10

The transverse component of a star’s drift (i.e. motion in space)

Question 11

Flux

Answer 11

Received light power per unit area (W/m^2)

Question 12

Apparent brightness

Answer 12

Received light power (W)

Question 13

Luminosity

Answer 13

Total energy-rate (power) emitted (W)

Question 14

Absolute magnitude

Answer 14

The apparent magnitude we would observe if the object was 10pc away

Question 15

Visible window of wavelengths and frequencies

Answer 15

λ = 400-700nm,
f = 4-8 10^14 Hz

Question 16

Black body emission

Answer 16

• Looks like a poisson curve
• T increases ⇒ BBR increases at all wavelengths
• T increases ⇒ peak at shorter wavelength

Question 17

Planet

Answer 17

A celestial body that

a) is in orbit around the Sun,
b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
c) has cleared the neighbourhood around its orbit

Question 18

Dwarf planet

Answer 18

A celestial body that

a) is in orbit around the Sun,
b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
c) has not cleared the neighbourhood around its orbit,
d) is not a satellite

Question 19

μ

Answer 19

Mean mass per particle

Question 20

Open cluster

Answer 20

Groups of a few 100-1000 stars, <10 pc across

These clusters a wide range of ages

Question 21

Globular clusters

Answer 21

10^5-10^6 stars in a spherical cluster, 20-50 pc across

All very old, ~10^10 years

Question 22

Mass-luminosity relation

Answer 22

L ∝ M⁴

Question 23

Importance of clusters for stellar evolution

Answer 23

• same distance from earth
• have formed from a gas with the same composition
• same age

Question 24

Chansrakhar limit

Answer 24

Maximum mass of a white dwarf due to relativistic limit

M_Ch = 1.33M☉

Question 25

Cepheid variable stars

Answer 25

Giants that show regular pulsations, whose pulsation period only depends on the absolute magnitude of the star.
Hence measuring this period and apparent magnitude gives distance

Question 26

Doppler shift of galaxy light

Answer 26

λ’ = λ₀(1+v/c)

Where λ’ is observed, λ₀ is rest wavelength

Question 27

Redshift z

Answer 27

z = (λ’ - λ₀)/λ₀ = v/c

Question 28

Cosmic Microwave Background

Answer 28

Peaks at λ ~ 1mm and T = 2.7K

Question 29

Kepler’s Third Law

Answer 29

When m<

Question 29

Hydrostatic equilibrium

Answer 29

dP/dR = -Gρ(r)M(r)/r²

Question 30

Evolution of stars according to mass

Answer 30

0.8 M☉ ≤ M ≤ 8M☉ progresses to white dwarf
8 M☉ ≤ M ≤ 30-40M☉ progresses to neutron star
M > 30-40M☉ progresses to black hole

Question 31

Cooling of white dwarf

Answer 31

t_cool = (GM²)/RL,

mass of WD ~ 0.6 M☉

Question 32

Age of universe

Answer 32

1/H₀*Mpc/km

Question 33

Luminosity in terms of radius of object and temperature

Answer 33

L = 4πR²σT⁴

Question 34

Diffraction proportionality

Answer 34

Δα ∝ λ/D

Question 35

Hubble’s law

Answer 35

v(km/s) = H₀*d(MPc)

Question 36

Temperature of earth

Answer 36

~290K

Question 37

Radiation pressure due to sun at distance d

Answer 37

P_rad = L☉/4πcd²

Question 38

3 zones in solar system

Answer 38

Inner zone: gases escape by radiation pressure, compact terrestrial planets
Middle zone: lots of ice, gas giants and icy giants
Outer zone: methane ice, no collisions bc low density, so Kuiper belt with small objects

Question 39

Core temp, mass and radius relation

Answer 39

T_c ∝ M/R

Question 40

Lifetime of a star

Answer 40

t = E/L, E energy

Question 41

H-R diagram

Answer 41

X axis temperature (decreasing)

Y axis luminosity (increasing)