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astro1 Flashcards

1
Q

How was time estimated at night for ancient egyptians

A

At night, time was estimated from the

position & phase of the Moon

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2
Q

How does Newton’s law of gravity extend Kepler’s laws?

A

1 Objects orbit their common center of mass (the point at
which 2 objects would balance if they were connected)

2 Allows the mass of a distant (massive) object to be
calculated IF you can observe another object orbiting it

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3
Q

What is the speed needed to orbit the earth in freefall

A

28000KMH

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4
Q

who saw sunspots on Sun (imperfections), mountains & valleys on the Moon (not
a perfect sphere)

A

Galileo

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5
Q

what is Stefan-Boltzmann Law

A

Stefan-Boltzmann Law explains the growth in height of

Planck’s radiation curve asT↑.

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6
Q

The Doppler effect refers to the

A

change in frequency of a
wave for an observer moving relative to the source of the wave.
 The amount of shift is proportional to the relative velocit

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7
Q

 Due to the Doppler effect:

A

The light (spectrum) of an object moving towards us is blueshifted  The light (spectrum) of an object moving away from us is redshifted

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8
Q

Doppler’s shift does NOT tell us

A

the tangential component of the object’s movement = how fast the object is moving across our line of sight

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9
Q

Long wavelength radio wave telescopes have to be

A

e very large to achieve reasonable angular resolution.  Angular resolution is proportional to wavelength λ

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10
Q

why are Ground-based telescopes at wavelengths outside

the transmissionwindows are completely useless!

A

Only certain wavelengths can be transmitted thru Earth’s

atmosphere:

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11
Q

Adaptive optics are used to

A

cancel out turbulences: the shape(s) of
the mirror(s) are computer-controlled to rapidly change so as to
compensate in real-time for the atmospheric distortions.
 For this purpose the image of a bright star (near the object of study) is
observed, OR an artificial one can be created by shining a powerful
laser beam into the sky

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12
Q

A basic lunar calendar has

A

r = 12 months, with some of 29 days and others
of 30 days
→ the final average has to agree with the approx. 29.5 day
lunar cycle
 A 12-month lunar calendar has only 354 or 355 days!

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13
Q

To avoid having their months cycle thru the seasons, some cultures used what

A

the fact that lunar phases repeat on the same
solar dates about every 19 years (because 19 solar years = 235 lunar
months) = Metonic cycle

1st recorded by Greek astronomer Meton in 432 B.C., though
Babilonians almost certainly knew about it)
 Lunar calendars that follow the Metonic cycle add a 13th month to 7
of every 19 years

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14
Q

 Early Greek philosophers, like Plato & Aristotle, adopted what model of the universe

A

geocentric model of the Universe:Earth at center of a celestial sphere with stars & planets orbiting
around it
 Heavens must be “perfect”: objects moving on perfect spheres or in
perfect circles

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15
Q

what are the limitations of the geocentric model

A

Hard for the geocentric model to explain the

apparent retrograde motion of planets.

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16
Q

Why did the greeks reject the idea of a sun centered model by aristarchus

A

KEY REASON: their
inability to detect the stellar parallax
 they believed all stars lie
on the same spher

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17
Q

what was the copernican revolution

A 
 His Heliocentric Model:
 Sun is at the center of the universe.
 Earth orbits like any other planets.
 Inferior planets have smaller orbits.
 Retrograde motion occurs when Earth “laps” Mars & the other
superior planets.
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18
Q

why was the copernican model incomplete

A

The model had the right general ideas but its predictions were not
much better than those of Ptolemy’s Earth-centered model
because:
 Copernicus held fast to the belief that heavenly motion must occur in perfect
circles
 Still needed to use epicycles to make decent predictions
 As complex as Ptolemaic model but still not more accurate!

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19
Q

what did tycho brahe do

A

: performed many accurate & comprehensive astronomical & planetary observations

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20
Q

what did johannes kepler do

A

used Tycho’s observations to discover the truth about planetary motion and eventually deduced what now are known as Kepler’s Laws of Planetary Motion which finally revealed the underlying truth of planetary motion & became accepted as a general model of Natural laws.

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21
Q

Kepler’s First Law

A

The orbit of each planet around the Sun is an ellipse with the Sun at one focus.  Nothing at the other focus

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22
Q

Kepler’s Second Law

A

As a planet moves around its orbit, it sweeps out equal areas in equal times.  A planet travels faster when it is nearer to the Sun & slower when it is farther from the Sun  It is actually an embodiment of the law of conservation of angular momentum L for the orbiting object of mass m

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23
Q

Kepler’s Third Law

A

More distant planets
orbit the Sun at slower
average speeds, obeying
the relationship:
p2 =a3 p = Orbital period, in[years]
a= Average distance from Sun, in [AU] …

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24
Q

Oort Cloud

A

Even more comets orbit the Sun in a distant, spherical region about a light-year away.

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25
Q

Kuiper Belt

A

Comets are ice-rich, & many are found in the region beyond Neptune.

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26
Q

Asteroid Belt

A

Region between Mars & Jupiter where asteroids, made of metal & rock, orbit.

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27
Q

what is mercury mostly made of

A

 Made of metal (mostly Fe) & rock: most metal-rich of all planets!

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28
Q

describe the atmosphere of mercury

A

No atmosphere:
 No wind, no rain
 stars can be seen even in daytime!
 Very hot (during the day) & very cold (at night)

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29
Q

what is the rotation of mercury

A

it

rotates exactly 3 times for every 2 of its orbits of the Sun

30
Q

what is the length of a day in mercy

A

176 earth days

31
Q

what is the volcanic and tectonic activity in mercury

A

No current volcanic or tectonic activity. However, there is evidence
of past geological activity:

32
Q

are there lava plains in mercury

A

lains created by ancient lava flows

33
Q

what planet has the most massive atmosphere of the terrestrial planets

A

vennus

34
Q

describe the atmosphere of venus

A 
Atmosphere has no O
2 or liquid H2O, 96% CO
2 & pressure =
92pEarth
 intense greenhouse effect
 temperature of 470°C
day & night
 Hellish conditions!
35
Q

what hides the surface of venus from view

A

by dense clouds of H

2SO

36
Q

what are the winds like in venus, if I wanted to go kite surfing

A

High speed winds keep the thick clouds in constant motion: they zip around
the top of the planet’s atmosphere every 4 days! However, close to the
surface wind speeds drop to only a few km/h.

37
Q

what is the length of a day on venus

A

A long solar

day of 117 days!

38
Q

where does the sun rise on venus

A

west

39
Q

name a planet that doesn’t have a magnetic field

A

venus

40
Q

what is a sidereal year

A

Time for Earth to complete one orbit around

the Sun

41
Q

what is a tropical year

A

Time for Earth to complete one full cycle of

seasons = the time from one spring equinox to the next one.

42
Q

what is a sidereal period

A

Time for a planet to complete one orbit around the

Sun.

43
Q

what is a synodic period

A

Time between the moments when a planet is lined
up with the Sun in our sky at one time and the next similar
alignment.

44
Q

what is a planet’s line up with the sun called

A

called a conjunction;

45
Q

what do we call an “opposition”

A

When the planet appears in a position exactly opposite to that of
the Sun (i.e., if you were on that planet you would see Earth
‘eclipsing’ the Sun)

46
Q

Which planets can never have an opposition

A

inner planets (closer from the Sun than Earth: Mercury, Venus):

47
Q

Which planets will have two conjunctions

A

inner planets (closer from the Sun than Earth: Mercury, Venus):

48
Q

what is a superior conjunction

A 
when the planet appears behind
the Sun (i.e. is eclipsed by the Sun)
49
Q

what is the diameter of an eclipse

A

within
umbra (an area ~270 km in
diameter on Earth’s surface)

50
Q

what is a partial solar eclipse

A

within
penumbra (an area ~7,000 km
in diameter on Earth’s surface)

51
Q

what is an annular solar eclipse

A

Moon
is relatively further away & its
umbral shadow does not reach
Earth

52
Q

what are the two types of eclipses

A

Lunar Eclipse = Earth is between Sun & Moon.

 Solar Eclipse = Moon is between Sun & Eart

53
Q

what are the conditions for an eclipse to occur

A

The phase of the Moon must be full (for lunar eclipse) or new (for solar
eclipse)
 The new or full moon must occur during one of the periods hen the nodes
of the Moon’s orbit are aligned with the Sun and Earth

54
Q

what is the saros cycle

A

18 years 11

⅓ days

55
Q

what makes eclipses recur in a cycle of 18 years 11

⅓ days

A

The combination of changing dates of eclipse seasons and

the 29.5 days cycle of lunar phases

56
Q

What causes the phases of the moon

A 
The amount of the
illuminated half visible
from Earth depends on
the Moon’s position on
its orbit
57
Q

what is the precession of earth

A

The direction of Earth’s rotation axis is not
fixed in space but executes a slow
precession (like a top) with a period of
26,000 years

→ Precession = a gradual
wobble that alters the orientation of
Earth’s axis, which thus sweeps a circle
at a slow rate

58
Q

what is the north star

A

polaris

59
Q

where is earth’s axis pointed at

A

polaris

60
Q

where will earth’s axis be pointing in 13000 years

A

axis will point to Vega (within

a few degrees).

61
Q

does earth’s precession change due to precession

A

It does NOT change the axis tilt which

stays close to 23.5

62
Q

Do the Positions of solstices & equinoxes in Earth’s

orbit gradually shift with cycle of precession.

A

yes

63
Q

where does earth get most of it’s direct sunlight

A

on the equinoxes, & its

least direct sunlight on the solstices.

64
Q

where are the seasonal variations around the time of solstices more extreme

A

high latitudes

65
Q

when do equinoxes occur

A

2 days of year on which the Sun rises precisely due E and sets precisely due W

66
Q

Why doesn’t the orbital distance affect our seasons

A

Earth is only 3% farther from the Sun at aphelion than at
perihelion.
Small variation overwhelmed by effects of axis tilt

67
Q

what are the four special moments in the year

A

 Summer Solstice (21 June)
 The Nern hemisphere receives its most direct sunlight
 Winter Solstice (21 December)
 The Nern hemisphere receives its least direct sunlight
 Spring Equinox (21 March)
 The Nern hemisphere just starts to tip towards the Sun
 Fall Equinox (22 September)
 The Nern hemisphere just starts to tip away from the Sun

68
Q

how many months does the sun spend north & south of the celestial equator in a year

A

6 months

69
Q

What constellations can one see?

A

It depends on your latitude & time of the year The altitude of the celestial pole in your sky is equal to your latitude The constellations you see depend on your latitude but not longitude.
 Because latitude affects the locations of the horizon & zenith relative to
the celestial sphere

70
Q

What are circumpolar stars

A

Circumpolar stars always reside above the horizon, and for that reason, never rise or set. All the stars at the Earth’s North and South Poles are circumpolar. Meanwhile, no star is circumpolar at the equator.

71
Q

how long was the entire process of accretion when the planets were forming

A

The entire process took less than ~50
m years
 Known from age of the oldest rocks in the solar system

72
Q

what is the most reliable method to measure a rock’s age

A

radiometric dating

astro (14 decks)

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