Astron MT 1
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School
University of California, Berkeley *
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Course
10
Subject
Astronomy
Date
Jan 9, 2024
Type
Pages
4
Uploaded by DukeTigerPerson976
Can we determine chemical composition of a star's outer layer of gas by it’s absorption lines?
YES
The time it takes to travel from the Earth to the Sun is (closest to)…
10 min because the distance is 1 AU which is equal to 8.3 light minutes
If we double the diameter of a telescope’s primary mirror or lens, the light-gathering power
increases by a factor of what?
EQUATION APPLICATION QUESTION
= ratio of light gathering power
(
𝐷2
𝐷1
)
2
Light gathering power is determined by area (and thereby diameter
squared)...distance/length of telescope is NOT a factor in light gathering power. The
bigger, the more it can collect.
D2 in this case doubled, so 2:1 squared means the light gathering power increases by a
factor of 4
Which of the following statements is true?
a.
If you see a star overhead at midnight on August 7th, you will see it overhead at 4am
October 7th.
i.
This is incorrect. Stars rise 4 minutes earlier per day, which is about 2 hours a
month. It will therefore rise 4 hours earlier in this two month period. Four hours
earlier
than midnight is 8pm.
b.
The stars within a given constellation are all approximately the same distance from
Earth.
i.
This is incorrect. Constellations are amalgamations of stars that, from our
perspective, form identifiable formations. However, one star's brightness may be
due to its surface area being big (but perhaps far), another to its physical
distance being close (but perhaps small). Either way, these stars happen to have
similar brightness irrespective of their distance from us.
c.
Over the course of a year, a person in Berkeley can see the entire sphere at night.
i.
Only at the equator can people see the entire sphere over the year. At the poles,
you virtually see the same stars the entire year. The below option is correct
because in Berkeley, you will see some of the celestial southern hemisphere, so
there will be overlap.
d.
Some parts of the celestial sphere visible in Berkeley in December are visible in the
South Pole in June.
Imagine we are viewing a hot star through a cold cloud of gas. Which of the following best
describes what we would see in its spectrum?
★
A spectral line caused solely by a drop to a lower energy level is an emission line. When
continuous radiation falls on cool gas, atoms can be raised to higher levels resulting in
absorption lines. If we look at a star under a cool cloud of gas in our line of sight, we will
see absorption. So the answer is
a.
a continuum, with absorption lines from the gas superimposed
True or False: Venus undergoes retrograde motion when it is on the same side of the Sun as
Earth.
Which of the following is
not
a consequence of Newton’s laws?
Newton’s laws of motion are
If no forces act on a body, its speed and direction of motion stay constant
Force = mass x acceleration
When two bodies interact, they exert equal and opposite forces on each other
D. If two satellites orbit Earth at the same distance, the satellite with the greater mass
will feel a greater acceleration than the one with less mass.
●
This question asks about acceleration. The acceleration of an orbiting
body is independent of its own mass. It depends on the mass of the
central object (multiplied by gravity) and (divided by) the distance
squared. Thus, acceleration differences would occur if the mass of the
central object or the distance between the central and orbiting objects
changed. Newton’s equation of force based on the central and orbiting
body is given on the cheat sheet, but important to note that the equation
is equal to the mass times acceleration of the orbiting object, and thus
you see how acceleration of the orbiting object is dependent on the
described info above. (see scratch for visual)
Imagine a star with a single exoplanet orbiting it. If the exoplanet’s mass were doubled, the
observed Doppler-shift variations of the star would be
? If the semimajor axis of the
exoplanet’s orbit were doubled, the observed Doppler-shift variations would have a
?
If a planet's mass is doubled, the gravitational force increases based on Newton’s orbital
laws of motion. Additionally, if the semimajor axis doubles, the period of the planet would
be longer and thus the Doppler observations would have longer periods.
a.
Larger; longer period
True or False: Water faucets and showers in bathrooms typically have blue indicating cold and
red hot because cold objects emit light of shorter wavelengths.
Which phase of the moon rises at approximately 9pm?
True or False: Rounding to the nearest 5%, the species Homo Sapiens (humans) first appeared
when the Earth was about 90% of its current age?
We are only about 300,000 years old and would have been here for 2 seconds on a 24
hour timescale. So, more like 100%!
If Star Ben is two times as hot than Star Geri, which is not necessarily true?
Stephan Boltzman law says energy emitted per second is based on temperature.
The product of surface temperature and wavelength peak is constant.
Luminosity depends on both radius (size) and temperature, so if a star is hotter but much
less smaller, it may be less luminous than a bigger, cooler star.
b.
Ben is more luminous than Geri
Correct ranking of gravitational force between Moon/Earth?
a.
Gravitational force exerted by Moon on Earth is lesser the further away
Which of the following statements about comets is true?
a.
The time interval where a comet’s tail is long is shorter than when it is shorter.
They spend very short amount of time by sun
They form in Kuiper or oort cloud
Their periods range from 200 yrs to millions
True or False: Chromatic aberration in our eyes causes stars to twinkle
Chromatic aberration is when white light is tinged with color and out of focus when light
passes through a simple lens because there is no single best focus.
The point-like image of stars seen through Earth’s turbulent atmosphere cause them to
twinkle in our line of sight (as opposed to the disk-like images of planets consisting of
many individual twinkling points that average out)
Terrestrial vs Jovian
Terrestrial planets are smaller and more dense. As far as day/night cycles, the Jovian
planets spin faster so their days are shorter, but orbital periods around the Sun are bigger
because they are much further.
More…
●
For energy and wavelength, remember MORE energy is SHORTER wavelength.
●
Being transparent to visible light means you can collect light, while being opaque to
infrared means you can absorb it/trap it. (why Venus is the hottest planet with this
extreme greenhouse affect)
●
Blue sunlight is preferentially scattered by air molecules while red/orange is transmitted.
●
The main reason Pluto is not a planet is because it has not cleared its surrounding
objects from its neighborhood, it is not a “bully”.
●
A given total lunar eclipse can be seen from more than half of Earth’s surface, but not a
total solar eclipse. Also, the moon must be in a new phase to see a total solar eclipse.
The two cannot happen within less than 2 weeks of each other.
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●
The Roche limit is the outside of a planet, where gasses are no longer held together by
their mutual gravity. Saturn’s rings are inside its Roche limit which is why they are spread
out rather than coalesced with the planet
●
Spherical lenses suffer from spherical aberration in which light cannot be perfectly
focused from very large distances because the rays are essentially parallel, while a
parabolic lens corrects this. (hubble suffered from the former)
●
Ptolemy’s geocentric model WORKED based on his theory of epicycles because you
can just keep adding more. Copernicus’s heliocentric model relied on perfect circles and
used epicycles too. The discoveries by Gaileo and Kepler substantiated his claim.
●
Electromagnetism is much stronger than gravity which is relatively weak… a moon
bound by only electromagnetic force wouldn't be destroyed in a roche limit of another
planet
●
Age of universe is 14 billion years old so we obviously aren’t seeing things older than
that
●
Low and high tides are most extreme when moon is new or full
●
There is a high tide on both ends of earth and low tides on top and bottom
●
Small moons can be found next to narrow rings and are why they stay stable
●
Crescent is before new and therefore before solar eclipse
○
Full, gib, quarter, crescent, new
●
We see craters on other planets more than earth because erosion on earth rids of
evidence relatively quickly