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Mastering Astronomy notes 4-8


Department
Astronomy & Astrophysics
Course Code
AST101H1
Professor
Stefan Mochnacki

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Plate tectonics helps keep carbon out of atmosphere, keeping it cool (unlike venus
which has no plate tectonics and is very hot)
1) volcanoes release carbon dioxide into the atmosphere
2) the carbon dioxide dissolves in the rain
3) minerals and carbon dioxide is washed by the rain into oceans of the earth
4) they react together to form rock
5) plate tectonics drags the rock into the mantle where it is again released by out
gassing of volcanoes
Carbon cycle keeps the temperature of the earth not too cold or too hot
Small icy moons are more active than small rocky planets because a) icy
compositions b) heating source tidal heating
the ice on these moons requires a lower temperate to melt than the rocks on the rocky
planets. Rock melts at higher temperate. This is why tidal heating occurs easily on
icy moons. The ice melts enabling tidal heating to drive geological activity, more
likely to have geological activity than terrestrial planets (example: mercury and
Ganymede similar in size, Ganymede ongoing geological activity, mercury
geologically dead)
The small moons have irregular shapes, their gravities are too weak to force them
into spheres
Only large planets can retain enough heat to stay geologically active
blackbody—HOTTER, PRODUCES MORE LIGHT = SHORTER WAVELENGTH (blue side)
Asteroid Belt
In between orbits of Mars and Jupiter
Material left over from the formation of the solar system, prevented from turning into a
planet by tides from Jupiter
Jupiter thick atmosphere surrounding giant ball of liquid hydrogen
Io most volcanically active because of jupiters tides
Uranus Neptune mostly icy mixture
Uranus tipped on its side
Kuiper belt is ring of comets orbiting beyond Neptune
Leftover debris from formation of solar system
Asteroids: metal, rock asteroid belt
Comets: icy kuiper belt
Oort cloud: cloud of comets surrounding entire solar system
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Impactors hit surface faster than the speed of sound in rock, so they explode
Craters are always circular because they are caused by explosions
Larger impacts may produce shock waves which rebound off the planets’ interior
layers and thrust the center of the crater up, producing a central peak or terraces.
Over time erosion, tectonics and volcanism erase craters
More craters = older
The more cratered, the older the surface
Atmospheric pressure on mars too low to allow liquid water to exist
Jovian planets made mostly of ice which holds lots of gas
All 4 gas giants have rock, metal cores
Jupiter: more metallic H
Saturn has more liquid hydrogen, more gaseous
Uranus, nepture less gaseous, more ammonia, methane, water
Aurorae caused by charged particles streaming along planets magnetic field lines
into its atmosphere
Tidal heating responsible for internal heat in Io that generates volcanic actvitiy
Ios orbit elliptical because of orbital resonances where the 3 moons of Jupiter line
up, their tugs on each other make their orbits elliptical
Europa surface ice, TIDAL Heating, possible water under surface: ocean
ganymede geological activity, tidal heating
callisto: ice ball, no tidal heating, not part of orbital resonances
titan: liquid methane, rocks made of ice, only moon with thick atmosphere
level of geological activity on the jovian moons depend on their size
Galilean moons so active because of the tidal heating that goes on which drives
activity LIKE Ios volcanoes and ice geology on the others
Jupiters tidal force on Io leads to tidal heating since its elliptical orbit causes
different tides
jupiters tidal forces = tidal heating = elliptical orbits = different tides = orbital
resonances
Many other moons show signs of past or ongoing geological activity
Jovian planets have rings because they formed from the dust created in impacts on
moons that orbit the planets
Source: impacts on the moons, they are not NOT leftover from planet formation, too
small to have survived
Always being replaced
Jovian planets have many small moons that were captured, the outgoing small
impacts on moons blast off dust to form particles making rings
Other jovian planets ring are smaller, darker, less particles
Assignment 4
The tidal bulges face toward and away from the Moon, because they are caused primarily by the
gravitational attraction between Earth and the Moon. (Friction explains why the bulges are
slightly ahead of the Earth-Moon line, rather than directly on the Earth-Moon line;
Tides affect the entire Earth, but they are much more noticeable for the oceans because water flows so much more easily than
land. Still, the land rises and falls measurably (by about 1 ) with the tides.
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the animation shows that any location on Earth passes through both tidal bulges and both tidal minima (the places where the tides
are smallest) each day, which means two high tides and two low tides. Again, recall that this is true both of land and oceans,
though tides are more noticeable in the oceans because water flows so much more readily than land.
Tides are created by gravity, and the tidal force is caused by the fact that gravity weakens with distance. Therefore, the parts of
Earth that are closer to the Moon feel a stronger gravitational attraction to the Moon, and the parts of Earth that are farther away
feel a weaker gravitational attraction to the Moon. This varying gravitational attraction essentially stretches Earth along the Earth-
Moon line, creating tidal bulges on both sides.
the tidal bulges are largest and the tidal minima are smallest at full moon and new moon, because those are the times when the
tidal forces due to the Sun and Moon are aligned (and therefore add to one another). Therefore, high tides are higher and low tides
are lower at these times, which are called spring tides. (In contrast, we have neap tides at first- and third-quarter moons, when
high tides are not as high and low tides are not as low.)
The Sun exerts a stronger gravitational force on Earth, which is why Earth orbits the Sun. However, tides are caused by
the variation in the gravitational attraction across Earth. Even though the gravitational attraction between Earth and the Moon is
smaller than the attraction between Earth and the Sun, the Moon's much closer distance makes this attraction vary more across
Earth. That is why tides are due primarily to the Moon, with only a secondary effect from the Sun.
The farther away an object, the smaller its parallax. In the animation, the mountains are so far
away that they do not have a noticeable parallax shift at all. The trees are farther away than the person,
so they have a smaller parallax shift.
Stellar parallax works just like the parallax of the person and trees in the Intro 1 animation. Just as the person and trees only
appeared to move because the photographer moved, we see stellar parallax only because we view stars from different positions in
our orbit at different times of year. And just as the person in Intro 1 has a greater parallax shift than the more distant trees and
mountains, stars nearby have a greater parallax shift than more distant stars. Therefore, stellar parallax provides direct proof
that Earth is not stationary at the center of the universe, but rather is a planet orbiting the Sun; if Earth did not move
around the Sun, there would be no apparent shift in stellar positions.
new and full Moons tides are most pronounced (highest high tides)
Suppose a lone asteroid happens to be passing relatively near Jupiter (but not near any of its
moons), following a hyperbolic orbit as it approaches Jupiter. Which of the following
statements would be true?
The asteroid's orbit around Jupiter would not change, and it would go out on the same
hyperbolic orbit that it came in on.
Assignment 5
-Notice that these wavelengths span an enormous range. The wavelengths of gamma rays can be
smaller than the size of an atomic nucleus, while the wavelengths of radio waves can be many
meters (or even kilometers) long. Visible light spans only a very narrow range of wavelengths,
from about 400 at the blue (violet) end to about 700 at the red end.
-The speed of light is a constant (in empty space) for all forms of light, meaning that all forms of
light travel at the same speed, regardless of wavelength, frequency, or energy.
-The prism bends different wavelengths of light by different amounts, causing the white light from the Sun to spread out into a
rainbow of colors. Absorption features appear as dark lines against the brighter background of the spectrum.
-The Suns hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular
wavelengths: why suns spectrum has black lines
-The Suns spectrum is an absorption line spectrum, which is produced when continuous light from a hot source (the Suns interior)
passes through a cooler cloud of gas (the gas that makes up the Sun’s visible surface).
-One of the two laws of thermal radiation (Wien’s law) states that the peak wavelength of a spectrum is directly related to an
objects temperature. A peak at yellow-green wavelengths corresponds to a temperature of about 5800 K.
-Each chemical element (or ion or molecule) produces a unique set of spectral lines; the wavelengths of these lines can be
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