Transcript Astrophysics

Astrophysics
History of Exploring the Universe
Done by
Zheng Han & Sun Bangjie
celestial sphere
Definition:
 In astronomy and navigation, the celestial
sphere is an imaginary sphere of arbitrarily
large radius, concentric with the Earth and
rotating upon the same axis.
 In the Aristotelic and Ptolemaic models,
the celestial sphere was imagined as a
physical reality rather than a geometrical
projection
system of coordinates
Definition:
 A coordinate (or co-ordinate) system is a
system for assigning an n-tuple
of numbers or scalars to each point in andimensional space
Constellations- in northern part
Newton's Law of Gravity
Each object in the universe attracts each other body.
If object A has mass Ma and object B
has mass Mb,
then the force F on object A is directed
toward object B and has magnitude
F = G Ma Mb / r2
So, considering the force between
an Sun and the Earth
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The force exerted on the Earth by the Sun is
equal and opposite to the force exerted on the
Sun by the Earth.
If the mass of the Earth were doubled, the force
on the Earth would double.
If the mass of the Sun were doubled, the force
on the Earth would double.
If the Earth were twice as far away from the Sun,
the force on the Earth would be a factor four
smaller.
Notes on the meaning of r:
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If the two objects are very small compared to the
distance between them, then the force is given by
Newton's formula with r being the distance between
the objects.
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If one of the objects is very small and the other is
spherically symmetric, then the same formula holds with
r being the distance from the small object to the center of
the big object.
Point two is a consequence of point one. Newton proved
it by adding up the forces.
Kepler's third law
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The average distance of a planet from the Sun
cubed is directly proportional to the orbital period
squared. Newton found that his gravity force law
could explain Kepler's laws. Since Newton's law
of gravity applies to any object with mass,
Kepler's laws can be used for any object orbiting
another object. Let's look at satellites orbiting a
planet.
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If you have two satellites (#1 and #2) orbiting a planet,
Kepler's third law says:
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(period #1/period #2)2 = (distance #1/distance #2)3,
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where the distance is the average distance of the
satellite from the planet---the orbit's semimajor axis. The
satellites must be orbiting the same planet in order to
use Kepler's third law! Kepler found this law worked for
the planets because they all orbit the same star (the
Sun).
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If you have measured the orbital period of one satellite
around a planet, you can then easily find how long it
would take any other satellite to orbit the planet in any
size oribt. Kepler's third law can be simplified down to
Structure and behavior of the solar
system
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The solar system is the star system we are now living in.
It consists of the sun, eight planets, sixty six satellites
and countless asteroids, comets and meteorites.
The order of the planets from the sun to the outside is
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus
and Neptune.
The planets that are near the sun like Mercury, Venus,
Earth, Mars are called terrestrial planets.
The same characteristics of them are of higher density,
with smaller volume, slower rotation, fewer satellites and
solid shell.
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The planets that are far away from the sun like Jupiter,
Saturn, Uranus and Neptune are called Jovian planets.
They all have thick atmosphere and the characteristics of
theirs surface are difficult to know.
Between Mars and Jupiter, there are more than 100000
asteroids.
Meteorites are between the planets.
These planets are moving around the sun on the
elliptical orbits.
Nature of Moon's motion and
eclipses
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The Moon orbits the Earth roughly once a month.
Looking down on the Earth and Moon from
above the Earth's north pole, we see that its
revolution is in the same direction as the Earth's
rotation (and also the Earth's revolution around
the Sun).
At new moon, we can't see any of the illuminated half of the Moon;
At full moon we can see all of it.
Halfway in between new and full moon, we see half of the illuminated half of
the Moon, or a quarter of the Moon.
First quarter occurs as
the Moon moves from
new to full; third or last
quarter occurs as the
Moon moves from full to
new.
Between the new and quarter moons, only a small fraction
of the Moon is illuminated; we call this a crescent moon.
Between the quarter and full moons a larger fraction of the
Moon is illuminated; we call this a gibbous moon.
When the Moon
moves from new to
full, it becomes more
illuminated, and we
say that it is waxing.
When it moves from
full to new, it
becomes less
illuminated, and we
say that it is waning.
Ecliptic
telescope
In fact, the telescope just makes the object become nearer
to our eyes. The image is lessened, inverted and virtual.
microscope
In fact, the microscope is used to twice magnify the
object in order to get a bigger image. The image is
magnified, upright and virtual.