Astronomy Notes by ewghwehws

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									          Astronomy Notes
   The Lunar Orbiter 1 in 1966 disproved
  ancient travellers ideas of the shape of the
                      Earth.
Our current belief is based on the behaviour
  and evidence of moons, planets and stars.
As new evidence is discovered our belief may
             change in the future.
          Astronomy Notes
  Earth is one of 8 planets to orbit the sun
   Solar system or from the sun, mercury,
  Venus, earth, mars, asteroid belt, Jupiter,
          Saturn, Uranus, Neptune.
 The orbits are elliptical with the Sun at the
                     centre.
Gravitational field strength is the strength of
         gravity on a planet or moon
         Astronomy Notes
  Gravitational Field Strength on Earth is
                approx. 10N/kg
  Gravitational Field Strength on moon is
                    1.6N/kg
 Planets are non-luminous, do not give off
    light, they reflect light from the sun
Mercury, Venus, Mars, Jupiter and Saturn all
           visible by the naked eye.
           Astronomy Notes
Uranus and Neptune are so far away they were
    only discovered after the invention of the
                    telescope.
Planets held in orbit by gravitational pull of the
                        Sun.
Gravitational pull on Mercury is large compared
to that on Neptune, because Neptune is further
                       away.
  As a consequence Mercury follows a tighter
               orbit than Neptune.
           Astronomy Notes

 Moons are natural satellites that orbit a planet.
  Their motion depends on gravitation forces.
 Moons are also non-luminous, we see them as
          they reflect light from the Sun.
Earth’s moon is 400,000km away, has a mass and
            gravity 1/6th that of Earth.
  Moon has no atmosphere and has a surface
    covered with craters caused by impacts of
                    meteorites.
         Astronomy Notes
  Takes moon 29.5 days to orbit the Earth.
 Moon spins on its axis but more slowly than
                      Earth.
Completes one full rotation every 29.5 days.
      Moons rotation=Earth’s rotation
Therefore moon always keeps the same part
          of its surface facing Earth.
Some planets have many moons, Jupiter has
 over 60, some have a small number; mars 2.
         Astronomy Notes
                 Comets
          Comets orbit the Sun
       Approx 1-30km in diameter
          Made of ice and dust
          Orbits are elongated
  Sometimes they are quite close to the
 sun(strong gravitational pull=fast speed)
While other times they are far away (weak
      gravitational pull=slow speed)
          Astronomy Notes
  When it is close to sun the frozen gases
  evaporate, forming long tails that shine.
Most famous comet is Halley’s Comet, visible
          to earth ever 76 years.
          Astronomy Notes
Asteroids: minor planets or rocks, that orbit
                     the sun.
   Asteroid belt between Mars and Jupiter
    Can be few meters to several hundred
                   kilometers.
  First asteroid was Ceres, diameter 933km
 Believed that asteroids are broken parts of
                     planets.
          Astronomy Notes
                  Satellites
Satellites are held in orbit around a planet.
         Two types natural = moons
    Artificial = manufactured satellites
         Astronomy Notes
           Gravitational Forces
  1st thought of Universe in history was
Ptolemaic System where the Earth was the
      centre all planets orbited Earth
Later: Heliocentric where the Sun is at the
                   centre.
          Astronomy Notes
           Newton’s Law of Gravity
Gravitational force exists between two bodies
               They depend on:
       The masses of the two objects
     The distance between the masses
 Inverse Square law exists: see page 53 Fig
                      6.10
           Astronomy Notes
    Planets travel in orbits around the Sun
Sun contains 99% of the mass of Solar System,
 that's by sun holds the solar system together.
Speed of satellites depends on relationship of
circumference of the circular orbit and the time
                     it takes.
             Orbital speed = 2πr/T
R is the orbital radius and T is the time period
           Astronomy Notes
       See worked example on page 54
                   Milky way
  Sun is our nearest star approx 150 mill km
                      away.
        Surface temp= 15 mill degrees
Gravitational forces between stars cause them
                to form galaxies
      Galaxies consist of billions of stars
            Astronomy Notes
   Our galaxy is a spiral galaxy called Milky Way
 Universe is simply empty space within which are
        scattered large numbers of galaxies.
Astronomers believe there are billions of galaxies.
   Distance between galaxies are millions time
   greater than distances between stars within a
                        galaxy.
  The distances between the stars in a galaxy are
    millions of times greater than the distance
           between planets and the sun.

								
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