astrophysics

• orbits of planets are ellipses
• planets in order from the Sun :

  1. mercury
  2. venus
  3. earth
  4. mars
  5. jupiter
  6. saturn
  7. uranus
  8. neptune
• star = luminous object at the centre of each star system. Our star : Sun
• comets = generally lumps of ice and rock
• moons = non luminous object that orbits planets
• planet = non luminous object that orbits a star. roughly spherical and dominate an orbit
• natural satellite = naturally placed without human intervention
• artificial satellites = 'man made', launched into space to orbit earth or another body in space by humans
• how do we distinguish between inner(terrestrial + outer planets (gas giants)?


  INNER

  • shorter orbits
  • solid surface
  • slower spin
  • rock and metal

  OUTER

  • larger orbits
  • faster spin
  • gas + liquid
  • made from hydrogen and helium
• what is the location of asteroid belt?

  between mars and jupiter
• what is the composition of the asteroid belt?


  contains lots of solid irregularly shaped asteroids or minor planets.
• almost all the stars we see in the sky are part of the Milky Way galaxy
• a galaxy is a gravitationally-bound group of billions of stars
• the nearest large galaxy to the Milky Way is the Andromeda Galaxy
• mass is constant and is the measure of type + number of atoms or molecules
• weight is the pull of gravity on an object and depends on strength of gravitational field strength
• weight = mass x gravitational field strength
• orbital speed= (2 x π x orbital radius) / orbital time period
• the Moon's spin period is equal to its orbital period about the Earth
• what are the Kuiper Belt and the Oort Cloud?

  The Kuiper Belt is outside of Neptune and contains small icy bodies that are considered the source of comets. The Oort cloud is outside of pluto and also has icy and rocky bodies
• seasons :

  • the earth orbits the sun with a slight tilt of 23.5 degrees
  • throughout the year, different parts of the earth receive the Sun's most direct rays more than others.
  • during winter in the northern hemisphere, the north pole is pointing away from the Sun & so the northern hemisphere doesn't receive as much light from the Sun, so the Sun won't heat the Earth up as much
  • the southern hemisphere and the south pole point towards the Sun so they get more hours of sunlight during the day causing a greater heating effect
• solar eclipse happens when the moon passes between the sun and the earth
• lunar eclipses happen when the earth passes between the moon and sun and blocks the sun's light on the moon
• moon phases :

  as the moon orbits around the Earth, sunlight reflects off the moon surface, light reaches the surface. Moon takes 30 days to orbit earth and the moon phase depends on where the moon is in the orbit.
• the moon and Sun appear the same size in our sky because the Sun is 400 times larger than the moon but 400 times further away from the Earth
• to find out how fast a planet is moving around the sun:

  • speed = distance/time
  • Speed = 2pir/time taken for one orbit
• Newton's Cannon:

  • Newton asked 'what if we kept firing a cannonball further and further'
  • conclusion = if we fire the cannon with enough velocity it would dip over the edge of the horizon and keep falling and never crash back to Earth
  • these are the exact conditions needed for an orbit: the object has so much horizontal velocity that the gravitational force from the Earth is not able to pull the object back to earth - the object is constantly falling
• during the crescent phases the moon is visible during daytime
• waning crescent moon: moon is waning, moon is not full, moon is not round
• waxing crescent moon: moon is waxing, the light is getting stronger and the moon is getting bigger than new moon
• waning gibbous moon = before full moon shaded on the right
• waxing gibbous moon = before full moon shaded on the left