Space Physics

• Orbital speed

  The speed at which a planet or moon orbits around another body
• Circular motion

  • In one orbit, a planet travels a distance equal to the circumference of a circle (the shape of the orbit)
  • This is equal to 2πr, where r is the radius of the orbit
• Earth

  A rocky planet that rotates in a near circular orbit around the Sun
• Orbital period (or time period)

  The time taken for an object to complete one orbit
• Orbital radius

  The distance from the centre of the object being orbited to the object orbiting
• Earth's axis

  • A line through the north and south poles
  • Tilted at an angle of approximately 23.5° from the vertical
• Earth's rotation

  • Completes one full revolution in approximately 24 hours (1 day)
  • Creates the apparent daily motion of the Sun rising and setting
  • Responsible for the periodic cycle of day and night
• Orbital radius should be measured from the centre of the body being orbited, not just the surface
• Day

  The half of the Earth's surface that is facing the Sun
• Units should be checked and converted if required when using the orbital speed equation
• Night

  The other half of the Earth's surface, facing away from the Sun
• Earth's rotation on its axis

  Makes the Sun look like it moves from east to west
• Equinox

  When day and night are approximately of equal length
• In the northern hemisphere

  • In summer, the sun rises north of east and sets north of west
  • In winter, the sun rises south of east and sets south of west
• Summer Solstice

  The day when the Sun is at its highest point in the sky all year
• Winter Solstice

  The day when the Sun is at its lowest point in the sky all year
• Earth's orbit

  Orbits the Sun once in approximately 365 days (1 year)
• Tilt of the Earth

  Combined with orbiting around the Sun, creates the seasons
• Over parts B, C and D of the orbit

  The northern hemisphere is tilted towards the Sun, meaning longer daylight hours than night (spring and summer)
• Over parts F, G and H of the orbit

  The northern hemisphere is tilted away from the Sun, meaning shorter days than night (autumn and winter)
• Moon

  A satellite around the Earth that travels around it in roughly a circular orbit once a month
• Moon's revolution

  Takes 27-28 days and it always has the same side facing the Earth
• Moon's light

  Shines with reflected light from the Sun, it does not produce its own light
• Phases of the Moon

  The way the Moon's appearance changes across a month, as seen from Earth
• New Moon

  The Moon is between the Earth and the Sun, so the sunlight is only on the opposite face of the Moon to the Earth, making it unlit and not visible
• Full Moon

  The Earth is between the Moon and the Sun, so the side of the Moon facing the Earth is completely lit by the sunlight
• In between new and full moon, a crescent can be seen where the Moon is partially illuminated from sunlight