Understanding the night sky

Cards (48)

    • We measure the sky using angles.
    Pinky= 1 degree
    3 finger (index, middle and ring finger)= 5 degree
    closed fist= 10 degree
    Index and pinky= 15 degree
    thumb and pinky= 25 degree
  • Full circle = 360 degree = 2 pi radians

  • Angles in degrees= 360 degrees
    Angles in Arcminutes= 21600' minutes
    Angles in Arcseconds= 1296000" seconds
  • Whose Idea was angular measurement = 360 degrees?
    The ancient Sumerians around 3000BC.
  • An objects's angular size appears smaller if it is farther away.
  • A proper motion is how much an object moves (in angle on the sky compared to the stars) per unit time
  • Angular speed is an object moving with a velocity will have a proper motion because its physical position changes with time.
  • Angular resolution is the angle at which 2 points of light can be distinguished
  • Anatomy of the milky way
    A) Globular clusters
    B) Disc
    C) Stellar halo
    D) sun
    E) bulge
  • Stars at different distances all appear to lie on the celestial sphere
    • North celestial pole is directly above the Earth's North pole.
    • South celestial pole is directly above the Earth's South pole.
    • Celestial equator is a projection of Earth's equator onto sky.
  • Ecliptic is the sun's apparent path through the celestial sphere.
  • Zenith: the point directly overhead.
    Horizon: all points 90 degrees away from zenith.
    Meridian: line passing through the zenith and connecting N and S points on the horizon.
    A) Zenith
    B) Horizon
  • Latitude : position north and south of the equator.
    Longitude : position east and west of prime meridian.
  • The sky varies with latitude but not longitude.
    • Stars near the north celestial pole are circumpolar and never set.
    • We cannot see stars near the south celestial pole.
    • All other stars (sun, moon, planets) rise in east and set in west.
  • As the Earth orbits the sun, the sun appears to move eastward along the ecliptic.
  • At midnight, the stars on our meridian are opposite the sun in the sky.
  • Why do the constellations we see depend on latitude and time of year?
    • Depends on latitude because your position on earth determines which constellations remain below the horizon.
    • Depends on time because Earth's orbit changes the apparent location of the sun among the stars.
  • Seasons depend on how Earth’s axis affects the directness of sunlight.
    1. Summer solstice - June
    2. Winter solstice - December
    3. Spring equinox - March
    4. fall equinox - September
  • Sun's path across the sky:
    • Summer Solstice: highest path; rise and set at most extreme north of due east.
    • Equinoxes: sun rises due east and sets due west.
    • Winter solstice: lowest path; rise and set at most extreme south of due east.
  • Seasonal changes are more extreme at high latitudes
  • Earth's axis points in the same direction (to Polaris) all year round, so its orientation relative to the sun changes as Earth orbits the Sun.
  • Summer occurs in your hemisphere when sunlight hits it more directly; winter occurs when sunlight is less direct.
  • Axis tilt is the key to the seasons.
  • How does the orientation of Earth's axis change with time?
    Earth has a 26000 year precession cycle that slowly and subtly changes the orientation of Earth's axis.
  • Sidereal day: Earth rotates once on its axis in 23 hours, 56 minutes, 4.07 seconds.
  • Solar day: the sun makes one circuit around the sky in 24 hours.
  • A solar day is longer than a sidereal day by about 1/360 because Earth moves about 1 degree in orbit each day.
  • The phases of the moon are a 29.5 -day cycle.
  • Phases of the moon:
    A) first quarter
    B) gibbous
    C) full
    D) gibbous
    E) last quarter
    F) crescent
    G) crescent
    H) Waxing
    I) waning
  • Waxing: Moon visible in afternoon/evening; gets fuller and rises later each day
  • Waning: moon visible in late night/ morning; gets less full and sets later each day.
  • Sidereal month: moon orbits Earth in 27.3 days. Earth and Moon travel 30 degrees around the sun during that time.
  • Synodic month: a cycle of lunar phases; takes 29.5 days ( which is 1/12 longer than a sidereal)
  • We only see one side of the moon because of synchronous rotation- the moon rotates exactly once with each orbit.
  • Eclipse: earth and moon cast shadows. The moon is in front of the sun.
  • Solar eclipses can occur only at new moon; Moon's shadow on Earth
  • solar eclipse can be partial, total, or annular
  • Partial solar eclipse: The Moon partially obscures the Sun.