The Earth

  • An Oblate Spheroid
  • 12,724km Diameter (~13Km)
  • Equatorial diameter is 42km greater than the polar
  • Inclined 23.44° (~23.5)
    • Precession; wobble of the axial tilt; 25800 year cycle. Caused by the obliquitiy of the earth (equatorial bulge) in concert with the gravity of Sun & The Moon#
    • axial tilt or obliquity deviation from the parallel
    • In 12K years, the North Star will actually be Vega, not Polaris Precession from North

Celestial Sphere

  • Celestial equator - abstract projection of the terrestrial equator into space, and is the base of the equatorial coordinate system.
  • Ecliptic - the plane of earth’s orbit around the sun
  • South Celestial Pole - the point in the sky about which all the stars seen from the Southern Hemisphere rotate
  • North Celestial Pole - the point in the sky about which all the stars seen from the Northern Hemisphere rotate
  • Due to precession, celestial equator and equinoxes move and the year needs to be noted (the epoch)

Earth

  • Crust varies between 0-70km. Continental crust of low density rocks like granite. Thinner oceanic crust of denser rock like basalt

  • Tectonic platest floating on a silicate mantle

  • Mantle extends half way to the center, making up 80% of the volume. Lower mantle is solid, upper mantle convection currents which drive sideways movements of tectonic plates.

  • Outer Core 5000K, liquid Iron Fe, Some Nickel Ni

  • Inner Core 5500K, Same temp as sun’s photosphere, high pressure, solid. Ni, Fe

Core

Latitude and Longitude

Lat/Long are angles subtended (joined at point) at the center of the earth. Lat is E/W of Meridian, and N/S of equator

  • Prime Meridian passes through Greenwich, between N & S pole (agreed in 1884 in Washington DC)
  • Artic Circle 66°34’ N (66.5°N); at least one day with no sun during winter.
  • Tropic of Cancer 23°26’ N
  • Tropic of Capricorn 23°26’ S (between Cancer and Capricon, at least one day a year the sun is overhead)
  • Antarctic Circle 66°34’ S (66.5°S); at least one day with sun all day during winter.

Arctic and Antarctic circles are the furthest point where you can still see the sun set every day of the year.

Lat Long

  • Spring Equinox March 21st - Sun over the equator. Vernal Equinox - (Latin for spring)
  • Summer Solstice June 21st - Sun over Tropic of Cancer 23.5°N. Solstice - ‘Solar Standstill’ in Latin
  • Autumnal Equinox September 23rd - Sun over the equator
  • Winter Solstice December 21st - Sun over Tropic of Capricorn 23.5°S

In spring the sun rises exactly in the East, sets in the West. Also in Autumn. In winter, rises in the SouthEast, sets in the SouthWest, skims the horizon. Days are shorter. In Summer the sun rises in the NorthEast and sets in the NorthWest and days are longer.

Equinox Sun Orbit

Also see Sidereal Time

Atmosphere

Absorbs harmful radiation, UV and X-radiation, regulates temperature to mean 15° and protects from most meteoroid strikes

Blue sky because Nitrogen(N) and Oxygen(O2) scatter blue wavelengths of light, mostly. So the sky is predominantly blue. Air is always in turbulent motion, causing light to refract and change direction as it passes through the different layers. Causes stars to ‘twinkle’

Light pollution - Skyglow - a rusty orange haze by urban lighting. Glare from artificial lights such as streetlights, carparks, etc, making night vision harder dark adaption 200 stars in light polluted areas are visible, but 3000 where there is no light pollution Light pollution makes the sky brighter than the natural night sky, making it hard to observe faint objects such as galaxies or nebulas.

Seasons

  • The earth is nearer the sun in Winter. Angle of the earth/suns rays hitting it is what determines temperatures. Orbit Of Earth

From: Ecliptic

  • The distance of the Celestial Equator from the zenith is equal to your latitude. If the distance is south of the zenith, you are north of the equator, and vice versa.
  • The altitude (distance above the horizon) of the NCP is equal to your latitude north of the equator; ditto for the SCP in the Earth’s southern hemisphere.
  • The circumpolar stars are within (latitude) degrees of the celestial pole. They have declinations greater than +(90-latitude) degrees for the northern hemisphere.
  • The southernmost star visible from your location in the northern hemisphere is at declination -(90-latitude) degrees. The opposite situation applies in the southern hemisphere.
  • Those stars with declinations equal to your latitude pass directly overhead during the night. Logical sense, since stars are measured the same way declination is.

#TBD

  • Visit to Greenwich?
  • More info on Lat/Long
  • More on the earth’s crust/composition
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