Earth Science Movements: Rotation & Culmination Height

• Study notes on earth science movements by Ada Van Moer

Earth Rotation

• The day arc of the sun refers to the apparent movement of the sun on the celestial dome.
• 0 = West
• Culmination height signifies the highest point the sun reaches.
  • This height varies in size due to earth's revolution and axis.
• Zenith is the point directly above the observer on the celestial dome.
• During the day, the sun illuminates half of the Earth.
• Culmination height differences determine the day-night ratio.

Culmination Height Differences (March 20 / September 23)

• Occurs during spring and autumn.
• 0 = West
• Day and night are of equal length.
• CH = 40°
• 90° - GB (50°)

Culmination Height Differences (June 21)

• Occurs during summer.
• NO = NW
• Day is longer than night.
• CH = 63°26'
• 90° - GB (50°) + 23°26'

Culmination Height Differences (December 22)

• Occurs in winter.
• ZO- ZW
• Day is shorter than night.
• CH = 16°34'
• 90°- GB - 23°26'

Stars

• Stars appear to revolve around a single point, the North Star.
  • It lies in line with the Earth's axis.

Apparent Movement Explained by Actual Movement

• People move, but the sun would need to move faster for this to be observed.
• The apparent movement of the sun is from East to West.
  • The Earth's actual movement is from West to East, counterclockwise.
    • This is earth's rotation.
    • 1 rotation takes 24 hours.

Determining Location on Earth

• Worldwide grid exists for this purpose
  • The world coordinate system
    • Each location on Earth describes a circle known as latitude circles or parallels.
      • Giving West and East directions.
    • All locations where the sun culminates at the same moment lie on the same meridian.
      • Giving North and South directions.
    • 2 null lines:
      • Equator
        • longest latitude circle.
        • The dividing line between the Northern Hemisphere (equator - 90°N) and the Southern Hemisphere (equator - 90°S)
      • Prime Meridian
        • Passes through Greenwich.
        • Divides the Eastern Hemisphere (meridian - 180°O) and the Western Hemisphere (meridian - 180°W).
        • 180°W = 180°O.

Coordinates in the World Grid System

• Coordinates refer to a point relative to the null lines.
  • Expressed in degrees.

Latitude/Geographic Latitude/Altitude of the Pole

• Distance from point to equator.
  • Measured along local meridian.
    • Northern latitude/southern latitude.

Longitude/Geographic Length

• Distance from point to the prime meridian.
  • Measured along the local latitude line.
    • Eastern longitude/western longitude.

Time Zones on Earth

• Longitude determines when a part of the earth is lit, leading to time differences.
  • Solar time
    • Time based on the culmination height is used as true time, without it land can have a vast difference in time.
    • Oostende is 12 minutes later than Eupen

Time zone theory

• 360° = 24U = 1U = 15°.
• The prime meridian is central in the first time zone (UTC).
• 1° = 4 min

Conventional Time or Local Time

• Time zones are adapted to the country borders.
  • Winter time = UTC +1
    • Last Sunday of October.
  • Summer time = UTC +2
    • Last Sunday of March.

Time Zones in Belgium

• Not exactly UTC, but closer W0 will be UTC +1
  • Summer months: OET (+1)
  • Winter months: MET (+2)

Date Line

• Meridian located at 180°.
  • From NM to 180°O = 12 hours later.
  • From NM to 180°W = 12 hours earlier.
• Date changes when the date line is crossed.
  • East to West = previous day.
  • West to East = next day.
• Modified line: Kiribati.

Wind and Current Deflection

• Speed at which Earth rotates affects where an object lands
  • Equator: 1656 km/h.
  • In the region: 1044 km/h.
  • North Pole: 0 km/h.
• Different rotational speeds cause deflection.
  • Coriolis force/effect.
    • Acts on water and air currents.
    • Deflection in the Northern Hemisphere is to the right.
      • Deflection in the Southern Hemisphere is to the left.
    • From equator to North/South = faster → right.
    • From North/South towards equator = slower → left.

Earth Flattening

• Increase in centrifugal forces towards equator results in the expansion of the equator and flattening of the poles.

Earth Revolution

• Earth revolves around the sun in a counterclockwise motion.
• Apparent vs. Actual movement.
  • Earth's revolution and tilted axis cause variations in the sun's arc at different locations and times, affecting culmination height and sunrise location.

The Elliptical Orbit of the Earth Around the Sun

• Earth revolution = elliptical orbit.
  • Imaginary plane = ecliptic plane.
    • Distance between points not always regular.
  • Distance between A-Z doesn't affect temperature.
• Aphelion
  • Begins in July.
  • Refers to the greatest distance
• Perihelion
  • Begins in January.
  • Refers to the smallest distance.

Three Laws of Kepler

• Law of Orbits/Ellipses
  • Every planet moves around the sun in an elliptical orbit, not a perfect circle, with the sun acting as one of the focal points.
• Law of Areas
  • A line from the sun to a planet sweeps equal areas in equal time intervals.
  • A planet moves faster when closer to the sun and slower when farther.
• Law of Periods
  • The speed of planets depends on their distance to the sun.
    • orbital period2 = (half the long axis of the orbit)3

Earth Revolution Determines the Calendar Year

• Time between 2 astronomical springs
  • 365 days, 5 hours, 48 minutes, and 46 seconds is one year.
• Leap year every 4 years = Julian calendar.
  • Rounding not accurate so leap year if divisible by 4 unless century years, except multiples of 400 = Gregorian calendar.

Seasons

• Earth is angled at 23°26'.
  • → NP and ZP equal to half the day and half the night
    • seasons (sun arc and amount of sun and the energy will vary)

Spring and Autumn Equinox

• The sun's rays hit the equator at a perpendicular angle on March 20 and September 23.
  • Resulting in both hemispheres being equally lit.
    • Leads to equal day and night length = equinox
      • March 20 = spring equinox (NH) or autumn equinox (SH).
        • Begin of astronomical spring.
      • September 23 = autumn equinox (NH) or spring equinox (SH).
        • Begin of astronomical autumn.

Summer Solstice (NH)

• Sun's rays hit the Tropic of Cancer at a perpendicular angle on June 21.
  • Illuminating the Northern Hemisphere.
    • Leads to longer days (NH).
      • Sun rises North East and sets North West
        • Astronomical summer = summer solstice
        • North Pole: polar day, South Pole: polar night.

Winter Solstice (NH)

• Sun's rays hit the Tropic of Capricorn at a perpendicular angle on December 22.
  • Enhancing the sun light in the southern hemisphere
    • Day shorter than night (NH).
      • Sun rises south east and sets south west
        • Astronomical winter = winter solstice
        • North Pole: polar night, South Pole: polar day.

Culmination Altitude

• Summer: highest point of culmination in the North.
• Culmination differences determine the climate zones.
  • Cold/polar climates (2 seasons).
    • From the polar circles to the poles.
  • Moderate/intermediate climate (four seasons).
    • Pool circles to tropics
      • Day Length varies
    • Warm/tropical climates (high temperatures all year).