unit 2 | tides & distances 🌊

apogee

point of an orbit that is further away from focal point

perigee

point of an orbit that is closer to focal point

spring tide

• occurs during the full & new moon

  • the combined gravity of the sun & moon produces a stronger tide

    • higher high tide & lower low tides

  • has nothing to do with the season

  • occurs twice each lunar month

  • moon is aligned with sun

neap tide

• occurs during the waxing & waning half-moons

• the detracting gravity of the sun and moon produces a weaker tide

  • lower high tides & higher low tides

diurnal tide

• 1 episode of high water and 1 episode of low water each day

• occur in locations when the moon is farthest from the equator

semi-diurnal tide

• 2 episodes of equal high water and 2 episodes of low water each day

• the second high tide rises to the same level it did in the 1st high tide

• the second low tide also matches with the 1st low tide

• occurs when the moon is directly over the equator

• most common type of tidal pattern

mixed tide

• can have two episodes of high or low water per day

  • two high or low tides are unequal

• can either include both sets of unequal high or low waters or only one set of unequal high or low water

• occurs when the moon is extremely far north or extremely far south of the equator

meteorological tides

• tides affected by wind, barometric pressures, rainfall, ice melting, & land drying

• example:

  • storm surges: the wind & inverted barometric pressure combine to cause a dramatic increase in sea levels

doppler effect

• the apparent change in the frequency of a wave

• with light it’s also called “red shift, blue shift”

• when a star or other luminescent object is moving away from our position then it appears to give off more red light

• when a star or other luminescent object moves closer it appears to give off more blue light

cosmological red shifts

• the wavelength at which the radiation is originally emitted is lengthened as it travels through (expanded) space

• cosmological red shift results from the expansion of space itself and not from the motion of an individual body

astronomical units

• major unit used to measure space (AU)

• made from measuring the mean distance from the center of the Earth to the center of the Sun

  • 93,000,000 mi

light years

• how long is a light-year in Earth years?

  • 5,878,625,370,000 mi (9.5 trillion km)

parallax

• the apparent displacement or the difference in apparent direction of an object as seen from two different points not on a straight line with the object especially

OR

• the angular difference in direction of a celestial body as measured from two points on Earth’s orbit

parsecs

• a unit of distance used in astronomy, equal to about 3.26 light years (3.086 x 10^13 km)

• one parsec corresponds to the distance at which the mean radius of the Earth’s orbit subtends an angle of one second of arc