Space Science Unit 4

earth facts: ellipticity

0.003353

earth facts: radius

6371 km (average)

earth facts: mass

5.97 × 10^24 kg

earth facts: circumference

24,901 km

earth's orbit: eccentricity

0.01671

earth average distance from the sun

152*10^6 km

axial tilt

the axis on which the earth spins is tilted with respect to its ecliptic, causes seasons. (23.5 degrees)

how does the earth's axial tilt cause the seasons?

during the year, different parts of Earth receive the Sun's most direct rays (distance to the sun do not affect seasons)

summer solstice

• earth's tilt towards the sun is the highest

• day with the most hours of sunlight and the fewest hours of darkness (June 21)

• angle of sun: 70.6 degrees

• daylight hours of the summer solstice:

  • north pole: 24 hours

  • Boston: 15.13 hours

  • Hawaii: 13 hours

winter solstice

• earth's tilt away from the sun is the highest

• day with the least hours of sunlight and the most hours of darkness (December 21)

• angle of sun: 24.6 degrees

spring/vernal and autumnal equinox

• earth's tilt is neither tilted towards or away from the sun

• daylight hours are exactly the same

• angle of sun: 47.6 degrees

• at the equator, the sun is directly overhead

• occurs twice per year (each occurring once)

• occur in March 21/September 21

• 12 hours 10 min of daylight in Boston

why is it hot at the equator but cold at the poles?

• equator receives the most amount of sunlight, therefore receives the most solar energy

• energy spreads out over large areas with increasing latitude

• the greater the land area the energy spreads across, the lower the energy per unit area.

moon facts: ellipticity

0.0012

moon facts: radius

polar: 1736 km

equatorial: 1738 km

average: 1737 km

moon facts: mass

0.07*10^24 (1.2% of Earth)

moon facts: distance from earth

384,399 km

moon facts: surface gravity

1.62 m/s² (17% of earth)

moon's orbital tilt

5 degrees (0.05)

synchronous rotation

• time it takes for the moon to spin once around on its own axis = time it takes for the moon to complete one orbit around the Earth, this is basically the definition of synchronous rotation (27.3 days)

• one one side of the moon is shown to us at all times

• since the moon's center of gravity is lower than its center of mass, it cannot rotate on its axis any faster because the same side is always being pulled towards the earth

moon phase

• the shape the moon appears to us on earth or how much of the illuminated half of the moon we see

• the amount of sunlight reflecting onto the moon and the angle we see it from are what represent the different phases

different moon phases

waxing: growing, waning: shrinking

tides

• long period waves that move across the ocean

• high and low tides occur twice per day, in two places

• caused by the gravitational pull of the moon, less so the sun

• because of the size of the moon, the gravitational force of the moon varies at different locations (diagrams in slides)

spring tides

occur when sun, earth, and moon are in alignment, creates extra large tides

neap tides

occur when sun and moon are at right angles to each other, creates medium tides

aurora

• a natural electrical atmospheric phenomenon

  • northern: aurora borealis

  • southern: aurora australis

how do auroras occur

• solar wind is ejecting from the corona (sun's outer core) onto the ionosphere, sending charged particles towards the poles

• this energy is transformed into light energy, and the chemical composition of the particles depends on the color it emits

• green: oxygen, pink/dark red: nitrogen, blue/purple: hydrogen

sun facts: mass

1,988,500 x 10^24 kg (333,000 earths)

sun facts: volume

1,412,000 x 10^12 km^3 (1,304,000 earths)

sun facts: ellipticity

0.0005

earths orbit: average distance from sun

149.6 x 10^6 km

time it takes for sun to make complete trip around the milky way

230 million years

solar wind

charged particles ejected from the sun's corona

solar cycle

11 year period of solar activity

path of totality

the trail the umbra makes across the surface of the earth

solar eclipse: total

moon completely covers sun (need to be in path of totality to see this)

solar eclipse: partial

moon partially covers sun, only penumbra is cast

solar eclipse: annular

moon's disk is not big enough to cover sun

solar eclipse: hybrid

changes from an annular to a total solar eclipse, and/or vice versa, along the eclipse's path.

why is there not a solar eclipse every month?

the moon's ecliptic is tilted 5 degrees off from earth's, meaning the moon has to touch the earth's ecliptic and be between the sun and earth for a solar eclipse to occur.

lunar eclipse: total

earth's umbra completely covers the moon

lunar eclipse: partial

earth's umbral shadow partially completely covers the moon

lunar eclipse: penumbral

penumbral shadow is cast on moon

eccentricity of moon's orbit around earth

0.0549

how long does it take for the moon to complete one period around earth?

27.3 days

the line separating the day and night side of the moon

terminator