Units of MeasureUnits of Measure

Earth diameterEarth diameter12,800 Km12,800 Km

Astronomical Astronomical Unit – Unit – avg. distance avg. distance between Earth/Sunbetween Earth/Sun

150,000,000 150,000,000 KmKm

1 AU1 AU

Speed of Light Speed of Light (c)(c)

300,000 300,000 Km/secKm/sec

Light yearLight year 9.5 x 109.5 x 101212 Km Km 6.3 x 106.3 x 1044 AU AU

Earth-Moon SizesEarth-Moon Sizes

 EarthEarth – Radius is 6,378 KmRadius is 6,378 Km

 Using earth as 1Using earth as 1

 MoonMoon

– Radius is 1,738 Km Radius is 1,738 Km

 0.27 0.27

 ~1/4 radius~1/4 radius

Earth-Moon SizesEarth-Moon Sizes

 If the Earth were this ball, which of the If the Earth were this ball, which of the others could be the Moon? others could be the Moon?

 

– This ball (Earth) ~ 16 cm This ball (Earth) ~ 16 cm

– Therefore Moon ~ 4 cmTherefore Moon ~ 4 cm

Earth – Moon SystemEarth – Moon System

 How far away from Earth is the Moon? How far away from Earth is the Moon?

 

 Take our model Earth and Moon and Take our model Earth and Moon and place them the distance away you think place them the distance away you think they should be…they should be…

Earth – Moon DistanceEarth – Moon Distance

 Distance from Earth to Moon Distance from Earth to Moon – 384,400 Km 384,400 Km – ~30 x Earth’s diameter ~30 x Earth’s diameter

 Using our objects? Using our objects? – If Earth is ~ 16 cm If Earth is ~ 16 cm – Distance (30 x 16cm) ~ 480 cm (5 m)Distance (30 x 16cm) ~ 480 cm (5 m)

Sun – Earth SystemSun – Earth System

 How does the size of the Earth compare How does the size of the Earth compare to the Sun? to the Sun?

 

 If this was our Earth, how big would the If this was our Earth, how big would the Sun be?Sun be?

Sun – Earth SizesSun – Earth Sizes

Earth Radius Earth Radius 6378 Km6378 Km

Using Earth as 1 Using Earth as 1

If Earth is 16 cmIf Earth is 16 cm

Sun Radius Sun Radius 6.96 x 106.96 x 1055 Km Km (696,000 Km) (696,000 Km)

~109x Earth ~109x Earth ~ 2x Earth-Moon ~ 2x Earth-Moon distance distance The Sun 17 m The Sun 17 m diameter diameter

Sun – Earth DistanceSun – Earth Distance

 Distance from Earth to Sun Distance from Earth to Sun

1.5 x 101.5 x 1088 Km (150,000,000 Km) Km (150,000,000 Km)

~400 x Earth-Moon distance ~400 x Earth-Moon distance

or 8.33 light minutesor 8.33 light minutes

Sun – Earth DistanceSun – Earth Distance

 How far away from the Sun is the Earth? How far away from the Sun is the Earth?

 

 Using our model Earth, how far do you Using our model Earth, how far do you think the Sun is? think the Sun is? – Earth is 16 cm Earth is 16 cm – About 2 Km from Sun to Earth About 2 Km from Sun to Earth – About the distance to Westville in New Haven About the distance to Westville in New Haven

Earth’s MotionsEarth’s Motions

Orbital direction – revolves around the Orbital direction – revolves around the sun counterclockwise sun counterclockwise

 Orbital period – 365.26 days Orbital period – 365.26 days

Rotational period – 1 day Rotational period – 1 day

Tilt of rotation – 23.5 degreesTilt of rotation – 23.5 degrees

Earth’s rotation

Earth rotates (spins) on its axis about 1700 km/hr (at the equator) and almost 0 km/hr at the poles.

Evidence for Earth’s rotation:1.Foucault’s pendulum

• 2. Coriolis Effect- air and water are deflected to the right in the northern hemisphere and to the left in the southern hemisphere due to earth’s rotation

• video here

• 3. Star trails

Moon’s MotionsMoon’s Motions

 Orbital direction – counterclockwise Orbital direction – counterclockwise

 Tilt of orbit – approx. 5 degrees Tilt of orbit – approx. 5 degrees

 Orbital period – 27.3 days (sidereal Orbital period – 27.3 days (sidereal month)month)

 Rotational period – 27.3 days Rotational period – 27.3 days

 Synchronous rotation-Synchronous rotation-

moon’s rotation equalsmoon’s rotation equals

its revolutionits revolution

TidesTides

• Influenced by Moon (and Sun)– Moon’s gravity pulls up water on side of Earth

facing it– Another high tide occurs on opposite side of

Earth

• 2 high tides and 2 low tides each day

• Moon rises and sets 50 minutes later each day, so tides occur about 50 minutes later each day

TidesTides

Earth’s SeasonsEarth’s Seasons• Caused by Earth’s tilted axis (23.5°)

and its orbit (revolution) around the sun

• Earth’s orbit is an ellipse; Earth is actually closest to the sun during our winter (rather than our summer) – Perihelion- occurs when Earth is closest to

sun (in January)– Aphelion- occurs when Earth is farthest

from the sun (in July)

Video links

Earth’s rotation (day) and revolution (year)

Tides

EquinoxesEquinoxes

• Autumnal (Fall) / Vernal (Spring) Equinoxes- Sun is directly overhead at the equator; equal hours of night and day– Both hemispheres have equal hours of

day/night

Spring/Fall Equinoxes

SolsticesSolsticesSummer solstice (June 21)-

•Northern Hemisphere leans towards sun•Northern hemisphere has maximum daylight hours•Sun is directly overhead at the Tropic of Cancer (23.5°N)

Summer Solstice

Winter Solstice

Solstices cont’d…..Solstices cont’d…..

Winter Solstice (December 21)• Southern hemisphere is tilted

towards the sun (Northern hemisphere leans away)

• Northern hemisphere has least daylight hours

• Sun is overhead at Tropic of Capricorn (23.5°S)

Angle of Sunlight (or Angle of Sunlight (or Insolation)Insolation)

• Insolation- the amount of incoming solar radiation

• Angle of light affects temperature

• Sun is higher in the sky during summer; energy is more concentrated and shadows are short

• Sun is lower in the sky during winter; energy strikes ground at a slant and is more spread out; less concentrated; longer shadows