Earth and Moon Flashcards
What is the mean distance that the Earth and Moon orbit the sun.
149 million km (1 Astronomical Unit)
365.256 days (1 year) to complete an orbit
What size is Earth compared to the moon?
81 times more massive and 4 times radius
How many days does it take the moon to orbit the Earth and what is the mean distance? (sidereal period)
27.3 days, mean distance of 384000 km.
Define the sidereal period?
time taken to complete an orbit with respect to the fixed distant stars
Why does the separation of the moon to the earth vary from 362000-405000 km?
the orbit is elliptical
what else does the moon do every 27.3 days?
rotates on its axis- to keep same face towards us
How much does the planes of the Earths orbit around the sun and the moons orbit around the earth differ by?
5 degrees
what is the Earths spin axis inclined at and what effect does this have on the moon?
23.4 degrees
moon reaches diff heights in the night sky at diff times of the year
when is the new moon visible?
never- moon is same direction as sun
when is crescent visible?
west after sunset or in east before sunrise
when is the first quarter visible and when does it rise?
rises at midday, sets at midnight
visible in evening as half phase.
moon 90 degree away from sun
when is the full moon visible?
throughout night
when does full moon rise and set?
rises at sunset
sets at sunrise
how far away from the sun in degrees is a full moon?
180
When is the last quarter moon visible?
in morning as half phase
when does last quarter rise and set?
rise at midnight, sets at midday
how far away from the sun in degrees is a last quarter moon?
90
how many days does a complete lunar phase take and why?
29.5 days because as moon orbits earth, position of sun changes
what is a solar eclipse?
moon passes in front of sun, blocking light from part or all of sun reaching earth.
when can a solar eclipse occur?
new moon
what is a annular solar eclipse and when does it occur?
sun appears as ring (annulus) moon too small to cover sun
what is a lunar eclipse?
moon enters earth shadow cone preventing sunlight reaching moon, Moon turns coppery red, due to sunlight refracted through earths atmosphere.
where is a lunar eclipse visible?
anywhere on earth where moon is visible above horizon.
when can a lunar eclipse happen?
full moon
why dont we have eclipses every month?
because orbit of the moon about the earth is tilted with respected to that of the sun
what is a tide?
gravitational force due to a distant object decreases with distance from the object. Body is subjected to stronger pull on side closest to object .
what is the difference of gravitational force known as?
tidal force
what is the equation for tidal force?
Ftidal = 2RGM/d^3 F tidal= tidal force per unit R= body of radius M= another body of mass d= distance
why does the earth not stretch very much?
moons tidal force
rigid
why is earths oceans strongly influenced by moons tidal force?
oceans are liquid and water can flow when force applied to it
how are two tidal bulges formed?
the tidal force has a stretching effect along a line between Earth and Moon
why does the tidal bulge move around the surface of the earth?
due to earths rotation
why does Earths surface experience two high tides and two low tides per day?
bulge generally aligned toward and away from moon
what is a spring tide and why does it occur?
when sun and moon are aligned (new moon, full moon) tidal forces of sun and moon add together .
what is Neap tides and why do they occur?
when sun and moon are perpendicular to each other. (first quarter, last quarter)
what is tidal friction?
when frictional forces occur between water and land causing a lag in ocean bulge which has breaking effect on earths rotation.
What effect does tidal friction have?
extracting energy from earth-moon system and expending it as head, Length of day increasing by 1.7 milli-seconds per century and earthmoon separation increasing 3.8cm/year
how much more greater does the moon experience tidal force due to the earth than the earth due to the moon? what does this mean?
20x
moon slightly elongates along line towards earth and moon rotation rate reduced by tidal forces until equalled orbital period
