Lecture 5 Flashcards
describe a solar eclipse
when the moon is b/w the earth and sun
moon blocks light from the sun which casts a shadow on earth
what are the 2 parts of the shadow in a solar eclipse?
penumbra: lighter part
umbra: darker part
why don’t we have eclipses more often?
b/c moon’s orbital plane is t ilted by 5 deg w/ respect to the ecliptic
can have eclipses only twice per year
why are lunar eclipses more common than solar?
the moon’s shadow on earth is much smaller than the earths shadow on the moon
total solar eclipses can only seen on some parts of the earth
___ side of the moon always faces the earth
a) same
b) difference
same
what causes tides on earth?
b/c of gravitational force due to moon on on side of earth greater than on other
when the moon is further away, tides are weaker
why is there an offset of tidal bulges? what does this cause?
tidal bulges don’t point directly at the moon b/c of the earth’s rotation
thus it is 10 degrees off
causes the moon to be pulled ahead in its orbit –> gives E –> spirals outward slowly –> earth/moon distance increases by 3.8cm each year
how can you tell that the moon/earth distance is changing?
can bounce radio waves off moon and see how long it takes for it to return
what is spring tide?
the largest tide b/c friction b/w earth and oceans makes the earth rotate more slowly
sun in line with earth and moon
at a new and full moon
what is the neap tide?
smallest tide
sun at right angle to earth/moon line
describe the moon tide
what does this cause?
moon also feels a similar tidal force
but them moon is solid, so the effect is not as pronounced as on earth
can be seen as tide-correlated moonquakes
tide cased a raised bulge in the moon which forces the moon to rotate synchronously. The bulge is alwasy pointing toward to earth
what is stellar parallax?
why is it imp?
technique to measure astronomical distance
aka triangulation
very imp because the viewing angle changes the background. The earth’s position in january is different than in june, thus the location of the star will look different
what is 1 arcminute?
what is 1 arcseccond?
1 degree (out of 360) is 60 ‘ (arcmin)
1’ = 60’’ (arcseconds)
