A1 - Earth Flashcards
What shape is the Earth?
oblate spheroid (wider at equator)
Where is the prime meridian?
0° longitude, goes through Greenwich
Where is the International Date Line?
180°E/W, serves as a boundary between 1 calendar day and the next
Which direction does longitude increase in?
going East
When are the equinoxes?
21st of March and September
Describe the motion of the Sun at the Equinoxes:
the Sun rises exactly in the East and sets exactly in the West
It follows the Celestial Equator, which makes the day/night exactly 12 hours each
What happens at the Tropics during Summer (Winter) Solstice, and when is it?
-21st June (December)
-Tropic of Cancer (Capricorn) has Sun at zenith, because Earth is tilting towards (away from) it
Describe the motion of the Sun during the Summer Solstice on the Tropic of Cancer:
-the Sun rises in the East
-it passes through the zenith at noon
-sets in the West
Explain why it is called the Tropic of Cancer:
-the Sun used to be in Cancer during the Summer Solstice but it isn’t anymore
-axial precession caused the stars to move relative to the highest point on the ecliptic (+23.5° dec.)
Always say the last point about how the stars move, but relative to the ecliptic
What defines the Arctic/Antarctic circles?
-the latitude that has tangential sun rays during the solstices
-this either gives the Arctic/Antarctic 24hrs of day or night
How does the hours of sunlight received change with latitude over the course of a year?
-higher latitudes will have a larger variation in daylight hours over the course of a year (with the most extreme being the North Pole, which gets 24hrs of day in Summer, to 24hrs of night in Winter)
-there is little variance as you go closer to the Equator
Why is the sky blue in the day?
-Rayleigh scattering
-molecules in upper atmosphere scatter higher frequency waves more (blue waves)
-results in sky being cast with a blue colour
only happens in upper atm. because of the lower density
What makes the sky more orange at sunset/sunrise?
-the blue light gets scattered away from the Earth because there is more atmosphere in the way at sunset/sunrise
-reddish colours scatter less and thus get cast onto the sky
What does light pollution cast into the sky? What affect does it have on observations?
-light scatters and forms a dome around city
-makes it harder to see dimmer stars, because it lowers the contrast between the star and the background of the sky, so fewer objects are visible
-also makes the colour more dull and faint
What is the difference between seeing conditions and the weather?
-seeing is a measure of how still a star/object will appear to be due to atmospheric turbulence
-weather affects the transparency of the sky, and can obscure it with clouds
Why do planets not twinkle in the sky?
-planet’s reflected light is from a disk (subtends a larger angle in sky) rather than a point source because it is much closer
-little patches on the planet’s disk vary in brightness from twinkling but the overall effect gets cancelled out so it doesn’t twinkle (only very slightly)
