Astronomy Test #4
What observation of Tycho Brahe caused him to doubt Aristotle?
"new star" in 1572(supernova) = heavens are not unchanging and since it did not exhibit parallax he knew this new star could not be near Earth.
Name three ways you could measure and angle of 30 degrees with your hand?
(Pinky = 1) (Three fingers = 5) (Fist = 10) (Pinky + Forefinger = 15) (Pinky + thumb = 25) so 30 pinkies, 6 three fingers or 3 fists
How far from Earth is the moon?
238,900 Miles
2 Astronauts are dropped on a planet 1500 km apart, north-south of each other. At local noon, one astronaut sees the sun at her zenith while the other sees the sun 15 degrees south of his zenith on the meridian. What is the circumference of this planet?
360/15 * 1500 km = 36,000 km
How far from Earth is the sun?
92,000,000 miles or 1 A.U.
Who first proposed a heliocentric theory of the universe?
Aristarchus of Samos
How/Who figured out how to calculate the distance to the moon?
Aristarchus of Samos. Timed movement of moon through Earth's shadow during a lunar eclipse. Also knew the moon and the sun have the same angular diameter as viewed from Earth. This allowed him to construct this triangle and calculate EM distance
Who/How figured out how to calculate the distance to the sun?
Aristarchus of Samos. measured angle between Sun and 1st Quarter moon to be 87 degrees. Used right triangle to calculate ration of EM and ES distance to be 1:20. Modern version of angle is 89.83 degrees so the ratio is 1:400.
How did Copernicus explain retrograde motion?
As an inner planet passes an outer planet the outer planet appears to be moving backwards(like adjacent subway trains)
What is an informal grouping of stars called?
Asterism
What are 3 reasons ancient people studied astronomy?
Clock, Calendar, navigation, Planting/Harvesting, Religious Festivals
Who wrote the book De Revolutionibus Orbium Coelestium(The revolution of the celestial spheres)
Copernicus, a Polish astronomer and Mathematician.
How did Copernicus deduce the order of the planets?
Distance from earth is related to sidereal period.
How did the Greeks know the Earth was round?
Earth's shadow on the moon during a lunar eclipse is round. Ships can be seen coming over the horizon. Sail can be seen before the rest of the ship.
Who had the largest head in the history of astronomy?
Eratosthenes and he was Head Librarian of the Library of Alexandria
Who first determined the circumference of the Earth? How did he do it?
Eratosthenes. He realized that on Summer solstice sun casts a shadow in Alexandria but not Syene. By measuring the length of shadow in Alexandria and using triangles, he determined the angle was 7 degrees which was about 1/50 th of a circle. Since it was 5000 stadia from Alexandria to Syene the circumference of the Earth must be 50*5000 = 250,000 Stadia = 23,650 miles. Modern Measurement is 23,906 miles.
Why did Aristarchus' measurement of the size of the sun cause him to become a heliocentrist?
He determined the sun was much bigger than Earth and he figured small should orbit big
What are some things Galileo saw in his telescope that convinced him that Copernicus was correct?
Jupiter's Moons, phases of Venus, moon craters and mountains, Milky Way, sunspots
How did Copernicus explain why Mercury or Venus are never seen in the middle of the night?
Mercury and Venus are close to the sun and thus can only be seen just before sunrise or after sunset
Why do we always see the same side of the moon?
Moon's rotational period is same as its period of revolution around the Earth. This is due to tidal locking, the tidal bulge is pulled toward Earth
How do you find arc length?
Multiply radius by theta. If theta is an angle multiply it by pi / 180 to get the arc length.
What is the Azimuth of southwest in the horizon coordinate system?
N = 0, E = 90, S = 180, W = 270 SW = 225
What is the altitude of Polaris if you are Standing at the N. Pole, Equator, NYC
N. Pole- 90 degrees Equator - 0 Degrees NYC- 41 Degrees
Why did many astronomers find copernicus' theory more appealing than Ptolmey's even thought it was no more accurate at predicting the location of celestial objects?
Occam's Razor- it was simpler. Epicycles are complicated and unnatural
How did Aristotle describe the heavens?
Perfect, unchanging, move in perfect circles
How does the length of the shadow cast by a vertical stick change throughout the year?
Shortest on Summer Solstice, gets longer until Winter Solstice, shrinks until summer solstice.
At what right ascension coordinate is the summer solstice located? The autumnal equinox?
Summer Solstice - 6 Hours Autumnal Equinox - 12 Hours
Summarize the Tychonic system?
Sun moon and stars revolve around the Earth but the planets revolve around the sun.
What are two reasons that it is colder during the winter?
The northern hemisphere is titled away from the sun during our winter. Sun's rays are least direct and day is shorter. So sun's energy is less concentrated and there is less time for the sun to warm the earth during the day.
What was the major idea of De Revolutionibus Orbium Coelestium?
The sun is the center of the universe
At what time of day (sunrise, 9am, noon, 3pm, sunset, 9pm , midnight or 3am) will thee moon rise/set during the 8 major phases?
Trick new moon with sun, full moon opposite sun 1st time ise 2nd time set New - Sunrise, Sunset Wax Crescent - 9am, 9pm 1st Q - noon, midnight Wax Gibb - 3pm, 3am Full - 6pm, 6am Wan Gibb - 9pm, 9am 3rd Q - midnight, noon Wan Cresc - 3am, 3pm
How did Ptolmey explain retrograde motion?
Using Epicycles, Deferents
Why was Tycho's quadrant so precise?
Very large so it could be divided to very small angeles (1/15) of a degree
Which way does the sun move relative to the background stars?
West to East
Which way do the planets move relative to the background stars?
West to East usually but during retrograde motion East to West
What is the point called directly above you on a horizon diagram?
Zenith