The Birth of Modern Astronomy Flashcards
What was so mysterious about planetary moton in our sky to early astronomers?
Like the Sun and Moon, planets usually drif
eastward relatve to the stars from night to night; but sometmes, for a few weeks or few months, a planet turns
westward in its apparent retrograde moton
Why did the ancient Greeks reject the real explanaton for planetary moton?
Most Greeks concluded that Earth
must be statonary, because they thought the stars could not be so far away as to make parallax undetectable
How did Copernicus, Tycho and Kepler challenge the Earth-centered idea?
Copernicus created a sun-centered
model; Tycho provided the data needed to improve this model; Kepler found a model that ft Tycho’s data
Which astronomers challenged the Earth-centered idea?
Copernicus, Tycho and Kepler
How did Copernicus, Tycho and Kepler challenge the Earth-centered idea?
Copernicus created a sun-centered
model; Tycho provided the data needed to improve this model Kepler found a model that ft Tycho’s data
What was Galileo’s role in solidifying the Copernican revoluton?
His experiments and observatons overcame the remaining objectons to the Sun-centered solar system. (Tycho’s observatons of comet and supernova already challenged this idea.)
Using his telescope, Galileo saw:
- Sunspots on Sun (“imperfectons”)
- Mountains and valleys on the Moon (proving it is not a perfect sphere)
Who invented telescopes and thermometers?
Galileo
Who discovered Moon’s craters, Jupiter’s moons, phases of Venus, and stars in Milky Way?
Galileo
Kepler’s 1st law of planetary motion
- The orbit of each planet is an ellipse with the Sun at one focus
Kepler’s 2nd law of planetary motion
- As a planet moves around its orbit it sweeps our equal areas in equal tmes
Kepler’s 3rd law of planetary motion
- More distant planets orbit the Sun at slower average speeds: p^2 = a^3
p = orbital period in years
a = avg. distance from Sun in AU
Does 3-rd Kepler’s law depends on masses of planets?
No
Will a small rock and a big planet have the same period of rotaton if they happen to be at the same distance to the Sun?
Yes
Which planet is the fastest in a solar system - Mercury, Venus Mars, Jupiter? Which Kepler’s law explains it?
Mercury (Kepler’s 3rd law)
What did Copernicus conclude?
Copernicus concluded that Earth is a planet and that all the planets circle the Sun. Only the Moon orbits Earth
What did Copernicus conclude?
Copernicus argued that the apparent motion of the Sun about Earth during the course of a year could be represented equally well by a motion of Earth about the Sun.
Could Copernicus prove that Earth revolves about the Sun?
no
Why, in Copernicus’s time there was little motivation to carry out observations or experiments to distinguish between competing cosmological theories
In Copernicus’ time, in fact, few people thought there were ways to prove whether the heliocentric or the older geocentric system was correct. A long philosophical tradition, going back to the Greeks and defended by the Catholic Church, held that pure human thought combined with divine revelation represented the path to truth.
Who showed that rest is no more natural than motion.
Galileo
accelerate
—change their speed or direction of motion.
Galileo’s Astronomical Observations about jupiter
- Galileo found four moons revolving about Jupiter in times ranging from just under 2 days to about 17 days. This discovery was particularly important because it showed that not everything has to revolve around Earth.
- Within a few months, he had found that Venus goes through phases like the Moon, showing that it must revolve about the Sun,
Meridian
a half-circle extending from your horizon due north, through your zenith, to your horizon due south
What is a circumpolar star?
a star that always remains above your horizon
You are standing on Earth’s equator. Which way is Polaris, the North star?
on the northern horizon
Orion is visible on winter evenings but not summer evenings because of
the location of Earth in its orbit.
He discovered that Jupiter has moons.
Galileo
Kepler’s third law, p2 = a3, means that
all orbits with the same semi-major axis have the same period.
the period of a planet does not depend on its mass.
a planet’s period does not depend on the eccentricity of its orbit.
planets that are farther from the Sun move at slower average speeds than nearer planets.
From Kepler’s third law, a hypothetical planet that is twice as far from the Sun as Earth should have a period of
more than 2 Earth years.
Kepler’s second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, means that
a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.
