Chapter 1 - Cosmology & Planets Flashcards
Why is the Earth called “The Pale Blue Dot”?
The Earth outward is blue even though it cannot be recognized as such by us humans since we are too small to look outward from an inward perspective.
Describe the motion of celestial objects
There is order in the movement of celestial objects. Stars in the northern hemisphere can be seen to revolve around the North Star:Polaris. Planets are other objects which move relative to the star movement in a “wandering” motion.
What can help us determine a date (month/day)?
The location of a planet on its wandering path.
What are the approaches that were used to explain the motion of stars and planets?
The geocentric perspective as a Ptolemaic model where the Earth was at the centre and the heliocentric perspective as a Copernicien model where the sun was at the centre.
What is the geocentric perspective?
The geocentric perspective was proposed by Aristotle but challenged by Aristarchus. The geocentric universe was deeply entrenched in church doctrine but simple spheres containing the planets and the sun revolving around the Earth did not explain the retrograde motion of planets.
Where does retrograde motion occur?
Retrograde motion occurs when planetary motion appears to move backwards with respect to the common motion of the system (ie. Mars/Jupiter from Earth)
Who were key figures in the shift towards belief of the heliocentric model?
Ptolemy: proposed that planets also follow a smaller circular orbit called epicycles that pointed out predictable periods of retrograde motion.
Copernicus: came to suggest that because Mars has the largest retrograde motion it is closest to Earth while Saturn having the smallest retrograde motion is furthest from the Earth. He also explained that the rising and setting of the sun was due to the Earth spinning on an axis.
Galilei: invented telescope;observing venus
Kepler: proposed 3 laws:
1. The law of ellipses: the orbit of each planet is an ellipse where the sun is in the centre.
2. The law of orbital harmony: for planets, (the orbital period in years)^2 is proportional to (its average distance from the sun)^3
3. The law of equal areas: relates a planet always has equal areas in equal time in its relation to the sun even though the orbital velocity changes (may be farther away from sun but still has equal area in relation to equal time length wherever it may in its orbit)
What were the time periods that the heliocentric and geocentric perspectives were accepted as “the truth”?
Geocentric perspective was observed in 4th century bce and the heliocentric perspective was accepted in 17th century ce.
Describe our solar system
Our solar system consists of our star; the sun, the planets, their satellites (ie. Earth’s satellite is the moon), and asteroids. Our galaxy is located on the arm of the Milky Way galaxy. Our solar system has inner planets that are terrestrial which mean they have metal cores and a rocky shell, and outer planets which are gas-giants made of H and He.
What is a galaxy
A galaxy is a system of stars held together by gravity
Define a planet
A planet must:
Orbit a star
Be roughly spherical
And have a strong enough gravity pull to clear its neighbourhood of other object
How was the size of the earth determined?
Eratosthenes calculated the circumference of the earth by measuring the shadow at the bottom of two wells 800km apart at the same time (correct within 2%)
Which planet has the lowest/highest density?
Lowest Density: Saturn Uranus Jupiter Neptune Mars Venus Mercury Highest Density: Earth
Sarah’s Urn Joins No Man’s Vase Made by Earth
Smallest to largest planets
Shortest: Mercury Mars Venus Earth Jupiter Neptune Uranus Longest: Saturn
MaaM VEJeeNUS
Describe the makeup (%composition) of our solar system
99.8% = sun
(71% of 2%)0.142% = Jupiter
0.058% = other
