Transcript Astronomy - GEOCITIES.ws

Astronomy
• Oldest “Science”
• Observed patterns and regularities between events
on Earth and the position of heavenly bodies
– recorded data about the heavenly bodies started with
earliest written records
• Could use patterns to make predictions
– What sort of observed patterns could lead to useful
predictions?
• seasons and position of the sun
• Equinoxes, length of days
Greek Astronomy (600 BC- AD 150)
• Much of their arguments were non-science.
• Used geometry and trigonometry to measure sizes
and distances of sun and moon.
• Geocentric (Earth Centered).
– Phases of the moon understood if moon is a sphere
shining with reflected light
– Eclipses understood if Moon passes by Earth’s shadow
– Spherical Earth understood
• Earth cast curved shadow during lunar eclipse
– Heavens misunderstood
• Rotating celestial sphere.
Greek Astronomy (600 BC- AD 150)
• Found circumference of the Earth.
– Used difference in the angles of sun’s shadow
at two locations, distance between the locations,
and assumption of spherical Earth.
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Only one cast a shadow
Angle = 7 degrees (1/50 of a circle).
D = 31726 km between cities
50 x 31726 km= 39,400 km for the whole circle.
(actual Earth circumference = 40,075 km).
Greek Astronomy (600 BC- AD 150)
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Only one cast a shadow.
7 degrees = (1/50 of a circle).
5000 stadia (1 stadia /0.1576 km) = 31726 km.
50 x 31726 km= 39,400 km for the whole circle.
(actual = 40,075 km).
Greek Astronomy (600 BC- AD 150)
• Heliocentric (Sun Centered).
– Suggested 200 BC, but didn’t catch on
• indirect measurement was used to calculate size of
Sun and Moon.
• Found the Sun is much larger than the Earth, much
farther away than the Moon.
• If Sun is so much bigger, and farther away, wouldn’t
it make sense that the Earth would revolve around it,
rather than vice versa?
Greek Astronomy (600 BC- AD 150)
• Ptolemaic System (Geocentric).
– The most generally accepted theory
– All heavenly bodies revolve around Earth
– Accounted for retrograde motion by Spirograph
method
– Similar to passing a car
Modern Astronomy : Authors
• Nicholas Copernicus (1473-1543). Heliocentric.
– First “modern” astronomer to be proponent of the
heliocentric model
– Earth is a planet, therefore should behave like other
planets. Doesn’t make sense it is the center.
– Used circular orbits, which still didn’t quite fit
observations.
– Work was published on is deathbed, so he didn’t suffer
the consequences of social ostracism.
Modern Astronomy: Authors
• Tycho Brahe (1546-1601) Geocentric
– Headed a Danish observatory.
– Very precise measurements of Mars and other
heavenly bodies.
– Not heliocentric because he didn’t see stellar
parallax
– Change in position of stars relative to Earth’s position in
revolving around the sun
– Like closing one eye and pointing to a distant object, then
switching eyes without moving your finger.
Modern Astronomy: Authors
• Johannes Kepler (1571-1630) Heliocentric.
– Tycho’s assistant.
• Used Tycho’s data to prove heliocentric model better.
• Mars orbit is elliptical.
– 3 Laws of Planetary Motion.
• Path of each planet is an ellipse with the Sun as one focus.
• Revolution carves out equal areas in equal amount of time.
• Orbital periods of the planets and their distances from the Sun
are proportional (p2=d3).
– Did not determine the forces that produce the planetary motion.
Modern Astronomy: Authors
• Galileo Galilei (1564-1642) Heliocentric.
– First to make and use telescopes in astronomy.
• Found 4 moons orbiting Jupiter.
– Therefore Earth not the center of revolution for everything! And
moons not left behind as Jupiter revolved around the Sun.
• Planets are circular discs, not points of light.
• Venus has phases, like the Moon, so the sun is the center of it’s
revolution.
– Venus is smallest in full phase.
• Moons surface has landforms.
• Sun has sunspots, and it rotates.
– Tried by the Inquisition, convicted, imprisoned, became
blind.
Modern Astronomy: Authors
• Sir Isaac Newton (1642-1727).
– Universal Law of Gravitation
• Every body attracts every other body with a force proportional
to their masses and inversely proportional to the square of the
distances between them.
– 3 Laws of Motion
• Inertia: An object in motion continues moving at uniform
speed in a straight line unless an outside force acts on it
• F=ma
• Every force (action) has and equal and opposite force
(reaction)
Gravity
• Gravity increases with increasing mass
• Gravity decreases with distance
• Fg = G m1m2/d2
• Where G=6.67x10-11 Nm2/kg2
• (Small enough to ignore)
Mass and Weight
• MASS is how much matter an object has
– how many atoms and what kind of atoms
• some atoms have more mass because they have more protons
and neutrons
– Mass doesn’t change from one place to another
• WEIGHT is the acceleration due to gravity acting
on a mass
– Weight is actually a force (F=ma; mass being
accelerated)
– Gravity will differ based on the mass of the planet, so
weight can change. You can be “weightless”, but not
“massless”