Lecture 2 Flashcards
How is Earth moving in our Solar System
Contrary to our perception, we are not “sitting still”
We are moving with Earth in several ways, and at surprisingly fast speeds.
Earth rotates around its axis
Once every day
Earth orbits Sun(revolves)
Once every year
What direction does Earth orbit
It rotates in the same direction it orbits, counterclockwise as viewed from above the North Pole
How is our Sun moving in the Milky Way Galaxy?
Our sun moves randomly relative to the other stars in the local solar neighbourhood
Typical relative speed of more than 70,000km/hr(20km/s)
But stars are so far away that we cannot easily notice their motion
How do galaxies move within the Universe?
Galaxies are carried along with the expansion of the universe.
How did Hubble figure out that the universe is expanding?
Most galaxies outside our Local Group are moving away from us
The more distant the galaxy, the faster it is receding from us
Basically: We live in a expand Universe
How is Earth moving in our solar system?
It rotates on its axis once a day and orbits
the Sun at a distance of 1 AU = 150million kilometers
How is our solar system moving in the Milky
Way Galaxy?
Stars in the Local Neighborhood move
randomly relative to one another and orbit
the center of the Milky Way in about 230
million years.
How do galaxies move within the universe?
Most galaxies beyond the Local Group
are moving away from us with the
expansion of the universe: the more
distant they are, the faster they’re
moving.
Are we ever sitting still?
No! Earth is constantly in motion, even
though we don’t notice it.
What is Scientific Thinking
Scientific thinking is bases on everyday ideas of observation and trial and error experiments
What did ancient civilizations achieve in astronomy?
Tracking the seasons
Daily timekeeping
Calendar
Monitoring lunar cycles
Monitoring planets and stars
Predicting eclipses
How did Astronomical observations benefit ancient societies?
Keeping track of time and seasons
For practical purposes, including agriculture
For religious and ceremonial purposes
Who could predict seasons?
Ancient people of central Africa (6500 BC) could predict seasons (and therefore how much precipitation they should get under normal conditions) from the orientation of the crescent Moon
The Nebra sky disc
The Nebra sky disc (found near Nebra, Germany) is dated to around 1800-1600 BC. It is the oldest known depiction of astronomical phenomena and contains “golden symbols”
Nebra Disc Golden Symbols for
The sun or full moon
the crescent moon
The pleiades
One angular arc (originally 2 arcs) for the angle between the sunsets at summer and winter solstices near Nebra
Where did most of our mathematical and scientific heritage originated
Civilizations of the Middle East
Why does modern science trace its roots to the Greeks
Greeks were the first people known to make models (or theories) of nature.
They tries to find rational explanations for patterns in nature
How did the Greeks explain planetary motion?
Geocentric
Earth at the center of the universe
Heavens must be “perfect”.
Objects moving on perfect spheres
Ptolemaic Model
Sophisticated geocentric model
Sufficiently accurate
Remain in use for 1,500 years
How did Ptolemaic model explain retrograde motion?
planets really do go backward in this model
Aristarchus of Samos
Proposed a heliocentric model of the solar system. he also made estimates for the sizes and distances of the Sun and the Moon
How did Ptolemy explain planetary motion?
The ptolemaic model had each planet move on a small circle whose center moves around Earth on a larger circle
Nicolaus Copernicus
Proposed a Sun-Centeres model
Use model to determine layout of solar system
The model was no more accurate than the Ptolemaic model in predicting planetary positions, because it still used perfect circles and epicycles
Tycho Brahe
Compiles the most accurate (one arc minute) naked eye measurements ever made if planetary positions
Still could not detect Stellar parallax, and thus still thought Earth must be ar center of solar system (but recognized that other planets go around Sun)
Johannes Kepler
Kepler first tried to match Tycho’s observations with circular orbits
But an 8 -arcminute discrepancy led him eventually to ellipses
What is an ellipse?
An ellipse looks like an elongated circle
Keplers First Law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus
Keplers Second Law
As a planet moves around orbit, it sweeps out equal areas in equal times
This means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun
