Lecture 2 The Solar System The Universal Gravitation. Chapter 1.3 1.11. Homework: On-line quiz for Chapter 1 (due August 27th). Outline. What we see in the sky The Ptolemaic system The Copernican system, Kepler’s laws Universal gravitation. Patterns of stars seen in the sky
Chapter 1.3 1.11
Homework: On-line quiz for Chapter 1 (due August 27th)
Patterns of stars seen in the sky
There are 88 constellations
About 50 of them were named by ancient Greeks and Romans
Relations of celestial objects to weather and agriculture
Observations of the Sun and Moon
Observations of stars and planets
Developed by Claudius Ptolemy (A.D. 100-170)
The Earth is in the center
The Sun is at the third orbit from Earth after Mercury and Venus
Epicycles are added to circular orbits of planets to explain retrograde motion
The Ptolemaic model along with a catalog of positions of 1028 stars were published in his book Almagest
Copernicus is said to be the founder of modern astronomy
Demonstration of Kepler's laws
Sun (the only star)
Nearly 100 moons
Free-flying gas and ``dusty’’ particles
Every mass attracts every other mass through the force called gravity
The force of attraction is directly proportional to the product of their masses
The force of attraction is inversely proportional to the distance between the objects
Fg = G x M1x M2 / d2
Newton found that Kepler’s first two laws apply not only to planets, but to any object going around another one under the force of gravity
The orbits do not have to be elliptical
They can also be parabolic or hyperbolic
Tides are due to gravitational attraction between the Earth and the Moon
The tidal bulges try to stay on the Earth – Moon line
The Earth’s rotation tries to pull the bulges around
The tidal friction slows down the Earth’s rotation
The length of a day gets longer
It makes the Moon move further away from Earth
The Moon is in synchronous rotation with the Earth
(always showing the same face)
In 1781, the planet Uranus was discovered telescopically
from Britain by William Herschel.
In 1845, a Cambridge mathematician, John Couch Adams, based on the law of gravitation, predicted the existence of an unseen planet, to account for the fact that Uranus was being pulled slightly out of position in its orbit.
He sent the calculations to test to England’s Royal Astronomer, who set them aside.
Shortly after that, a French mathematician, Urbain Leverrier,published a similar prediction and contacted astronomers at Berlin Observatory, who found the new planet on the night of 23 September 1846.
Astronomy is a science
It describes the real world, sets new problems and solves them, using methods of itself and other sciences (such as physics and mathematics)
Astrology is interpreting apparent positions of the Sun, planets, and stars to predict human life.
It does not set and solve any problem
The Earth is not the center of the universe but instead is a planet orbiting a rather ordinary star in the Milky Way Galaxy.