Transcript Astronomy 1010 - The University of Toledo

Lecture 2
The Solar System
The Universal Gravitation
Chapter 1.3  1.11
Homework: On-line quiz for Chapter 1 (due August 27th)
Outline
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What we see in the sky
The Ptolemaic system
The Copernican system, Kepler’s laws
Universal gravitation
Constellations
• Patterns of stars seen in the sky
• There are 88 constellations
• About 50 of them were named by ancient
Greeks and Romans
Constellation of Orion
Winter triangle
Daily star paths
Seasonal changes in the sky
Annual change of the Sun altitude
Ancient Observations
• Relations of celestial objects to weather and
agriculture
• Observations of the Sun and Moon
• Observations of stars and planets
Ptolemaic model of the Universe
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
Ptolemy (A.D. 100  170)
Ptolemaic Epicycles
The Ptolemaic model along with a catalog of
positions of 1028 stars were published in his book
Almagest
Nicolaus Copernicus (14731543)
Copernicus is said to be the founder of modern
astronomy
Kepler’s Laws
1. Planets move on elliptical orbits
2. The planet’s radius-vector sweeps out the
same areas in equal times
3. The squares of the periods of the planets are
proportional to the cubes of their semimajor axes
Demonstration of Kepler's laws
The Solar System
• Content:
Sun (the only star)
9 planets
Nearly 100 moons
Asteroids
Comets
Free-flying gas and ``dusty’’ particles
http://solarviews.com/eng/homepage.htm
Planets of the Solar System
Object
Mercury
Diameter
Dist. from Sun
Dist. in A.U.
Revol. Period
Earth years
4,880
57.9 million km
0.4
0.2
Venus
12,100
108.2
0.7
0.6
Earth
12,760
149.6 (1 A.U.)
1.0
1.0
Mars
6,790
227.9
1.5
1.9
Jupiter
143,000
778.3
5.2
11.9
Saturn
120,000
1,427
9.5
29.5
Uranus
52,000
2,870
19.2
84.0
Neptune
48,400
4,497
30.1
164.8
2,260
5,900
39.4
247.7
Pluto
Sir Isaac Newton (1642-1727)
The Universal Law of Gravitation
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
gravity
The Universal Law of Gravitation
Support of Kepler’s Laws
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
Tides are due to gravitational attraction between
the Earth and the Moon
Spring Tides
Neap Tides
Tidal Friction and Synchronous Rotation
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)
The Discovery of Neptune
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.
Urbain Leverrier (18111877)
Astronomy and Astrology
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
Summary
• The Earth is not the center of the universe but instead is a
planet orbiting a rather ordinary star in the Milky Way
Galaxy.
• Celestial bodies in the gravitational field of each other
move according to Kepler’s laws.
• Newton’s discoveries showed that the same physical laws
we observe on Earth apply throughout the Universe.