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Astronomy 161
Introduction to Solar System Astronomy
Prof. Paul Martini
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Lecture 1: Introduction to Astronomy
An Exciting Time
- Solar System Astronomy (Planetary Science) is in the midst of a
real Renaissance
- Major discoveries in the last decade include:
- Robotic exploration of Mars
- Spacecraft visits to Mercury, Jupiter, and Saturn
- New dwarf planets in the outer solar system
- Dozens of new Solar Systems around other stars
What is Astronomy?
- From the Greek astronomos
- astron = star
- nomos = a system of laws
Today Astronomy means Astrophysics - the study of the physics of
celestial objects, including the study of the Universe as a whole
(Cosmology)
What is Science?
Science is not just a collection of facts, but a process of critical thinking
that leads to understanding the world around us
- Starts with a collection of careful observations
- Provides a framework to understand these empirical data
- This framework can then predict future observations and deepen our
understanding
The Scientific Method
- 1. Gather facts
- 2. Create a hypothesis to explain these facts
- 3. Create a prediction from the hypothesis
- 4. Test this prediction against other facts
Successful? Create new predictions and gather more facts
Unsuccessful? Return to Step 2
What is a Scientific Theory?
Once a hypothesis has been extensively tested and proven to be
predictive, it becomes a Scientific Theory.
- Examples:
- Copernican theory, Theory of Gravity
Scientific theories are purely empirical and in this sense differ from
philosophical theories, which include ideas as well as empirical data
Descriptive Astronomy
- Apparent Motions of the Sun, Moon, and Stars
- The Seasons
- Timekeeping and Calendars
- Phases of the Moon
- Eclipses of the Sun and Moon
- Motions of the Planets
Historical Origins of Astronomy
- Classical Astronomy
- Copernican Revolution
- Copernicus
- Brahe
- Kepler
- Galilei
- Newtonian Synthesis
Physics of Astronomy
- Gravitation
- Newton's Laws
- Orbits and Tides
- Light and Atoms
- Electromagnetic Spectrum
- Atomic Structure
- Interaction of Light and Matter
- Tools of the Astronomer
The Solar System
- The Earth and Moon
- Comparative Planetology
- Terrestrial Planets
- Jovian Planets
- Comets, Asteroids, and the Outer Solar System
- Origin of the Solar System
- Other Solar Systems
Distance in Astronomy
- Size of the Earth
- Diameter: 12,756 km
- Circumference = 40,074 km
- It would take 2.5 weeks driving at 60mph to travel around the Earth
(25,000 miles)
- Earth-Moon Distance
- The Earth is 384,000 km from the Moon
- The distance to the Moon is comparable to how far a very reliable
car will drive in its entire lifetime (240,000 miles)
- Earth-Sun Distance
- The Earth is 1 AU or 149,600,000 km from the Sun
- This is nearly 400 times the Earth-Moon distance or nearly 12,000 times the diameter of the Earth. If you travel 60mph, it would take you 178 years to
reach the Sun.
- Distance from the Sun to the Nearest Star
- Proxima Centauri is 4.22 ly (267,000 AU) from the Sun
Astronomical Units of Length
- Astronomical Unit (AU):
- Mean distance from the Earth to the Sun
- 1 AU = 1.496 x 108 kilometers
- Used for distances between planets
- Light Year (ly):
- Distance traveled by light in 1 Year
- 1 ly = 9.46 x 1012 kilometers
- Used for distances between stars
- Parsec (pc):
- 1 pc = 3.26 ly
- Distance at which 1 AU subtends an angle of 1 arcsecond
See A Note about Graphics to learn
why some of the graphics shown in the lectures are not reproduced with
these notes.
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Updated: 2010 January 3
Copyright © Paul Martini All Rights
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