our place in the cosmos and introduction to astrophysics jon loveday astronomy centre department of...
TRANSCRIPT
Our Place in the Cosmosand
Introduction to Astrophysics
Jon LovedayAstronomy Centre
Department of Physics & Astronomy
Course Aims
To explain primarily at a descriptive level the contents, dimensions and history of the Universe, and our place within it. This will include a survey of the basic astronomical tools, and will seek to explain the way in which some basic physical laws can be applied in order to understand the observed phenomena.
Class organisation
Lectures Monday 9am Arts A5 Friday 9am Pev1 1A6
Workshops Friday 10am Our Place in the Cosmos: Pev1-2A2
Informal discussion, quizzes, student presentations
Intro to Astrophysics: Arundel 1B Mathematical background, problem sheets Taken by Peter Thomas
Assessment
Our Place in the Cosmos 15 minute presentation (weeks 5-10; 20%)
In-class quiz (week 10; 20%)
2000-word essay (week 10; 60%)
Introduction to Astrophysics 4 x problem sheets (10% each)
In-class quiz (week 9; 40%)
Briefing paper (week 9; 20%)
Web Resources
Sussex Direct has links to the official course document (click on the course code: F3095 or F3156)
Study Direct includes copies of these slides and other useful resources
Course textbooks
21st Century Astronomy by Hester et al. is very good, though expensive at £42
Introductory Astronomy by Holliday is cheaper
Other useful books you should find in the library include: Universe Freedman & Kaufmann In Quest of the Universe Kuhn & Koupelis
Student Feedback
Please feel free to stop me and ask for clarification at any time during classes if anything I have said is unclear
Feedback on any aspect of the course is welcome during the Friday seminar
Formal feedback will be requested via the Study Direct website during weeks 8-9. Please note that feedback provided in this way is completely anonymous
What is Astronomy?
Literally means “naming the stars” The earliest astronomers simply tracked the motions of the heavenly bodies
Modern astronomers use observations to help understand the Universe and our place within it via scientific reasoning
Astrology is not astronomy, but a pseudo-science
Why Astrology is not a Science
The constellations are only imaginary, not physical associations of stars
Constellations have shifted relative to our calendar due to precession of equinoxes since founding of astrology
Rigorous tests of astrological “predictions” have shown they do not work
The Scientific Method
Guided by observations, posit a theory that explains them
A good theory makes testable predictions about future observations, and thus is falsifiable
Scientific theories can never be definitively proved, they can only be ruled out by contrary observations
A theory that stands the test of time becomes generally accepted and possibly modified
Why Study Astronomy?
Early astronomers used positions of the stars to track the seasons and later as a vital navigational aid
Help understand phenomena such as tides and eclipses
Understand and appreciate even more the beauty of the night sky
Learn about the origin and fate of the Universe
Course Outline
Brief tour - scales in the Universe Historical overview Earth, Moon and Sun Orbits and Gravity Solar System Stars Galaxies The Milky Way The Universe
A brief tour
Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Solar System
Milky Way
Milky Way as Viewed from Earth
NGC 891
Milky Way in the near-IR
NGC 4414
A cluster of galaxiesVirgo Galaxy Cluster
Infrared Universe
The Deep Universe Hubble Ultra-Deep Field
CMB Temperature Map
Scales in the Universe
Astronomical distances are commonly given in terms of light travel time, ie. distance light will travel in that time at its speed of 300,000 km/s
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Distances as light travel times - not to scale!
Prehistoric astronomy
Since prehistoric times, man has observed the changing phases of the moon during the lunar month, and the changing passage of the Sun during the year
One can understand how, as well as indicating the change of the seasons, man might well have thought of the stars as causing the change
Hence religious significance of the heavenly bodies, and birth of astrology
Dots below horses thought to represent changing phasesof the Moon
Earliest depictions of the skies are found in the Cave paintings in Lascaux, SW France (c15,000 BC)
The Great Bull: An Ice Age Star Map?
Pleiades
Hyades
Orion
Prehistoric astronomy
Observations of the changing passage of the Sun and the star patterns in the night sky enabled tracking of the seasons, and hence the best times to plant and harvest crops
Observations of the Moon’s phase allowed fishermen to predict the tides
Observatories were built to track the positions of the heavenly bodies, most famously Stonehenge, 3000-1500 BC
Stonehenge
An early astronomical calculator? On summer solstice, Sun rises exactly above the Heelstone
In Stonehenge Decoded (1965), Gerald Hawkins claimed large number of alignments with Lunar and Solar phenomena, and hence that eclipses could be predicted
These claims are still controversial
At sunset close to the spring and autumn equinoxes, shadows give the effect of a snake slithering down the stairway.
El Castillo, Chichen Itza (Mayan, c1000 AD)
The Planets
It must have been noticed very early that some bodies moved faster in the night sky than the surrounding stars.
The word "planet" comes from the Greek word "planetes," which means "nomad” or “wanderer”.
To the Babylonians and Sumerians before them, the planets were "stray sheep”.
The Ancient Greeks
By far the most famous early astronomers are the ancient Greeks. Between about 500BC and 100BC, they built a picture of the Universe which dominated for over 1000 years.
Thales (624 - 545 BC)
Realised that celestial objects were at different distances, that the Earth was spherical, and that the light of the moon was reflected sunlight.Pythagoras (582 - 500 BC)
Produced the first geocentric model of the Universe, with everything making perfectly circular orbits around the Earth.
Geocentric Model