Download Our Place in the Cosmos and Introduction to

Our Place in the
Cosmos
and
Introduction to
Astrophysics
Jon Loveday
Astronomy 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%)
Lecturer
 Jon Loveday
 Pev2 5A5 x 7719
 J.Loveday@sussex.ac.uk
 Office hour: Tuesday 1.30-2.30
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 pseudoscience
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
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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
Solar System
Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Milky Way
Milky Way as Viewed from Earth
NGC 891
Milky Way in the near-IR
NGC 4414
Virgo Galaxy Cluster
A cluster of galaxies
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
Distances as light travel times - not to scale!
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
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
Earliest depictions of the skies are found in the Cave
paintings in Lascaux, SW France (c15,000 BC)
Dots below horses thought to represent changing phases
of the Moon
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
El Castillo, Chichen Itza
(Mayan, c1000 AD)
At sunset close to the spring and autumn equinoxes, shadows give
the effect of a snake slithering down the stairway.
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