Introduction to Astronomy

1
Introduction to Astronomy

• Physics 103

Dr. Julie A Rathbun Dr. Tyler E Nordgren
2
Topics The Night Sky
3
from the Solar System
4
to the Stars
5
to the Milky Way
6
and to the Universe Beyond.
7
Our Goal

• Understand
• The sky above
• Whats that bright red star to the south?
• News reports
• Scientists discover giant black hole.
• Popular entertainment
• Armageddon, Mission to Mars, etc
• Learn how science works and how we know what we
  know.

8
Organization

• Lecture one night a week for 3 hours
• 2 lectures plus outdoor viewing
• Lab one night a week (Wed. or Thurs.)
• Meet in lab room about EVERY OTHER WEEK.
• Check the Syllabus for exact dates!

9
How the Class Works

• Combine 3 hour Lecture with outdoor viewing.
• Homework assigned in Lecture.
• Formal Labs about every other week.
• Weeks without Lab we will assign small Observing
  projects.
• Record ALL observations in an Observing Notebook.
• 2 one-hour in-class exams.
• One final.

10
Grading

• Labs 18
• Observing notebook 18
• Homework assignments 18
• 2 In-class exams 24
• Final 22

11
The Sky What do YOU see?

• A sphere of stars.
• Are they spaced uniformly?
• Do they move?
• Do they move relative to each other?
• Some do How do they move?
• What are those two bright things (one of which is
  always up during the day)?
• How do they move and change?

12
The Projected Sky

• Stars are at different distances.

• But we see them projected on to a plane.

13
A Sphere of Stars

• We see the entire Universe projected on to a
  sphere.
• The stars are scattered randomly on this sphere
  (except for the Milky Way).
• In this randomness, we see pictures
  Constellations.

14
Constellations
15
As the World Turns

• As the Earth turns on its axis, the stars (and
  everything else) move from east to west.
• Only the North Star (Polaris) appears to stand
  still.
• There is no Southern Star.

16
The Fixed Stars

• The stars are fixed relative to one another.
• The constellations you see today are the ones
  that ancient peoples saw long ago.
• Over thousands to millions of years even these
  constellations will change as stars move through
  the galaxy.
• On time scales of weeks to years, however, five
  stars are seen to move relative to the
  others.
• The Wanderers the 5 naked-eye Planets.

17
Venus
18
The Sun and Zodiac

• As the Earth orbits the Sun, the Sun appears to
  move through some constellations.
• These constellations are the Zodiac.
• The path the Sun follows is called the Ecliptic.

• The Suns light always blots out the stars behind
  it.
• Result Seasonal constellations.

19
Seasons

• The North Pole of the Earth is not perpendicular
  to the plane in which it moves around the Sun.
• The result is Seasons.
• Northern Summer When the Northern hemisphere is
  tilted towards the Sun (Southern winter).
• Northern Winter When the Northern hemisphere is
  pointed away from the Sun (Southern Summer).

20
Solstices, Equinoxes, Oh My.

• Summer Solstice June 21 The longest day of the
  year. The Sun reaches its highest point in the
  sky.
• Winter Solstice December 21 The shortest day
  of the year. The Sun is at its lowest.
• Spring Equinox March 21 The days and nights
  are EQUAL.
• Fall Equinox September 21 Its the same then
  too.

21
The Moon and Phases

• The Moon takes 27.3 days to orbit the Earth.
• The Moon takes 27.3 days to turn on its axis.
• Result We always see the same face.
• There is no dark side of the Moon.

22
Lunar Eclipse

• Sometimes the Moon passes through the Earths
  shadow as cast by the Sun.

23
Composite photo of the January 2001 lunar eclipse.
24
Solar Eclipse

• Sometimes the Moon passes between the Sun and the
  Earth (and casts a shadow on the Earth).

August 1999 eclipse. Photo from crew of Mir.
25
Composite photo of August 1999 solar eclipse.
26
Types of Solar Eclipses

• Partial
• Total
• Annular

27
Angular Size

• The Sun is a million times larger than the Earth.
• The Moon is a fourth the size of the Earth.
• The distance from the Earth determines their
  ANGULAR SIZE.
• Angular size How big does something look as
  viewed from the Earth.

28
Angles

• The sky is 360 arc degrees around.
• 60 arcminutes 1 arc degree
• The Full Moon is about half an arc degree
  30 arcminutes.
• 60 arcseconds 1 arcminute
• Mars is about 2 arcminutes now.
• 1000 milliarcsecond 1 arcsecond
• Polaris is 46 milliarcseconds in diameter
• An astronaut on the Moon is 2 milliarcseconds
  tall!

29
Angular vs. Linear (True) Size

• How big an object LOOKS from the Earth depends
  upon its TRUE size (Linear Size) and distance
  from Earth
• Angle Linear Size / Distance

30
(No Transcript)