Transcript here

ASTRO 101
Principles of Astronomy
Instructor: Jerome A. Orosz
(rhymes with
“boris”)
Contact:
• Telephone: 594-7118
• E-mail: [email protected]
• WWW:
http://mintaka.sdsu.edu/faculty/orosz/web/
• Office: Physics 241, hours T TH 3:30-5:00
Text:
“Discovering the Essential Universe,
Fifth Edition”
by
Neil F. Comins
Course WWW Page
http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012.html
Note the underline: … ast101_fall2012.html …
Also check out Nick Strobel’s Astronomy Notes:
http://www.astronomynotes.com/
No appointment needed!
Just drop by!
Where: Room 215, physics-astronomy building.
When:
• Monday:
• Tuesday:
• Wednesday:
• Thursday:
12-2, 4-6 PM
12-1 PM; 4-6 PM
12-2, 5-6 PM
4-6 PM
Homework
• Homework due September 18: Question 11
from Chapter 2 (In what ways did the
astronomical observations of Galileo support a
heliocentric cosmology?)
• Write down the answer on a sheet of paper and
hand it in before the end of class on September
18.
Homework
• Go to a planetarium show in PA 209:
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Wednesday, September 12:
12:00 PM -- 12:30 PM
Thursday, September 13:
12:00 PM – 12:30 PM
12:30 PM – 1:00 PM
Friday, September 14:
12:00 PM – 12:30 PM
12:30 PM – 1:00 PM
Monday, September 17:
12:00 PM – 12:30 PM
12:30 PM – 1:00 PM
Thursday, September 20:
12:00 PM – 12:30 PM
12:30 PM – 1:00 PM
AND
4:00 PM – 4:30 PM
Friday, September 21:
12:00 PM – 12:30 PM
12:30 PM – 1:00 PM
AND
AND
AND
AND
AND
• Get 10 points extra credit for homework part of grade.
• Sign up for a session outside PA 209.
• Hand in a sheet of paper with your name and the data and time of
the session.
Next:
Lunar and Solar Eclipses
Lunar and Solar Eclipses
• But first, let’s discuss “angular size” and
“linear size”…
Angular Size
• The physical size is
measured in meters,
light-years, etc.
• The distance is
measured in the same
units.
• The angular size is
how large something
“looks” on the sky,
and is measured in
degrees.
Angular Size
• The angular size is
how large something
“looks” on the sky,
and is measured in
degrees.
• As you move the
same object further,
its angular size gets
smaller.
Angular Size
• The angular size is
how large something
“looks” on the sky,
and is measured in
degrees.
• If two objects are at
the same distance, the
larger one has the
larger angular size.
Angular Size
• Trick photography often involves playing with
different distances to create the illusion of large
or small objects:
http://www.tadbit.com/2008/03/06/top-10-holding-the-sun-pictures/
http://www.stinkyjournalism.org/latest-journalism-news-updates-45.php
Angular Size
• This figure illustrates how objects of very different
sizes can appear to have the same angular sizes. The
Sun is 400 times larger than the Moon, and 390 times
more distant.
Lunar and Solar Eclipses
• A solar eclipse is seen when the Moon
passes in front of the Sun, as seen from a
particular spot on the Earth.
• A lunar eclipse is seen then the Moon
passes into the Earth’s shadow.
Shadows
• If the light source is extended, then the shadow of an
object has two parts: the umbra is the “complete”
shadow, and the penumbra is the “partial shadow”.
Shadows
• If the light source is
extended, then the
shadow of an object has
two parts: the umbra is
the “complete” shadow,
and the penumbra is the
“partial shadow”.
Lunar Eclipses
• During a total lunar eclipse, the Moon passes through
Earth’s shadow.
Solar Eclipses
• The umbral shadow of
the Moon sweeps over
a narrow strip on the
Earth, and only people
in that shadow can see
the total solar eclipse.
Solar Eclipses
• The umbral shadow of
the Moon sweeps over
a narrow strip on the
Earth, and only people
in that shadow can see
the total solar eclipse.
Solar Eclipses
• The umbral shadow of
the Moon sweeps over
a narrow strip on the
Earth, and only people
in that shadow can see
the total solar eclipse.
• During totality the
faint outer atmosphere
of the Sun can be seen.
Annular Eclipses
• The angular sizes of
the Sun and Moon
vary slightly, so
sometimes the Moon
isn’t “big enough” to
cover the Sun
Lunar and Solar Eclipses
• Why isn’t there an eclipse every month? Because the orbit of the
Moon is inclined with respect to the orbital plane of the Earth
around the Sun.
How often do we see an Eclipse?
• Roughly every 18 months there is a total solar
eclipse visible somewhere on the Earth.
Next:
The Scientific Method
Gravity and the motions
of the planets
Outline of the Scientific Method
• Gather data, make observations, etc.
• Form a hypothesis on how the object of
interest works.
• Determine the observable consequences of
your idea, using reasonable assumptions
and well-established “laws.”
• Formulate experiments to see if the
predicted consequences happen.
Outline of Scientific Method
• If the new observations agree with the
predictions: great, keep going.
• If the new observations don’t agree with
the predictions: start over!
Outline of Scientific Method
A Good Recap From Nick Strobel
http://www.astronomynotes.com/scimethd/s1.htm
Next:
The motion of the planets
A Brief History of Astronomy
Stonehenge (c. 2000 B.C.)
Stonehenge was probably used to observe the sun and
Moon. Image from FreeFoto.com
The great pyramids of Egypt were aligned north-south.
A Brief History of Astronomy
• An early view of the skies:
 The Sun: it rises and sets, rises and sets…
 The Moon: it has a monthly cycle of phases.
 The “fixed stars”: the patterns stay fixed, and
the appearance of different constellations marks
the different seasons.
• Keep in mind there were no telescopes, no
cameras, no computers, etc.
A Brief History of Astronomy
• But then there were the 5 “planets”:
 These are star-like objects that move through the
constellations.
 Mercury: the “fastest” planet, always near the Sun.
 Venus: the brightest planet, always near the Sun.
 Mars: the red planet, “slower” than Venus.
 Jupiter: the second brightest planet, “slower” than
Mars.
 Saturn: the “slowest” planet.
A Brief History of Astronomy
• By the time of the ancient Greeks (around
500 B.C.), extensive observations of the
planetary positions existed. Note, however,
the accuracy of these data were limited.
• An important philosophical issue of the
time was how to explain the motion of the
Sun, Moon, and planets.