Survey of Astronomy

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Survey of Astronomy

• Mr. Lee is Instructor

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Survey of Astronomy

• Mr. Lee is the Instructor
• Please take one each of the papers up front

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My e-mail

• By far the best way to contact me is by e-mail
• tom.lee_at_nuvontmail.com

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My Web Page

• http//www.astro1010-lee.com/
• Syllabus
• Copies of my Slides
• Copies of my Lecture Notes
• Links

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Syllabus

• Text no text study the slides on line
• Tests
• 5 unit tests
• NO comprehensive final
• Must be taken on the day scheduled (I can change
  the date but you can NOT)
• Absolutely no late tests
• May be taken early
• I DROP YOUR LOWEST TEST SCORE

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Other Info

• Astrolabs
• You need to attend one
• Dr. Powell offers only a finite number
• I recommend that you go to an early one

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Exercise 1
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Eratosthenes Method
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Exercise 1

• Variation on Eratosthenes method
• Requires
• Protractor
• Thread
• Tape
• Weight
• Find the North Star

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Protractor
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How to find Polaris
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How to Measure it
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North Celestial Pole

• The NCP is a direction not a place

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Angle to NCP from different Latitudes
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Exercise 1
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Angular Measure
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Angular/Linear Measurement
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Angular Units

• Degree (of arc) 1/360 Circle
• Minute (of arc) 1/60 of a Degree
• Second (of arc) 1/60 of a Minute
• Hour (of arc) 360/24 15 degrees

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• The Terrestrial Coordinate System

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Picture Yourself on the Earths Surface
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Zenith, Horizon Horizon
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Altitude/Azimuth
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• Reference points and planes on the
• Celestial Sphere

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• Hour Angle (RA)
• Declination (d)

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Our Place in Space
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Our Place in Space
Earth is average we dont occupy any special
place in the universe Universe totality of all
space, time, matter, and energy
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Astronomy study of the universe Scales are very
large measure in light-years, the distance light
travels in a year about 10 trillion miles
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Astronomical Numbers
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This galaxy is about 100,000 light-years across
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Scientific Theory and the Scientific Method
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Scientific Theory and the Scientific Method

• Scientific theories
• must be testable
• must be continually tested
• should be simple
• should be elegant
• Scientific theories can be proven wrong, but they
  can never be proven right with 100 certainty

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Scientific Theory and the Scientific Method
Observation leads to a theory explaining
it Theory leads to predictions consistent with
previous observations Predictions of new
phenomena are observed. If the observations agree
with the prediction, more predictions can be
made. If not, a new theory can be made.
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The Obvious View
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The Obvious View
Simplest observation look at the night sky About
3000 stars visible at any one time distributed
randomly but human brain tends to find patterns
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The Obvious View
Group stars into constellations figures having
meaning to those doing the grouping Useful
Polaris, which is almost due north
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The Obvious View
The Moving Sky Polaris does not move
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The Obvious View
Stars that appear close in the sky may not
actually be close in space
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The Obvious View
The celestial sphere Stars seem to be on the
inner surface of a sphere surrounding the Earth
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Celestial Coordinates
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Celestial Coordinates

• Declination degrees north or south of celestial
  equator
• Right Ascension measured in hours, minutes, and
  seconds eastward from position of Sun at vernal
  equinox

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Earths Orbital Motion
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Earths Orbital Motion

• Daily cycle, noon to noon, is Diurnal motion
  Solar day

Stars arent in quite the same place 24 hours
later, though, due to Earths revolution around
Sun when they are, one Sidereal day has passed
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Earths Orbital Motion
Seasonal changes to the night sky are due to
Earths motion around Sun
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Earths Orbital Motion
12 constellations that the Sun moves through
during the year are the zodiac the path is the
ecliptic
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Earths Orbital Motion
Ecliptic is plane of Earths path around Sun at
23.5 to celestial equator Northernmost point
(above celestial equator) is summer solstice
southernmost is winter solstice points where
path crosses celestial equator are vernal and
autumnal equinoxes

• Time from one vernal equinox to next is tropical
  year
• Combination of day length and sunlight angle
  gives seasons

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Earths Orbital Motion
Precession rotation of Earths axis itself
makes one complete circle in about 26,000 years
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Earths Orbital Motion
Time for Earth to orbit once around Sun, relative
to fixed stars, is sidereal year Tropical year
follows seasons sidereal year follows
constellations in 13,000 years July and August
will still be summer, but Orion will be a summer
constellation
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Astronomical Timekeeping
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Astronomical Timekeeping
Solar noon when Sun is at its highest point for
the day (on the meridian) Drawbacks length of
solar day varies during year noon is different
at different locations
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Astronomical Timekeeping
Solar noon when Sun is at its highest point for
the day Drawbacks length of solar day varies
during year noon is different at different
locations
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Astronomical Timekeeping
World time zones
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Astronomical Timekeeping
Lunar month (complete lunar cycle) doesnt have
whole number of solar days in it, and tropical
year doesnt have whole number of months Current
calendar has months that are close to lunar
cycle, but adjusted so there are 12 of them in a
year
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Astronomical Timekeeping

• Year doesnt quite have a whole number of solar
  days in it leap years take care of this.
• Add extra day every 4 years
• omit years that are multiples of 100 but not of
  400
• omit years that are multiples of 1000 but not of
  4000.
• This will work for 20,000 years.

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Astronomical Timekeeping
Moon takes about 29.5 days to go through whole
cycle of phases synodic month Phases are due to
different amounts of sunlit portion being visible
from Earth Time to make full 360 around Earth,
sidereal month, is about 2 days shorter
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Motion of the Moon
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Motion of the Moon
Eclipses occur when Earth, Moon, and Sun form a
straight line
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Motion of the Moon

• Lunar eclipse
• Earth is between Moon and Sun
• partial when only part of Moon is in shadow
• total when it all is

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Motion of the Moon
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Motion of the Moon
Eclipses dont occur every month because Earths
and Moons orbits are not in the same plane
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The Measurement of Distance
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The Measurement of Distance
Triangulation measure the baseline and angles,
can calculate the distance
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The Measurement of Distance
Parallax similar to triangulation, but looks at
apparent location of object against distant
background from two vantage points
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Study Hints

• Review the Slides
• Study the Lecture Notes
• Note especially what I emphasize in class

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In Class Quiz

• Where do you come from?
• What is your year in school?

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GO TO CHAPTER 2