Download Integrative Studies 410 Our Place in the Universe

What time is it?
• Depends on where you are on the Earth!
• Time zones ensure that the noon is really
noon, i.e. sun is at highest point
• To avoid confusion, use universal time (UT),
the time at the meridian in Greenwich
UT = EST + 5 hrs
• Daylight savings adds one hour in spring, so
UT = EDT+ 4 hrs
The Time Zones
Established to insure that sun is at highest point
approximately at noon in the middle of the time zone
Daily and yearly motion intertwined
Solar vs Siderial Day
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Earth rotates in 23h56m
also rotates around sun
 needs 4 min. to “catch
up”
Consequence: stars rise 4
minutes earlier each
night (or two hours
per month, or 12
hours in ½ year)
After 1/2 year we see a completely different sky at night!
Carl Sagan Article: Baloney
Detection Kit
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Occam's Razor
Authorities do NOT carry a lot of weight
Ask whether the hypothesis can be falsified
Use MANY hypotheses to explain
experimental facts
• There must be an independent confirmation
of the facts
• Quantify!
Bacon: The subtlety of Nature is
greater than the subtlety of
argument.
• Often Nature is much weirder than we think
(or are used to from our every day
experiences)
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At very large speeds (Relativity)
For very small objects (Quantum Mechanics)
For very dense objects (Black Holes)
Etc.
Fallacies of logic and rhetoric
• Ad hominem
• Non sequitur
• Appeal to ignorance
• Begging the question
• Observational selection
 You may influence public opinion, but for
scientific progress, all that matters is
agreement with observations
Seasonal Motion
• Daily Rising and Setting:
– Due to the rotation of the
Earth around its axis
– Period of rotation:
1
siderial day= 23h56m4.1s
– 1 solar day (Noon to Noon) =24h
– Stars rotate around the
North Star – Polaris
• Seasonal Changes:
– Monthly differences caused
by Earth’s orbit around sun
The Zodiac throughout the Year
Example: In Winter sun in Sagittarius, Gemini at night sky;
in summer sun in Gemini, Sagittarius at night sky
Another Complication: Axis Tilt!
• The Earth’s rotation axis is tilted 23½ degrees
with respect to the plane of its orbit around
the sun (the ecliptic)
• It is fixed in space  sometimes we look
“down” onto the ecliptic, sometimes “up” to it
Rotation axis
Path around sun
Activity: The Ecliptic
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Get out your activities book
Form a group of 3-4 people
Work on the questions
Hand in a sheet of paper with the title of the
activity and the names of the group
members
• I’ll come around to help out !
The Seasons
• Change of seasons
is a result of the tilt
of the Earth’s
rotation axis with
respect to the plane
of the ecliptic
• Sun, moon, planets
run along the
ecliptic
Animation
• TeacherTube video
Position of Ecliptic on the Celestial Sphere
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Earth axis is tilted w.r.t. ecliptic by 23 ½ degrees
Equivalent: ecliptic is tilted by 23 ½ degrees w.r.t. equator!
 Sun appears to be sometime above (e.g. summer
solstice), sometimes below, and sometimes on the celestial
equator
Zodiacal signs vs. Constellations
•“Constellation” is a modern,
well-defined term
- Some constellations are big, some
are small on the celestial sphere
•“Zodiacal sign” is the old
way of dividing the year and
the Sun’s path into 12 equal
parts
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360/12=30, so each zodiacal sign is exactly 30 degrees “long”
0 degrees: Aries, 30 degrees: Taurus, 60 degrees: Gemini, 90
degrees: Cancer, etc.
Example
The vernal equinox
happens when the
sun enters the
zodiacal sign of
Aries, but is actually
located in the
constellation of
Pisces.