Sun - Major Misconceptions
The Sun orbits around the Earth during the
course of the day.
Seasons are caused by the Earth’s changing
distance to the Sun.
The Sun will be directly over your head at noon
during the summer.
The Sun will always rise/set due east/west as
seen from Iowa.
The Sun
• “Motion” vs Reality
– Sun’s daily “motion” → OUR MOTION
• We see the Sun appear to rise, set
– Sun’s yearly “motion” → OUR MOTION
• We see the Sun’s position relative to the stars change
• We see the Sun’s position relative to the horizon change
• Important factors
– The Earth is tilted relative to its orbit
– Your location & date determines where/when you
see the Sun
Located over the Earth’s equator – Equinox (Vernal and Autumnal)
At the most northerly point – Summer Solstice
Above the “Tropic of Cancer”, Latitude = 23.5º N.
At the most southerly point – Winter Solstice
Above the “Tropic of Capricorn”, Latitude = 23.5º S.
WHAT???
On December 21 the Sun is located above the Tropic of Capricorn?
Why not the “Tropic of Sagittarius”?
Astrology!
• Pseudoscience
– 12 signs of the zodiac
– People who waste a lot of time/money
– People who earn a lot of money!
• Originates with ancient Babylonians,
Egyptians
– Around 2000 BCE
– Since then things have changed…
Let’s check out some animations….
Precession
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Alters our alignment to the sky/stars
Alters our alignment to the Sun
Alters calendars (until around 1600)
Demonstrate “wrong sign”
Sky View Café
Observing the Sun
• SAFETY
• Avoid magnification if possible
– Projection is best
• Avoid overheating equipment
– Open ended telescopes (simple reflectors)
– Light blocking filters
• Use only REAL SOLAR FILTERS
– Block 99.999% of sunlight
What’s to see?
• Sun spots (well, maybe)
– Check before hand
• Solar Cycle
• Solar Activity
– Aurora
– Flares
Lunar Misconceptions
• The Moon does not rotate because we see only
one side of it.
• The dark side of the Moon always faces away
from the Earth.
• The Moon causes seasons.
• The Moon is only visible at night.
• Phases are caused by the Earth’s shadow.
Phases
• Entire cycle takes 29.53 days
• Approximately 1 week between major phases
– New, First Qtr, Full, Third/Last Qtr
• Time scale
– Earth rotates faster (~24 hours versus ~30 days)
– Moon slowly moves relative to the stars
– Daily change in position notable
Is this good?
Physical Model
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3-D
Interactive
Pace of motion (Earth and Moon)
Alignments
– Earth-Sun = Time of day
– Earth-Moon-Sun = Phase of Moon
• Light variation
Eclipses
• Lunar
• Solar
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Full Moon
Visible to many
Longer duration
Moon darkened
Not dangerous
Types
• Total (all umbral)
• Partial (part umbral)
• Penumbral (lame!)
New Moon
Visible to few
Shorter duration
Sun blocked
Dangerous
Types
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Total
Annular
Partial
Hybrid
Movie
St Louis Movie
Stars
• Constellations
– 88 Regions in the sky
– NOT JUST THE STICK FIGURES!
– Cultural origins
• Asterisms
– Useful tool
– Informal – not official!
Summer Triangle
Keystone
Northern Cross
Fish hook
Teapot
4 C’s
M/W
Great Square of Pegasus
Kids
Beehive
Winter Triangle
Heavenly “G”
7 Sisters
Pleiades
Subaru
Belt of Orion
Sword of Orion
Little Dipper
Big Dipper
Kite, Ice cream
Sickle
Measuring Stars
• Magnitude Scale
1 – brightest
2 – not so bright
3 – even fainter
4 – fainter still
Etc.
• Apparent Magnitude
Scale (m)
Examples
Star
Sun
Sirius
Vega
Polaris
Arcturus
m
-26.4
-1.4
0
2.0
-0.1
Celestial Sphere
• A Model – NOT REALITY
• Tool for mapping
• Define Coordinate system
– Right Ascension, Declination
– Celestial Equator, Celestial Pole
– NO DEPTH/DISTANCE
North Celestial Pole
Northern Dec
Celestial
Equator
Dec = 0º
RA
Southern Dec
South Celestial Pole
North Celestial Pole
Ecliptic
Celestial
Equator
South Celestial Pole
IT IS ONLY A MODEL!
NOT REALITY!
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Sun doesn’t orbit the Earth – Earth orbits!
Orbits are not circles!
Stars are not on a giant sphere!
Distances are much greater!
Motions (real and apparent) = units of time
– Apparent motion of stars = 23:56 = Sidereal day
– Apparent motion of Sun = 24 hours = Solar day
– Rotation of the Earth = ?
Sidereal Day (23:56)
Apparent motion of the stars
• Generally “east” to “west”
• Except for circumpolar stars
• Time for some more animation…