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

• 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

http://www.spaceweather.com/

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

• 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 – Full Moon– Visible to many– Longer duration– Moon darkened– Not dangerous– Types

• Total (all umbral)• Partial (part umbral)• Penumbral (lame!)

• Solar– New Moon– Visible to few– Shorter duration– Sun blocked– Dangerous– Types

• 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 TriangleKeystone

TeapotFish hook

Northern Cross

4 C’s

M/W

Great Square of Pegasus

Beehive

Kids

7 SistersPleiadesSubaru

Belt of OrionSword of OrionWinter Triangle

Heavenly “G”

Kite, Ice cream Sickle

Little DipperBig Dipper

Measuring Stars

• Magnitude Scale1 – brightest2 – not so bright3 – even fainter4 – fainter stillEtc.

• Apparent Magnitude Scale (m)

ExamplesStar m Sun -26.4Sirius -1.4Vega 0Polaris 2.0Arcturus-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

South Celestial Pole

CelestialEquator

Dec = 0º

Northern Dec

Southern DecRA

North Celestial Pole

South Celestial Pole

CelestialEquator

Ecliptic

IT IS ONLY A MODEL!NOT REALITY!

• 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…