Chapters 1, 2: Introduction, Earth and Sky Orientation to the Universe - sizes and distances Frames of Reference: equator, ecliptic, horizon
The Seasons Eclipses of the sun and moon Key Points The most abundant element in Universe: Hydrogen Know how the sky turns if you are on the Earths equator,
mid-latitudes, and poles. Know the seasons and where the sun is during each of them. Earths orbit is elliptical, closest to sun Jan 4, farthest on July 4, but only different by 2% Know why summers warmer than winters
Lunar eclipses: moon passes into Earths shadow, always at Full moon phase Solar eclipse: moons shadow cast onto Earth, always at New Moon phase. Just know the basic names of the phases of the moon, for reference when we get to tides and eclipses
Dimensions, Units Distance often given terms of light travel time @ speed of light = 300,000 km/sec Moon is 2 light seconds away Sun is 8 light minutes away
Astronomical Unit = 1 AU = ~avg distance Earth-to-sun Solar system is ~1 light day across Nearest star is 4 light years away Milky Way Galaxy is ~100,000 light years across Andromeda Galaxy nearest galaxy like our own
is 2 million light years away The observable universe is 13.7 BILLION light years radius 1 light year = about 63,241 AU And What is Most of what we
see made of? Hydrogen! = 1 proton and one electron zipping around it. The simplest atom 90% of all atoms in the universe are hydrogen atoms
Dont be fooled You, me, this room all are very Untypical in their chemical composition. The 4 Forces Governing the Universe
All (almost all?) natural processes can be described by just 4 fundamental forces of nature in order from strongest to weakest: Two Short Range (Nuclear) forces: 1. The Strong Force (acts between baryons: [protons, neutrons, pions])
2. The Weak Force acts between certain other elementary particles And Two Long Range Forces: 3. Electromagnetism (acts between charges) 4. Gravity (acts between masses)
Back to Earth lets get started How does the sky behave, and why? What causes the seasons? The earth and its motions and how this affects the sky
Did all the Ancients figure the Earth was Flat? You might think so, but the ancient Greeks figured out it was a sphere. How? By watching eclipses of the moon
and noting they always happened 180 degrees away from the sun, and cut a circular shadow regardless of time of day. Only one figure cuts a circular shadow no matter how its turned - a sphere
They even measured how big it was, correctly! Way back in ~250BC. StarTrailsKilamanjaro The Seasons
Primary cause Earths rotation axis is tilted relative to orbital axis Why warmer in summer.(1) more daylight hours, and (2) daytime sun is higher in the sky Earths orbit is nearly a circle: 92 million miles at closest, 94 million at farthest conclusion:
not much, and so doesnt affect annual temperatures much At Santa Cruz latitude, distance only makes 4% difference in heating, while seasonal effect is a factor of 2; i.e. much larger.
Axis vs orbit tilt Solstices and Equinoxes Equinox Equal periods of Night. Everywhere gets 12 hours of daylight, 12 hours of night. Solstice - sun stands still. The sun has reached
farthest north or south of the celestial equator, and reverses direction. Winter Solstice: Dec 21. Sun is farthest south, 23 degrees south of the celestial equator Spring Equinox: Mar 21. Sun crosses the celestial equator heading north
Summer Solstice: June 21. Sun is farthest north, 23 deg north of the celestial equator Fall Equinox: Sept 21. Sun crosses the equator heading south. Seasons diagram
Precession Axis Tilt, not Distance to Sun, Causes Seasonal Temperature Differences
Common misconception sun is farther in winter, closer in summer. Nope! Earths orbit IS elliptical and distance to the sun does vary, but not by much; 91.9 million miles vs 94 million miles. How much would you expect this would affect
temperatures? (follow Rick on the white board) Interesting Facts: Were closest to the sun on January 4th Were farthest from the sun on July 4th
(plus or minus a day or two because of leap year) Eclipses of the Sun and Moon Eclipses happen when earths shadow
follows on the moon (Lunar Eclipse), or moons shadow falls on the earth (Solar Eclipse). How would this affect when/if eclipses happen?
Solar eclipse types SanDiegoAnnular Ponder what are the circumstances which would make for the largest
annular ring of sunlight during an annular eclipse. How far should be the sun? the moon? What day would you want? What time of day?
Solar eclipse sequence Solar Totality from Space Antarctic Eclipse, grazing shadow geometry
Time Lapse Total Lunar Eclipse Total lunar eclipse from the moon
lunarEclUmbraPenumbra Lunar eclipse types Penumbral eclipse sequence
CompleteLunarEcl Varying shadow colors as sunlight refracts through Earths atmosphere to hit the totally eclipsed moon
totalEclipseZubenalgenubi The Phases of the Moon Half the moon is always sunlit and half always dark, obviously. But the amount of the sunlit side we see
varies as the moon orbits the Earth Full moon when its opposite the sun and so its fully sunlit. New moon when its in the same direction as the sun so the dark side faces us
How do the Moons phases look, from high above the Earth/Moon system, compared to here on the ground? This link tells all! Very nice.
http://aa.usno.navy.mil/graphics/Mo on_movie.gif The Phases of the Moon These 3 quantities are related. Given any
two, you can ponder and see what the third must be 1. The phase of the moon 2. The time of day 3. The place of the moon in the sky This used to be one of my favorite quiz
questions! This Photo is a Tease! Well Discuss in Chapter 4 Chap 2 Earth and Sky; Key Points
The most abundant element in Universe: Hydrogen Know how the sky turns if you are on the Earths equator, mid-latitudes, and poles. Know the seasons and where the sun is during each of them. Earths orbit is elliptical, closest to sun Jan 4, farthest on
July 4, but only different by 2% Know why summers warmer than winters Lunar eclipses: moon passes into Earths shadow, always at Full moon phase Solar eclipse: moons shadow cast onto Earth, always at New Moon phase.
Just know the basic names of the phases of the moon, for reference when we get to tides and eclipses
