Transcript 05CyclesOfTheSky_RJx

Objectives
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Explain why the Earth undergoes seasons. Explain why it is hot in the summer.
Explain why the Sun appears high in the sky during the summer but low in winter?
Define equinox and solstice? Sketch the Sun, Earth, and Earth’s orbit. On the
sketch, draw Earth and label the location of Earth at the solstices and equinoxes.
Show the tilt of Earth’s axis.
What is meant by the plane of the solar system? Where is the Sun in this plane?
the Moon? the planets? the stars?
What is meant by “the Sun is in Leo”?
What is the zodiac? Why is it significant? How many constellations are in the
zodiac according to astronomy? Why is it called the zodiac? Explain why you only
see some of the constellations of the zodiac at a given time.
Explain why the Sun is not in the constellation horoscopes say it is in when you are
born.
What distinguishes science from non-science? Give an example.
Name the five North Circumpolar Constellations. Why are these important to us in
MN?
Explain why Polaris is the North Star? Explain why the stars appear to revolve
around the North Star?
What is meant by the Earth’s precession? Is Earth’s precession a long or a short
time?
Cycles of the Sky: Part 2
• Moon
– Moon Phases, Motions, Formation
– Lunar and Solar Eclipses
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Zodiac, Ecliptic
Precession
North Circumpolar Constellations
Seasons
Moon Phases
Orerry with light
Moon Phases
Moon Position at Sunset
Horizons textbook
Moon Phases Continued
Moon Position at Sunrise
Moon rises ~50 minutes later every day
Horizons
From Last Moon Lecture
Conclusion on Moon’s motion:
• Minute to minute the Sun, Moon, stars
appear to rise in east and set in west due
to Earth’s spin (rotation).
• Day to day, Moon moves west to east due
to Moon’s orbit (revolution) around Earth.
(Also generally true for other planets, due to their
planet’s orbit.)
Moon Motion in
One Day
(~minute to minute)
EAST
WEST
On Earth the Sun, Moon & stars (generally) rise in the east
and set in the west because of Earth’s rotation (spin).
Moon Motion Day to Day
Moon’s
Orbit
Earth East
West
Moon
Moon Revolves
~12 deg/day
Day to day from Earth, the Moon moves EAST because of
the Moon’s revolution (orbit) around Earth.
US on Earth drawing
Origin of Moon
• Early Earth and Mars size object collide
• Moon formed out of particles orbiting around the
new collided Earth
• Moon is made up of materials found in Earth’s
crust (outer layer)
• How the Moon was formed
https://www.youtube.com/watch?v=mQAdYWcA7ig (1:56)
• One mathematical model of Moon formation:
https://www.youtube.com/watch?v=Fwl_JBQtH9o (0:41)
• Evolution of the Moon (after it formed)
https://www.youtube.com/watch?v=UIKmSQqp8wY (2:41)
Image: http://www.seti.org/node/1458
Lunar Eclipses
• Earth’s shadow
consists of a zone of
full shadow, the
umbra, and a zone of
partial shadow, the
penumbra.
• If the Moon passes
through Earth’s full
shadow (umbra), we
see a lunar eclipse.
• If the entire surface
of the Moon enters
the umbra, the lunar
eclipse is total.
© Cengage Learning 2014
Orerry with light
Total Lunar Eclipse
• A total lunar eclipse can last up to 1 hour and 40
minutes.
• During a total eclipse, the Moon has a faint, red
glow, reflecting sunlight scattered in the Earth’s
atmosphere.
Lunar Eclipse
Dates
• 1 – 2 lunar eclipses
per year usually
• Next one:
– Partial
– 8/7/2017
Size of the Sun & Moon from Earth
• From Earth
the size of
the Moon
and Sun
are about
the same!
The angular diameter of the Moon (~0.5o) is
almost exactly the same as that of the Sun.
This is a pure coincidence. The Moon’s linear
diameter is much smaller than that of the Sun.
Solar Eclipses
Due to the equal angular diameters, the Moon can
cover the Sun completely when it passes in front of
the Sun, causing a total solar eclipse.
Orerry with light
Solar Eclipses
The Moon’s shadow sweeps
across the Earth, over points
from where we can see a
solar eclipse.
Total Solar Eclipse
During a total solar eclipse, the solar
chromosphere, corona, and
prominences can be seen.
Diamond
Ring Effect
Solar Eclipse Types
1. Total
2. Annular
3. Partial
4. Hybrid (both total and annular)
• Types are due to the changing (angular) size of the
Moon and Sun seen from Earth because the orbits are
Wikipedia.com
not perfect circles (they are ellipses).
Solar Eclipse Dates
• About 1 per year; max time is ~7 minutes.
• Next Total Solar Eclipse in North America:
– Monday, August 21, 2017 (2:40)
• 2017 Information and Path
– http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html
Very Important Warning:
Never observe the Sun directly with your bare
eyes, not even during a partial solar eclipse!
Use specially
designed solar
viewing shades,
solar filters, or a
projection
technique.
Constellations
• Imaginary memory aids to describe sky
• 88 total constellations named in Earth’s
celestial sphere (previously 48 from
Ptolemy about 350 BC)
• Other versions around the world –
Chinese, Arabic and Islamic
Celestial Sphere
Zodiac Constellations
and the Ecliptic
http://lifeng.lamost.org/courses/astrotoday/CHAISSON/AT301/HTML/AT30103.HTM
Annual Motion of the Sun
• 12 traditional Constellations of the Zodiac seen throughout the
year because of Earth’s revolution.
• The zodiacal constellations are located along the Sun’s path on
Earth (Ecliptic).
• The Ecliptic is also the plane of Earth’s path around the Sun.
Orerry with Sagittarius
Two Versions of Zodiac
Constellations
• 13 Sidereal
Constellations
of the Zodiac
(used by
astronomers)
and includes
Ophiuchus
• 12 Tropical
Constellations
of the Zodiac
• All 13 are in
the ecliptic
plane
One constellation missing from the traditional zodiac signs.
http://spaceplace.nasa.gov/starfinder2/en/
Precession of Earth
• The Earth’s North pole currently points to Polaris so
we call Polaris our North Star
• 3 000 BC: North star = Thuban
– origin astrology about 1000 to 2000 BC, so born in a
different sign
• 14 000 AD: North star = Vega
• *26,000 year cycle
Parke’s
precession
video
(watch if you
miss lecture)
Precession wheel demo
What Sign Are you?
• Astrology is not a science; it is a belief system – not
testable or repeatable (science hallmarks: natural,
testable & simple)
• Astronomy uses the same names of constellations
and uses all 13 constellations in the ecliptic
• You can look up your astrology sign based on the 13
sidereal constellations and accurate north star here:
http://www.livescience.com/4667-astrological-sign.html
• More about this from NASA here:
http://spaceplace.nasa.gov/starfinder2/en/
North Circumpolar Constellations
• Don’t rise or set; visible year-round in mid-latitudes
• 5 North Circumpolar Constellations: Ursa Major (Big
Dipper), Ursa Minor (Little Dipper), Cassiopeia, Draco,
Cepheus
Globe & Celestial Sphere
http://antwrp.gsfc.nasa.g
ov/apod/ap040911.html
Seasons on Earth
• Caused by Earth’s Tilt which is about 23 degrees
Northern summer =
Southern winter
Globe
Northern winter =
Southern summer
Seasons
• When the northern hemisphere is tilted toward
the sun, it also experiences longer daylight.
• Show longer daylight with globe
• The Earth’s tilt causes longer daylight in one
hemisphere
Northern Hemisphere
Seasons
Fall
Winter
Orerry
Summer
Spring
• Equinox: equal
night and day
• Equinox is when
the Sun is
crossing Earth’s
equator
• Solstice: daylight
is longer in each
hemisphere
www.faculty.edfac.usyd.edu.au
Explanation with a friend
• Explain why the Earth undergoes seasons.
Explain why it is hot in the summer. Explain
why the Sun appears high in the sky during
the summer but low in winter?
• Write your own explanation with the help of a
classmate. Write 2-4 sentences to explain.
Homework
• Make a flashcard for each objective. Have someone else ask
you the objectives and see if you can answer. Review all
flashcards.
• Read text. (chapters/sections labeled in calendar)
• Do practice quizzes on D2L Brightspace
• Observation projects
– Earth-Sun Scaling Model
• Due today, Jan. 24; Must email by midnight - no late assignments
– Sunset Part 1 (sunset at 5pm) view Sun about 4pm
• See details in Observing Projects on class calendar
• Due: FEB. 14; Part 2: Mar. 28 to Apr. 25
– Moon Phases
• Jan. 19 to Mar. 2; observe 4 phases of the moon and record
• Test 1 is in 2 weeks on Tuesday, Feb. 7
– To prepare: student objectives, D2L quizzes, and text
– About 60 multiple choice questions. Bring a pencil.