Before you Sit
Please Pick-up:
Blue Information Sheet for Evening Observing.
1 Red and 1 Blue ticket for Observing/Planetarium
Tuesday, August 31, 2010
Evening Observing
Observing at the Brooks Observatory: Three different weeks (M-Thu) for this semester:
Sep 20-23 (starting at 9pm)
Oct 18-21 (>8:30pm)
Nov 15-18 (>7:30pm)
Suggestion: Go Earlier in the semester: Warmer, less crowding (better chance to look), better weather (less chance of a waster trip).
Tuesday, August 31, 2010
Announcements/Assignments
Need syllabus/schedule/ABCD card? See me after class.
Finish reading Chapter 2 by Thu.
First graded online homework: “Homework #1” due Friday, Sept. 3rd 11:45pm. Available now.
Reminder: Lecture notes are posted on the course website after class.
Tuesday, August 31, 2010
M.A. Homework Notes
Late Homework: 10% off per day.
Grading: 2% bonus per hint not used (use them!).
“sorting”-type questions: Only 3% off for wrong answers.
Still need help with MasteringAstronomy.com? See me after class.
Tuesday, August 31, 2010
Which is the correct order of events, according to the current accepted scientific theory of the origin and evolution of the Universe?
A) Birth of Universe, solar system forms, first stars and galaxies, first life on Earth
B) First stars and galaxies, birth of Universe, solar system forms, first life on Earth
C) Solar system forms, birth of Universe, first stars and galaxies, first life on Earth
D) Birth of Universe, first stars and galaxies, solar system forms, first life on Earth
A BC D
Review
Tuesday, August 31, 2010
Which is the correct order of events, according to the current accepted scientific theory of the origin and evolution of the Universe?
A) Birth of Universe, solar system forms, first stars and galaxies, first life on Earth
B) First stars and galaxies, birth of Universe, solar system forms, first life on Earth
C) Solar system forms, birth of Universe, first stars and galaxies, first life on Earth
D) Birth of Universe, first stars and galaxies, solar system forms, first life on Earth
✪
A BC D
Review
Tuesday, August 31, 2010
Last Time
Earth’s Rotation (once per day) causes sun/stars/etc. to rise in the east, transit at their highest point at the meridian, and then set in the west. Zenith is the point directly overhead.
The Stars you see depends on your latitude. Some stars are always up: they are circumpolar.
Constellations: Just random groupings of stars invented by humans.
The celestial sphere is an imaginary sphere where we place stars on a two dimensional grid, similar to latitude and longitude on earth.
Tuesday, August 31, 2010
Last Time
1 degree=60 arcminutes = 3600 arcseconds.
The “size” of objects in the sky is measured as an angle. Without knowing its distance, we can’t know its true size.
Tuesday, August 31, 2010
From Toledo, you observe a star rising due east. When this star reaches its highest position above the horizon, where will it be?
A) high in the northern skyB) high in the eastern skyC) high in the southern skyD) high in the western sky E) directly overhead
A BC D
Star Rise
Tuesday, August 31, 2010
From Toledo, you observe a star rising due east. When this star reaches its highest position above the horizon, where will it be?
A) high in the northern skyB) high in the eastern skyC) high in the southern skyD) high in the western sky E) directly overhead
A BC D
Star Rise
Tuesday, August 31, 2010
From Toledo, you observe a star rising due east. When this star reaches its highest position above the horizon, where will it be?
A) high in the northern skyB) high in the eastern skyC) high in the southern skyD) high in the western sky E) directly overhead
✪
A BC D
Star Rise
Tuesday, August 31, 2010
Equator Star Trails
Imagine sitting at the equator at night as the Earth turns. What would the stars look like?
All stars rise and set
Polaris is located on the horizon
Horizon
Tuesday, August 31, 2010
Latitude and Longitude
How did sailors know their location on the Earth before GPS?
Tuesday, August 31, 2010
Horizon
at the North Pole, lat=90°, altitude of polaris=90°
Polaris
How to find your latitude on Earth?
★
Tuesday, August 31, 2010
How to find your latitude on Earth?
Horizon
at the Equator, lat=0°, altitude of polaris=0°
Po
lar
is
★
Tuesday, August 31, 2010
Star Trails in between....
Mauna Kea, Hawai’i
20°
Altitude of North Star =
your latitude!
Tuesday, August 31, 2010
Imagine you are located in the Northern Hemisphere and see a star directly overhead (zenith). In what direction will you have to look to see this star set?
A) southwestB) westC) northwest D) This star will
never set.
A BC D
Tuesday, August 31, 2010
Imagine you are located in the Northern Hemisphere and see a star directly overhead (zenith). In what direction will you have to look to see this star set?
A) southwestB) westC) northwest D) This star will
never set.
✪✪
A BC D
Tuesday, August 31, 2010
Apparent Motion of the SunAnnual (yearly) motion
Earth orbits Sun once per year
Sun seen in front of different constellations throughout year
The sun “slips” day to day on the celestial sphere, moving from W to E relative to the background of stars.
Tuesday, August 31, 2010
What Time is It?
Possible times: sunset, sunrise, midnight, noon
6am: Sunrise
Tuesday, August 31, 2010
What Time is It?
Possible times: sunset, sunrise, midnight, noon
12pm: Noon
6am: Sunrise
Tuesday, August 31, 2010
What Time is It?
Possible times: sunset, sunrise, midnight, noon
6pm: Sunset
12pm: Noon
6am: Sunrise
Tuesday, August 31, 2010
What Time is It?
Possible times: sunset, sunrise, midnight, noon
6pm: Sunset
12pm: Noon
6am: Sunrise
12am: midnight
Tuesday, August 31, 2010
The Day1 day = time for object to return to same point on sky (e.g. transit to transit)
Solar day (sun)
Time from noon until next noon
Sidereal day (star)
Time for a star to return to same point.
Tuesday, August 31, 2010
http://www.pfm.howard.edu/astronomy/Chaisson/AT401/IMAGES/AACHCIR0.JPGTuesday, August 31, 2010
Annual Path of Sun
Ecliptic
path of sun around celestial sphere
shape: circle
Zodiac
Set of 12 constellations containing Ecliptic
Sun in each constellation for about one month
(solar) signs of the zodiac
Tuesday, August 31, 2010
Solstice: Sun “stops” (moving N or S)
Summer Solstice
Jun 21=1st day of summer
Sun appears farthest North (from celestial equator)
Longest day of year
Winter Solstice
Dec 21=1st day of winter
Sun appears farthest South (from celestial equator)
Shortest day of year
Locations on Ecliptic
Tuesday, August 31, 2010
Locations on Ecliptic
Equinox: equal night and day
Vernal Equinox
~March 21 = 1st day of spring
Sun on equator (crossing from S to N)
Autumnal Equinox
~Sept 21 = 1st day of fall (autumn)
Sun on equator (crossing from N to S)
Equinoxes are intersection points of Ecliptic and Celestial Equator
Tuesday, August 31, 2010
Cause of SeasonsChanging distance to Sun?
Orbit is ellipse; distance changesGood idea, BUT...
Orbit almost circularTrivial change in distance (3%!)
little change in heating
Closest to sun in January
So this predicts summer in January! (wrong)
Both N and S hemispheres at same distancePredicts seasons same in N and S hemispheres (wrong)
Tuesday, August 31, 2010
Cause of SeasonsChanging distance to Sun?
Orbit is ellipse; distance changesGood idea, BUT...
Orbit almost circularTrivial change in distance (3%!)
little change in heating
Closest to sun in January
So this predicts summer in January! (wrong)
Both N and S hemispheres at same distancePredicts seasons same in N and S hemispheres (wrong)✕
Tuesday, August 31, 2010
Climate and LatitudeSun’s rays
spread over large area = cooler
concentrate in small area = warmer
Warmest where sun directly overhead (at noon)
cooler
warmer
cooler
Tuesday, August 31, 2010
Why Then?
Due to 23.5° tilt of the earth’s axis?
Sun up for longer, and higher in the sky = More sunlight = warmer: Summer
Sun up above horizon shorter time, and lower in the sky = Colder: Winter.
Tuesday, August 31, 2010
Why Then?
Due to 23.5° tilt of the earth’s axis?
Sun up for longer, and higher in the sky = More sunlight = warmer: Summer
Sun up above horizon shorter time, and lower in the sky = Colder: Winter.
✓Tuesday, August 31, 2010
Seasons: Interactive Figure
See Fig. 2.13
Tuesday, August 31, 2010
One night, you see the star Sirius rise at exactly 7:36 PM. The following night it will rise
A) slightly earlier B) at the same time C) slightly later
A BC D
Tuesday, August 31, 2010
One night, you see the star Sirius rise at exactly 7:36 PM. The following night it will rise
A) slightly earlier B) at the same time C) slightly later
✪
A BC D
Tuesday, August 31, 2010
One night, you see the star Sirius rise at exactly 7:36 PM. The following night it will rise
A) slightly earlier B) at the same time C) slightly later
✪
A BC D
Tuesday, August 31, 2010
The Earth Moves like a Top: “Precession”
Tuesday, August 31, 2010
What sign are You?
“Signs” of the zodiac: designed to indicate which constellations the sun is in.
Precession of the Earth’s axis
Tuesday, August 31, 2010
What sign are You?
“Signs” of the zodiac: designed to indicate which constellations the sun is in.
Precession of the Earth’s axis
Tuesday, August 31, 2010
The MoonThe moon is about 1 quarter the size of the Earth
It orbits the Earth every 27.5 days
On average, it is 380,000 km away
Tuesday, August 31, 2010
Phases of the Moon
Each complete cycle of the moon takes 29.5 days, hence the word “month”
It is longer than the orbital period (27.5 days) because of the Earth’s orbital motion: Just like solar vs. sidereal day!
Tuesday, August 31, 2010
Phases of the Moon 29.5 days
New
Crescent
First Quarter
Gibbous
Full
Gibbous
Last Quarter
Crescent
}}
Waxing
Waning
Moon visible in the afternoon/evening. Get “fuller” and sets later each day.
Moon visible in the late night/morning. Get “lesser” and rises later each day.
Tuesday, August 31, 2010
What causes moon phases?
A) Moon passes into the shadow of the earth.
B) Relative orientation of Sun, Moon, and Earth determines the phase.
C) Moon is made of cheese, and the north wind eats it day by day.
A BC D
Tuesday, August 31, 2010
What causes moon phases?
A) Moon passes into the shadow of the earth.
B) Relative orientation of Sun, Moon, and Earth determines the phase.
C) Moon is made of cheese, and the north wind eats it day by day.
✪
A BC D
Tuesday, August 31, 2010
Take Away
Earth’s orbit about the sun once per year controls the position of the sun and the seasons.
The sun appears to move slowly on the celestial sphere.
When the sun, earth, and moon are aligned, eclipses can occur (more next week!).
Don’t Forget: HW #1 Due next Friday.
Tuesday, August 31, 2010