Before you Sit - University of Toledo

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).


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.


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.


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


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


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.


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.



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




A BC D

Star Rise




✪

A BC D

Star Rise


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


Latitude and Longitude

How did sailors know their location on the Earth before GPS?


Horizon

at the North Pole, lat=90°, altitude of polaris=90°

Polaris

How to find your latitude on Earth?

★


How to find your latitude on Earth?

Horizon

at the Equator, lat=0°, altitude of polaris=0°

Po

lar

is

★


Star Trails in between....

Mauna Kea, Hawai’i

20°

Altitude of North Star =

your latitude!


How to Find Polaris?


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


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


Seasons, Annual Motions, and Phases of the Moon


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.


SOHO Observes Solar Motion


What Time is It?

Possible times: sunset, sunrise, midnight, noonTuesday, August 31, 2010

What Time is It?

Possible times: sunset, sunrise, midnight, noon

6am: Sunrise


What Time is It?


12pm: Noon

6am: Sunrise


What Time is It?


6pm: Sunset

12pm: Noon

6am: Sunrise


What Time is It?


6pm: Sunset

12pm: Noon

6am: Sunrise

12am: midnight


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.


http://www.pfm.howard.edu/astronomy/Chaisson/AT401/IMAGES/AACHCIR0.JPGTuesday, August 31, 2010

http://www.pfm.howard.edu/astronomy/Chaisson/AT401/IMAGES/AACHCIR0.JPG




http://www.nmm.ac.uk/server/show/nav.00500300l005001000Tuesday, 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


Ecliptic on Celestial Sphere

Earth’s axis tilted 23º with respect to orbit


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


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


The reason for Seasons


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)


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)✕


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


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.


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


http://localhost/~jdsmith/movies/reasonforseasons.swf

http://localhost/~jdsmith/movies/reasonforseasons.swf

Sunrise above the artic circle


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




✪

A BC D




✪

A BC D


Does the Orientation of Earth’s Axis Change with Time?

26,000 yrs!Tuesday, August 31, 2010

The Earth Moves like a Top: “Precession”


http://localhost/~jdsmith/movies/precessionearthaxis.swf

http://localhost/~jdsmith/movies/precessionearthaxis.swf

What sign are You?

“Signs” of the zodiac: designed to indicate which constellations the sun is in.

Precession of the Earth’s axis


What sign are You?

“Signs” of the zodiac: designed to indicate which constellations the sun is in.

Precession of the Earth’s axis


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


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!


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.


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


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


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.


Before you Sit - University of Toledo

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