A1 02 Celestial Sphere

The Celestial Sphere
LACC: §3.2, 3.5, 3.7
• Coordinates--Declination Latitude,
Right Ascension Longitude

• North and South Celestial Poles,
Celestial Equator, Ecliptic
• Using the stars to navigate

What is out there?

Wednesday, February 10, 2010

Earth Coordinates

http://www.passivesolarenergy.info/


Earth Coordinates

• North and South • axial tilt = 23.5°
poles • Arctic Circle, 66.5°N
• equator • Antarctic Circle, 66.5° S
• latitude • tropic of Cancer, 23.5° N
• longitude • tropic of Capricorn, 23.5° S


Celestial Coordinates

http://visual.merriam-webster.com/astronomy/astronomical-observation/celestial-coordinate-system.php


North Celestial Pole

http://astro.unl.edu/classaction/images/coordsmotion/startrails.html


Celestial Coordinates
• North and South • spring and autumnal
celestial poles equinox (20 Mar., 22
• zenith Sept.)

• meridian • summer and winter
solstice (21 June, 21
• celestial equator Dec.)
• ecliptic plane • right ascension [RA]
(Earth’s orbit, Sun’s
Path) • declination [dec]
http://astro.unl.edu/classaction/animations/coordsmotion/radecdemo.html
Celestial-Equator (RA/Dec) Demonstrator
http://astro.unl.edu/classaction/animations/coordsmotion/celhorcomp.html
Rotating Sky Explorer
Los Angeles: Latitude: 34° 05', North. Longitude: 118° 22', West


Navigation
If you know the declination of an object, and you
measure it’s altitude when it’s on the meridian, then you
can determine your latitude.
Finding latitude with the Pole Star

Imagine yourself standing at night at point P on
Earth and observing the pole star (or better, the
P
position of the north celestial pole, near that star),
at an elevation angle λ above the horizon.

The angle between the direction of the pole and
the zenith is then (90°–λ) degrees. If you continue
the line from zenith downwards (see drawing) it
reaches the center of the Earth, and the angle
between it and the Earth's axis is also (90°–λ).

Therefore (as the drawing shows) λ is also your
latitude.
http://www-istp.gsfc.nasa.gov/stargaze/Snavigat.htm


Movement of the
Celestial Sphere
The celestial sphere isn’t what is moving. (Of
course, a spherical shell of stars doesn’t even
exist.) The earth rotates inside of it.
Objects in space appear to “rise in the East and
set in the West”. One can imagine why people
thought the Earth was ﬁxed in space, and the
celestial sphere rotated around it--we don’t feel
the Earth rotating. Actually, the earth’s rotation
makes it appear that objects in space move from
east to west over the course of the day and/or
night.
Imagine a globe inside a celestial sphere.

AstroTeam Classwork
• Fill in this table with these four answer choices:
latitude | longitude | right ascension | declination
North/South East/West
Location Location
Earth’s Surface
Celestial Sphere

• You wake up with no memory of who or where you
are, but it is night and you recognize the North Star
(Polaris, the star in the tail of the Little Dipper). If the
Polaris is at zenith, where are you? What if it is on
the horizon? What if it is at an altitude of 23.5°?


LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch. 3, pp. 82-83: 1, 9.

Due on the ﬁrst class of the following week, at the
beginning of class.


Celestial Mechanics
LACC: §3.2, 3.5, 3.7

• Marking Time: day rotation, year
revolution
• Effects of the Sun: solar vs. sidereal, seasons
• Changes in the Sky: Moon Phases, Eclipses

What is going on out there?


Time -- Time Zones


Time -- Days

Sidereal Day Solar Day

23h 56m 4.09s 24h

The time The time
between a between our
star’s zeniths sun’s zeniths


Time--Year and Seasons

http://visual.merriam-webster.com/
earth/meteorology/seasons-year.php

http://astro.unl.edu/classaction/animations/coordsmotion/transitmovie.html
Time-Lapse Season Demonstrator

http://astro.unl.edu/classaction/animations/coordsmotion/daylighthoursexplorer.html
Daylight Hours Explorer

http://astro.unl.edu/classaction/animations/coordsmotion/eclipticsimulator.html
Seasons and Ecliptic Simulator


The Earth-Moon System:
Moon Phases

http://www.astrosociety.org/education/
publications/tnl/12/12.html

http://astro.unl.edu/classaction/animations/lunarcycles/lunarapplet.html
Lunar Phase Simulator
http://astro.unl.edu/classaction/animations/lunarcycles/moonphases.html
Three Views Simulator


Lunar Eclipses

http://hyperphysics.phy-astr.gsu.edu/
hbase/solar/lunecl.html

http://astro.unl.edu/classaction/animations/lunarcycles/eclipsetable.html
Eclipse Table


Lunar Eclipses

http://astro.unl.edu/classaction/images/
lunarcycles/lunareclipse.html

http://astro.unl.edu/classaction/images/
lunarcycles/lunareclipse2004.html


Solar Eclipses

http://astro.unl.edu/classaction/images/lunarcycles/ http://astro.unl.edu/classaction/images/
solareclipse.html lunarcycles/solareclipse1999.html

http://astro.unl.edu/classaction/images/lunarcycles/ http://astro.unl.edu/classaction/images/
solareclipse2.html lunarcycles/solareclipse1994.html


Solar Eclipse

http://astro.unl.edu/classaction/images/lunarcycles/solareclipse1999mir.jpg


AstroTeam Classwork

• What are two ways the 23.5° tilt of the Earth’s
axis causes summers in the United States to
be warmer than the winters? (Voyages, Ch. 3,
pp. 82-83: 5)

Due presently.


LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch. 3, pp. 82-83: 11, 16.

• Ch 4: Tutorial Quizzes accessible from:
www.brookscole.com/cgi-brookscole/course_products_bc.pl?
http://

ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19

Due on the ﬁrst class of the following week, at the
beginning of class.


A1 02 Celestial Sphere

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A1 02 Celestial Sphere