PES 105        Fall 2001 Previous Lecture General Astronomy I Next Lecture

Lecture Notes:

Observations, Constellations and Coordinate systems

text: Chapter 1 Section 1

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Scientific Notation

To express numbers over a large range (like those describing distances in the solar system), we use scientific notation (powers of 10).

1.62 x 10⁵ = 162,000 ............... 10⁵ means move decimal point 5 places to right

1.62 x 10^-5 = 0.0000162 ........... 10^-5 means move decimal point 5 places to left

A Scientific Notation exercise is available at: http://janus.astro.umd.edu/astro/scinote.html

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Observing from Earth

Stars seen in the Northern Hemisphere are NOT the same as those seen in the Southern Hemisphere.

Here is another picture showing visibility of stars in the Northern Hemisphere: http://www.stark.kent.edu/~aheinrich/chaprev/celrot01.htm

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Constellations

definition: groups of stars that people associate names with

See Figure 1.3 and see if you can see the names in the stars ! Here is a link to the figure.

12 constellations along the zodiac ("zodiac" = "zoo")

most are named after animals

See Figure 1.5 for the constellations of the zodiac. Here is a link to the figure.

Different cultures assigned different names to the same groups of stars

constellation link with lots on information: http://www.astro.wisc.edu/~dolan/constellations/

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Celestial Sphere

For observation - we can ignore distance

=> assume all objects are at the same distance

=> everything is on a big sphere around the Earth ......... the "celestial sphere"

See Figure 1.2 of Celestial Sphere concept. Here is a link to the figure.

See Figure 1.4 for more detailed image of Celestial Sphere. Here is a link to the figure.

Path of the sun is NOT along the celestial equator.

Since the Earth's rotation axis is tilted 23.5 degrees, the Sun follows a path which is tilted 23.5 degrees from the equator.

Path of the sun on the celestial sphere = "ecliptic"

Two points exist where the Sun's path (ecliptic) crosses the celestial equator

=> Sun is directly overhead at Earth's equator

=> 12 hours of day and 12 hours of night

call these points the "equinoxes" ..... equinox = "equal night"

we use the vernal equinox as the origin of a coordinate system for locating the stars

link to another picture of the celestial sphere: http://zebu.uoregon.edu/~imamura/121/images/sphere.gif

link to animation showing how the stars change position in the sky over the course of a night: http://inkido.indiana.edu/a100/celestialsphere7.html

link to a very nice picture and description of the celestial sphere: http://wind.cc.whecn.edu/~marquard/astronomy/celestial_sphere.htm

link to a very complete discussion of the celestial sphere: http://online.bc.cc.ca.us/sea/astronomy/nakedeyeb/neyein.htm

Here is an animation showing the celestial sphere as viewed from different lattitudes: http://online.bc.cc.ca.us/sea/astronomy/nakedeyeb/csph1t5.htm . . . (This one takes a little study . NCP = North Celestial Pole.)

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