Discovering

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CHAPTER 1 Discovering the Night
Sky Constellations,Asterisms and the Celestial
Sphere
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WHAT DO YOU THINK?

• Is the North StarPolaristhe brightest star in
  the night sky?
• Do astronomers regard constellations as the
  familiar patterns of stars in the sky?

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Constellations Finding our place in the sky
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Describe the Nature and Use of Constellations

• Constellations make star locating easy.
• Constellation a region and a group of stars
• Night sky is divided into 88 regions
  (constellations)
• Astronomers, requiring more accuracy, now use a
  coordinate system as well (right ascension and
  declination see the celestial sphere)

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In order to more easily locate objects in the
sky, we divide the sky into regions named after
familiar patterns of stars called constellations.

Ancient constellations were imaginary pictures
outlined by familiar patterns of stars.
Modern astronomers divide the sky into 88
official constellations or regions of space, many
of which contain the ancient star patterns.
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Some Common Guides to Finding Constellations
Using the Big Dipper as a guide
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The Summer Triangle
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The Winter Triangle
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Starry Night Exercise

• Chapter 1 Stars and Constellations

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Locating your position on Earth

• Earths coordinate system uses a series of grid
  lines that circle the globe N-S and E-W and
  that intersect at right anglesThese grid lines
  are called
• longitude (north-south)
• latitude (east-west)

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Labeling one hemisphere

• Latitude
• Longitude
• Zenith
• Horizon
• Meridians and parallels
• Prime meridian
• Equator
• Label your plastic hemisphere

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Latitude vs. Longitude
http//www.hammondmap.com/sites/hammond/geography/
latlong1.html
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What is the approximate latitude and longitude
for Fort Thomas, KY?
http//www.nasa.gov/
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• The latitude of Fort Thomas is 39.075N. The
  longitude is 84.447W.

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Locating your position in the sky

• Rise and run above the Earths surface are
  called
• Altitude (0-90o) starts at the horizon, ends at
  zenith
• Azimuth (0-360o) starts at due north

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http//meteorites.pdx.edu/measurements.htm
http//geology.isu.edu/geostac/Field_Exercise/topo
maps/bearing.htm
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Starry Night Exercise

• Chapter 2 Changing Latitude

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The Celestial Sphere
to envision the night sky rotating eastward like
the outer shell of a hollow sphere...
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Celestial Sphere

• The celestial sphere aids in navigating the sky
• Earth-based view
• A coordinate system (it works on the principle of
  latitude-longitude and altitude-azimuth)
• Declination
• Right ascension

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Relationships between the three coordinate systems

• Declination is related to altitude and latitude
• Right ascension is related to longitude and
  azimuth

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Astronomers describe the universe as an imaginary
sphere surrounding the earth on which all objects
in the sky can be located, called the CELESTIAL
SPHERE.

• As viewed from Earth, the celestial sphere
  appears to rotate around two axis points, the
  north and south celestial poles, which are
  located directly above the Earths poles.
• Between these is the celestial equator, which
  divides the celestial sphere into northern and
  southern hemispheres.
• We define the position of an object on the
  celestial sphere using two coordinates, right
  ascension and declination.

See animation 1.1 and interactive exercise 1.1
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Starry Night Demo

• Turn on celestial grid, turn off horizon
• Note the coordinates listed for each grid line

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Angular Diameter and Distance

• Used to describe the apparent size of or distance
  between astronomical objects.
• Uses degrees, arcminutes and arcseconds.
• Example of a measurement 60o 30 3

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Usage of Angular Diameter

• Size of an object (Sun and Moon have very similar
  angular diameters0.5o degrees or 30 arcminutes)
• Distance between objects
• Distance object traveles
• True diameter (calculated)

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Ecliptic Plane on the Celestial Sphere

• The annual path of the Sun as it appears on the
  celestial sphere.
• The ecliptic and the celestial equator are tilted
  at a 23 ½-degree angle
• Earth orbits the Sun while tilted at a 23 ½-
  degree angle.
• Starry Night Demo the celestial sphere and the
  ecliptic plane

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Starry Night Celestial Sphere

• Open Starry Night program
• Go to Options/Guides/celestial grid, pole,
  meridian, zenith
• Go to observing/diurnal/diurnal a
• Go to earths orbit/orbit a
• Go to seasons/view over south pole

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What's Your Sign?
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One effect of this motion is to change the
location in the Earths orbit at which summer and
winter occur, and thus change the time of year
when the Sun appears in certain constellations.
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Astrology Table

• Pisces - February 20- March 20
• Aries - March 21 - April 20
• Taurus - April 21 - May 21
• Gemini - May 22 - June 21
• Cancer - June 22 - July 22
• Leo - July 23 -August 21
• Virgo - August 22 - September 23
• Libra - September 24 - October 23
• Scorpio - October 24 - November 22
• Sagittarius - November 23 - December 22
• Capricorn - December 23 - January 20
• Aquarius - January 21 - February 19

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We can see how different stars appear at
different times of day by looking at the position
of the Sun against the backdrop of stars. The
side of the Earth facing the Sun is experiencing
day, while the side of the Earth turned away
from the Sun is experiencing night.
MARCH
SEPTEMBER
(The Sun is in Virgo)
(The Sun is in Pisces)
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Zodiac Activity

• Select one of 13 zodiac constellations.
• Use the Starry Night Program to find your zodiac
  constellation
• Draw your zodiac constellation to scale.
• Label the stars in your constellation.
• Classroom demonstration using lamp as the Sun
• Questions
• Explain what it means for the Sun to be in your
  zodiac constellation.
• When is your zodiac constellation visible?

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Stars in 3-D

• Activity F-8 Three-Dimensional Constellations
• How far away from the Earth are these stars?
• Is the brightness of stars an indicator of
  distance? Explain.
• How would these constellations appear in
  different places in space?

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Student Activities

• Chapter 1 Stars and Constellations
• Chapter 2 Changing Latitude
• Starry Night Demos
• Zodiac activity
• 3-d stars
• Observing project
• Questions
• Research option

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• http//www.whfreeman.com/dtu7e