Universe Cycle - Universe (3)
 Lab 

   
OBJECTIVES:
  • Exploring components of a galaxy.
  • Comparing and contrasting stars.
VOCABULARY:
  • absolute brightness
  • absolute magnitude
  • apparent brightness
  • apparent magnitude
  • helium
  • hydrogen
  • light
  • star
MATERIALS:

Students study the stars using a celestial globe.

BACKGROUND:

Stars are a fundamental component of galaxies. In the lower grades students learned a simple classification of objects in the Universe: those bodies in space that make light, and those that reflect light. A star is an object that makes light, because much energy released when hydrogen fuses, or "burns" to form helium.

There are many different types of stars. Stars are classified by their color, which corresponds to their temperature. Blue stars are extremely hot, 7,500E to over 25,000E Kelvin (273.16E Kelvin = 0E centigrade). White stars are cooler (6,000E - 7,500EK), yellow stars range from 5,000E to 6,000EK; orange stars range from is 3,500E to 5,000EK and red stars are less than 3,500EK.

When we look at stars in the night sky, we do not see them as they really appear, because they are at greatly varying distances from Earth. From Earth we see each starís relative brightness. For example, a dim nearby star might appear brighter and bigger than a faraway very bright star. In contrast, if the stars were all the same distance from Earth, we would see their absolute brightness. Bright stars would always look brighter than dim stars.

Astronomers call a star's brightness its magnitude. The brightness as we see it on Earth is termed apparent magnitude, while a starís actual light output is called absolute magnitude. For instance our Sun has an apparent magnitude of -26.8 (very bright) but an absolute of 4.8 (not bright). The derivation of these numbers is not important in the third grade. The main point is that from Earth, we see only the apparent brightness of the stars.

Astronomers group and name stars using their locations and brightness. We usually think of grouping stars in constellations, but these are artificial, historical associations which have little to do the real magnitude and locations of stars. The main stars in each constellation are labeled with a letter of the Greek alphabet, the brightest in the group is usually termed alpha. The rest of the Greek alphabet is usually used to label lesser brightness. Many stars are not even in constellations. These are named with numbers.

LETTERS OF THE GREEK ALPHABET

alpha

iota

rho

beta

kappa

sigma

gamma

lambda

tau

delta

mu

upsilon

epsilon

nu

phi

zeta

xi

chi

eta

omicron

psi

theta

pi

omega

In this lab, students will use the inflatable celestial globes to find several constellations. This will help them develop a sense of star brightness and to learn how to locate stars in the sky. Many details on the globe are too difficult for this grade. The following information, however, is enough to allow the students to successfully use the globes.

The area where you blow air into the globe is the location of the North Star, commonly called Polaris. It was discovered early on that the night sky (only in the northern hemisphere) seems to revolve around at fixed northern point; the star closest to this location came to be called the North Star. Navigators used the North Star to guide ships and caravans while traveling at night. The height of the North Star above the horizon depends on the latitude at which you live. The North Star is 40E above the horizon for most of the continental United States.

If your students have trouble understanding that we revolve around the North Star you can use an umbrella to illustrate this point. Open the umbrella and draw two constellations on it with a piece of chalk, or use glow-in-the dark stickers. Spin the umbrella. The spinning represents movement of the constellations around a central point which simulates the North Star.

The line labeled 0E on the globe is the celestial equator. This is a projection into space of the Earthís equator. The months of the year are written on the celestial equator. This indicates what celestial objects are visible each month. The northern part is for the northern hemisphere and the southern is for the people that live south of the equator. Remember they see stars at a different angle than the United States. For example, they do not see the North Star.

The 88 recognized constellations are enclosed within dotted lines on the celestial sphere. These constellations help astronomers create sectors, so they can locate other stars. Remember there are constellations that can only be seen in the northern hemisphere and only in the southern hemisphere.

PROCEDURE:
  1. Give students a celestial globe. Point out the location of the North Star and the celestial equator (0E) to the students. Explain the different symbols on the celestial globe by using the information provided below.
magnitude the larger the circle the brighter it appears to us on Earth       
double or multiple stars

variable star

open cluster

globular cluster

galaxy

diffuse nebula

planetary nebula

letter and then number galaxy names
east/west lines represent the declination from the real equator
north/south lines represent time during the year
dotted lines with names boundaries of the constellations, total of 88
dotted lines without names represent either galactic equator or ecliptic
Greek alphabet helps identify a star, used like a first name
numbers refer to stars
  1. Students may ask how far away the stars are located. Explain that the distances are unimaginable. Astronomers invented their own unit to measure these distances called the light year. This is the distance a beam of light travels in one year, about 9.46 trillion kilometers.
      
  2. Have the students look at the celestial globe to find the different star patterns and complete the worksheet. This exercise will take students a long time to complete individually, so you may want them to work in groups. The more the students look at the globe, the more it will make sense to them.
      
  3. The illustration below shows the answers at which the students should arrive.

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