Stars

STARS ARE INCREDIBLY MASSIVE SPHERES OF GAS THAT EMIT ELECTROMAGNETIC RADIATION. 

In our galaxy there are over 400 billion stars.  Astronomers estimate there to be over 10 SEXTILLION (10 with 22 zeros after it!) stars in the observable universe!!!  As you may expect with so many stars in the universe, there is tremendous variety in the kinds of stars we have observed.  WE CLASSIFY STARS INTO GROUPS BASED ON THEIR PHYSICAL PROPERTIES.

PROPERTIES OF STARS

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SIZE

Stars vary in size from smaller than the Earth to 2,000 times more massive than the Sun. 

COMPARED TO OTHER STARS, THE SUN IS AVERAGE SIZE.

 

Temperature

Stars are also extremely variable in terms of temperature.  Spica, a very hot star has a surface temperature of 28,000 degrees Celsius.  Antares on the other hand has a surface temperature of only 2,000 degrees Celsius. 

COMPARED TO OTHER STARS THE SUN HAS AN AVERAGE TEMPERATURE

COLOR

A STARS COLOR IS DIRECTLY RELATED TO ITS TEMPERATURE:

  • HOTTER STARS ARE BLUE
  • COOLER STARS ARE RED

 

LUMINOSITY

LUMINOSITY IS A MEASURE OF A STAR'S BRIGHTNESS.  IT DEPENDS ON THE STAR'S SIZE AND TEMPERATURE.

  • LARGE HOT STARS ARE MORE LUMINOUS
  • SMALL COOL STARS ARE LESS LUMINOUS
 

ESRT PAGE 15:  THE H-R DIAGRAM

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THE H-R DIAGRAM IS A SCATTER PLOT OF IMPORTANT STARS.  THEY ARE ORGANIZED BY THEIR SIZE, TEMPERATURE, COLOR, AND LUMINOSITY.  WE MUST BE ABLE TO USE THIS CHART TO DESCRIBE THE DETAILS OF ANY STAR ON IT.

 

 

FINDING TEMPERATURE AND COLOR

  • TO FIND THE TEMPERATURE AND COLOR OF ANY STAR ON THE H-R DIAGRAM WE JUST NEED TO LOOK STRAIGHT DOWN TO THE X-AXIS.
  • EXAMPLE: THE SUN'S
    • TEMP = 5,800 DEGREES K
    • COLOR =  YELLOW

 

 

FINDING LUMINOSITY AND SIZE

  • TO FIND THE LUMINOSITY WE JUST LOOK OVER TO THE LEFT SIDE OF THE CHART.  YOU WILL MOST LIKELY HAVE TO ESTIMATE THE EXACT LUMINOSITY USING THE SCALE PROVIDED.
  • TO FIND THE SIZE OF THE STAR WE JUST LOOK OVER TO THE RIGHT SIDE OF THE CHART.  THIS IS A VERY INFORMAL MEASUREMENT, IT CAN ONLY BE USED TO TELL US IF THE STAR IS SMALL, AVERAGE, OR MASSIVE.
  • EXAMPLE:  THE SUN
    • THE SUN'S LUMINOSITY = 1
    • THE SUN IS NOT AT THE TOP OR BOTTOM OF THE SIZE LINE SO IT IS AN AVERAGE SIZE

FINDING GROUPS OF STARS

  • GROUPS OF STARS ARE LABELED IN BIG BOLD LETTERING ON THE CHART:
    • SUPERGIANTS, GIANTS
    • MAIN SEQUENCE
    • WHITE DWARFS
  • STARS NEAR THESE GROUP NAMES BELONG TO THE GROUP
  • EXAMPLE:  THE SUN
    • THE SUN IS A MAIN SEQUENCE STAR