YSI 1995 / Reporting Groups / Photometry

Students: LaShawn Dupree, Cory Cook,and Will Smith

Photometry: Measuring the Brightness of the Stars

BY: LaShawn Dupree, Cory Cook,and Will Smith

Advised by: Mr. Todd Duncan, Mr. Al Harper, and Ms. Chicha Tenner


Hello my name is Will Smith and the other members of my group is LaShawn Dupree and Cory Cook. Today we will be talking to you about photometry and how it works.

There are many ways that you can measure the brightness of stars. You can use eyes to measure the brightness, but in our project we used a more accurate device called a Photoelectric Photometer. This device converts the light that we see into electricity. In experiment we learned how our eyes respond to light of different brightness.

We also made comparisions of the brightness of different stars determining how much energy we received from them. The experiment was done and we came out with accurate results.


Early sky watchers developed a system for classifying stars on the basis of how bright they looked. The brightest stars were referred to as stars of the 1st magnitude, and the next brightest was second magnitude and so on. Astronomers classification has developed into the very precise magnitude system use today.

There are two types of magnitudes, apparent and absolute magnitude. Apparent magnitude is how an bright object appears to an earth based observer. Apparent magnitude does not tell you the actual brigtness.

Absolute magnitude is the apparent magnitude that a star would have if it were located at a distance of exactly ten porsecs from the earth.

Luminosity is related to absolute magnitude, it's the amount of energy escaping from a star's surface each second.


In conclusion our group learned how to measure the brightness of stars, and determine the stars magnitude. We learned how to do this by learning how to use a Photoelectric Photometer. Using this device we learned that the brighter a star, the higher the magnitude is. When using the photometer if it is expose to too much light it will not harm it but the photometer will shut off and go back to zero.

Because of a cloudy night we were only able to see the Moon, Jupiter, and the Summer Triangle for a short period of time. Out of these heavenly bodies we discovered that Jupiter had an higher magnitude than deneb. We also learned that because the moon's light was so bright that the photometer did shut off as suggested. Although the class was short and the clouds kept playing peek-a-boo with us, we enjoyed and learned alot about photometry.

Captions from board

WHAT IS MAGNITUDE ? Magnitude is a system use for classifying stars according to the brightness of the star.

WHAT IS PHOTOMETRY ? Photometry is measuring of the brightness of stars.

WHAT IS LUMINOSITY ? Luminosity is the amount of energy escaping from a star's surface each second.

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