The Telescope: A Unit Study

The Telescope: A Unit Study
Edwin Hubble

The astronomer Edwin Hubble, born November 20, 1889, is best known for having proven the existence of other galaxies besides our own, which made astronomers realize that the universe is significantly larger than they had previously thought. Hubble reached this discovery using some of the largest telescopes of his time. In light of all this, what could be more fitting than that the best telescope the world has ever seen be named after him? The Hubble Telescope is used for exploring the far-away galaxies that its namesake discovered.

The Telescope: A Unit Study
Refractor Telescope

The invention of the telescope is generally credited to Galileo, but telescopes were actually first invented by Hans Lippershey. Lippershey’s telescope was a refractor telescope with two lenses, a convex objective lens and an eyepiece, concave in shape. This is the type of telescope Galileo used one year later in 1609.

The Telescope: A Unit Study
Reflector Telescope

Newton designed the reflector telescope in 1668, which used a mirror to reflect and concentrate light onto another mirror, sending the now focused image to an eyepiece on the side of the telescope housing. A later design placed a mirror in the middle of the telescope, reflecting the image back towards the main mirror. This mirror had a hole in the center, allowing for an eyepiece at the end of the telescope.

Significant improvements were still made, but were generally on the order of increasing ease of use. The mirrors used in reflector telescopes were improved by using reflective coatings that didn’t tarnish. The more accurate grinding of lenses and mirrors also helped significantly.

Resolution has always presented a problem. Longer telescope lengths can be used to remedy this problem, but can make the telescopes rather unwieldy and unstable. Better frameworks fixed the stability problems; and the use of reflector telescopes aided the situation as they can be manufactured shorter than refractor telescopes. But a point is reached where further increase in telescope resolution is pointless; the atmosphere limits resolution as it is practically a dirty lens in its own right. Now if only one could raise the telescope above the earth’s atmosphere….

The Telescope: A Unit StudyWith the advent of space travel, this dream was realized. The idea for a telescope, called the Hubble Telescope, was formed. This telescope was to be placed above the earth’s atmosphere, increasing resolution and range by being above all pollution and clouds of the atmosphere. It would send the information gleaned to earth via radio waves. The telescope itself was to be of the Ritchey-Chrétien design — a reflector telescope with two concave mirrors reflecting light back through the center of the telescope main mirror. This design was proposed in 1905 and differed from other designs in as much as there were two magnifying convex mirrors instead of one convex and another regular flat mirror to direct the light where desired. This helped make the images of stars, for example, rounder and remedied coma problems — the image is blurred and comet shaped — as well as spherical aberration. The telescope cost more and took longer to build than anticipated, and after being launched in 1990 the images showed the spherical aberration that the design was supposed to eliminate!

A Ritchey-Chrétien telescope requires special instruments called null detectors to test the curvature of the mirror. The manufacturer of the main Hubble mirror had used a custom-made null detector for the purpose. Unfortunately, they had assembled it wrong — a lens was off by 1.3 mm. This of course meant error. The manufacturer also tested the mirror with conventional null detectors as well as their custom-made one. These did show a flaw, but the company chose to ignore the results concluding that their custom null detector was more accurate. Either way, the Hubble telescope was none too useful, and it needed fixed. The only practical solution was to install a “COSTAR” — a bank of corrective optics. This solution was installed in space, and worked quite well, although it was eventually replaced with sensors designed to compensate for the error in the main mirror.

The Hubble telescope proved to revolutionize the world of astronomy, making gazing into the other galaxies Edwin Hubble discovered easier and more fascinating.


Further Investigation

Edwin P. Hubble
Biography from NASA.

Telescope History
Follow the links at the bottom to view the entire timeline from Lippershey in 1608 through Hobby-Eberly in 1997.

Explanation with diagram from the McDonald Observatory at the University of Texas.

Explanation with diagram also from the McDonald Observatory.

The History of the Hubble Space Telescope
From NASA.

A Chronology of the Hubble Space Telescope
Timeline from NASA.



Timeline: A History of Telescopes
Interactive from National Geographic that looks at the various telescopes used through time.

Telescope Simulator
Great interactive at the University of Nebraska-Lincoln that helps you to see what happens when you use lenses of different focal length, different eyepieces, or other variations.

Sliding Telescopes
Craft idea from Crayola for the youngest students.

Make Your Own Telescope
Easy-to-make idea from the Exploratorium.

How to Build a Telescope
More complicated plan for older students.  Lenses can be purchased inexpensively from these science suppliers.

Simple Telescopes
Easy-to-follow explanation on how to make your own with diagrams.

Worksheet: Telescopes
Nice resource for summing up.  Use the questions for narration prompts.

Planetarium for Your Computer {Free}
Find out what is in the night sky so that you’ll know what to look for with your telescope.



The Telescope by Thomas Nolan
Accessible public domain work explaining the construction of telescopes including the differences between reflecting and refracting telescopes.

Star Stories by Gertrude Chandler Warner
Free eBook download to help young ones become familiar with the constellations.  Link includes free Star Book download.


Unit Studies & Lesson Plans

Taking a Closer Look: Examining Light and Telescope
Great lesson plan from Northrop Grumman adaptable to all grades with four activities covering how telescopes work.  Worksheets with answer key and posters included.

How Telescopes Work
Lesson plan from the observatory at LSU that demonstrates the difference between reflecting, refracting, and compound telescopes.

Free Nature Studies: The Solar SystemFree Nature Studies: The Solar System
Lots of astronomy resources in this section of our free nature studies, including telescope and night sky helps.


Printables & Notebooking Pages

Hubble Space Telescope
Diagram for notebook.

Hubble Exploded
Parts diagram for notebook showing how it is assembled.

TelescopeTelescope Notebooking Pages
Simple pages for copywork, narrations, or wrapping up.