Left pointing hand navigation decoration
( ! ) Notice: Undefined index: HTTP_REFERER in /local/data1/hosts/as/htdocs/resources/explorations/groundup/library/return.php on line 88
Call Stack
#TimeMemoryFunctionLocation
10.0001237160{main}( )../term-full.php:0
20.0058389400returnLink( )../term-full.php:41

( ! ) Warning: file_get_contents(): Filename cannot be empty in /local/data1/hosts/as/htdocs/resources/explorations/groundup/library/return.php on line 91
Call Stack
#TimeMemoryFunctionLocation
10.0001237160{main}( )../term-full.php:0
20.0058389400returnLink( )../term-full.php:41
30.0058389624file_get_contents ( )../return.php:91

( ! ) Notice: Undefined variable: title in /local/data1/hosts/as/htdocs/resources/explorations/groundup/library/return.php on line 94
Call Stack
#TimeMemoryFunctionLocation
10.0001237160{main}( )../term-full.php:0
20.0058389400returnLink( )../term-full.php:41
Return to “Telescopes from the Ground Up” Left pointing hand navigation decoration
Telescopes from the Ground Up

Focal point

The focal point of a lens or mirror is the point in space where parallel light rays meet after passing through the lens or bouncing off the mirror. A "perfect" lens or mirror would send all light rays through one focal point, which would result in the clearest image.

Diagram of how a perfect lens creates a focal point.

( ! ) Notice: Undefined index: HTTP_REFERER in /local/data1/hosts/as/htdocs/resources/explorations/groundup/library/return.php on line 88
Call Stack
#TimeMemoryFunctionLocation
10.0001237160{main}( )../term-full.php:0
20.0117389600returnLink( )../term-full.php:49

( ! ) Warning: file_get_contents(): Filename cannot be empty in /local/data1/hosts/as/htdocs/resources/explorations/groundup/library/return.php on line 91
Call Stack
#TimeMemoryFunctionLocation
10.0001237160{main}( )../term-full.php:0
20.0117389600returnLink( )../term-full.php:49
30.0117389784file_get_contents ( )../return.php:91

( ! ) Notice: Undefined variable: title in /local/data1/hosts/as/htdocs/resources/explorations/groundup/library/return.php on line 94
Call Stack
#TimeMemoryFunctionLocation
10.0001237160{main}( )../term-full.php:0
20.0117389600returnLink( )../term-full.php:49
Return to “Telescopes from the Ground Up”