Listed following are the names and mirror diameters for six of the world’s greatest reflecting telescopes used to gather visible light. Rank the telescopes from left to right based on their light-collecting area from largest to smallest. For telescopes with more than one mirror, rank based on the combined light-collecting area of the mirrors.

- Large binocular telescope with two 8.4 m mirrors
- Keck 1 one 10 - m mirror
- Hobby-Ebberly one 9.2-m mirror
- Subaru one 8.3 m mirror
- Gemini North one 8-m mirror
- Magellan 2 one 6.5 m mirorr

Large binocular telescope, Keck 1 telescope, Hobby-Ebberly telescope, Subaru telescope, Gemini North telescope, Magellan 2 telescope

Explanation:

How much light a telescope can collect depends on its diameter, since in a bigger area more photons will be collected.    

Remember that in a circle the area is defined as:

 (1)

Where A is the area and r is its radius.

However, the radius can be determined by means of its diameter.

(1)

Where d is its diameter.

An example of this is when a person is collecting raindrops with a bucket and with a cup. Since the bucket has a bigger area than the cup, it will collect more raindrops by unit of time. In this scenario the raindrops represent the photons.  

To determine the light collecting area of each telescope, equation 2 will be replaced in equation 1.

 (3)

Case for Large binocular telescope:

For the second mirror will be the same value

Case for Keck 1 telescope:

Case for Hobby-Ebberly telescope:

Case for Subaru telescope:

Case for Gemini North telescope:

Case for Magellan 2 telescope:

Hence, they may be rank in the following way:

Large binocular telescope, Keck 1 telescope, Hobby-Ebberly telescope, Subaru telescope, Gemini North telescope, Magellan 2 telescope.

Key term:

Photons: particles that constitute light.