A few applications of large optical  telescopes are stargazing and astronomical research. A few of the most  famous optical telescopes are the Hubble Space Telescope and the  telescope at the United States Naval Observatory in Washington, D.C.  which discovered Mars’ moons Phobos and Deimos (What Are Optical Telescopes Used For?, n.d.).  

“The Hubble Space Telescope is a Cassegrain reflector telescope. That  just means that light enters the device through the opening and bounces  off the primary mirror to a secondary mirror. The secondary mirror in  turn reflects the light through a hole in the center of the primary  mirror to a focal point behind the primary mirror” (How Hubble Space Telescope Works, 2000).  Below is a photo of the Hubble Space Telescope. 

Telescopes that utilize mirrors are known  as reflector telescopes. These mirrors are placed specifically inside  the telescope to gather and focus light to the eye piece. Due to this  process, reflector telescopes perform well in low-light situations.  Other advantages of mirrors are that they are lighter, and easier to  make completely smooth (NASA, 2019).  

References: 

What Are Optical Telescopes Used for? (n.d.). Sciencing. https://sciencing.com/optical-telescopes-used-for-6370484.htmlLinks to an external site. 

How Hubble Space Telescope Works. (2000, December 1). HowStuffWorks. https://science.howstuffworks.com/hubble.htm#:~:text=Specifically%2C%20Hubble%20is%20a%20Cassegrain%20reflector%20telescope.%20ThatLinks to an external site. 

NASA. (2019). How Do Telescopes Work? | NASA Space Place – NASA Science for Kids. Nasa.gov. https://spaceplace.nasa.gov/telescopes/en/Links to an external site.