When did Isaac Newton build his first reflecting telescope?
Newton built his first reflecting telescope in late 1668. He first wrote about it in a letter dated the 23rd of February 1669, addressed to Henry Oldenburg, Secretary of the Royal Society.
Questions about Newton's reflector
Short answers, pulled from the story.
Why did Newton build a reflecting telescope instead of a refracting one?
Newton built a reflecting telescope to prove his theory that white light is composed of a spectrum of colours. He concluded that any refracting telescope lens would inevitably split light into colours, causing chromatic aberration, and that mirrors could bypass this problem entirely.
What metal did Newton use to make the mirror in his reflecting telescope?
Newton cast the mirror from a custom alloy of six parts copper to two parts tin, an early composition of what became known as speculum metal. He devised his own methods for grinding and polishing the mirror surface.
How powerful was Newton's reflecting telescope?
Newton's second telescope, the one presented to the Royal Society, magnified 35 times by his own measurement. It had a primary mirror 2 inches in diameter with a focal length of 6.25 inches, and an eyepiece with a focal length of approximately 4.5 millimetres.
Who helped Newton build his third reflecting telescope?
Newton built his third telescope in 1671-1672 with his chamber-fellow at Trinity College, John Wickins. Newton noted that Wickins did a better job of figuring the mirror than Newton had managed on his second telescope.
Is the telescope the Royal Society displays today actually Newton's first telescope?
No. The telescope held by the Royal Society is almost certainly Newton's third telescope, built in 1671-1672 with John Wickins. A plaque added at a later date incorrectly identifies it as Newton's first telescope made in 1671. The mirror in the current instrument contains arsenic, a modification Newton proposed only after completing the second telescope, which identifies it as a later instrument.