Home > Concepts, Observing, Telescopes > 07/19/2021 – Ephemeris – How does your telescope’s image orientation compare to how it looks to the naked-eye?

07/19/2021 – Ephemeris – How does your telescope’s image orientation compare to how it looks to the naked-eye?

July 19, 2021

This is Ephemeris for Monday, July 19th. Today the Sun will be up for 15 hours and 6 minutes, setting at 9:22, and it will rise tomorrow at 6:16. The Moon, 2 days past first quarter, will set at 2:35 tomorrow morning.

When you look through a telescope at the Moon, how does it look compare to how it looks to the naked-eye? Yes, it’s bigger and probably brighter. But how did its orientation change? Astronomical telescopes generally give an upside-own image, that is rotated 180 degrees. Newtonian reflector telescopes, with their eyepiece near the top of the telescope, give such an image, as do refractor telescopes where the diagonal mirror near the eyepiece is not used. When such a mirror is used a right side up, but mirror image is the result. The mirror image results when an odd number of reflections occur in the light path. Binoculars use two or four reflections. Newtonian reflectors have two reflections. It can be confusing sometimes.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hr). They may be different for your location.

Addendum

Telescope image orientations

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