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06/16/2023 – Ephemeris – Twilight is longer near the summer solstice

June 16, 2023 Comments off

This is Ephemeris for Friday, June 16th. Today the Sun will be up for 15 hours and 33 minutes, setting at 9:30, and it will rise tomorrow at 5:56. The Moon, 2 days before new, will rise at 5:04 tomorrow morning.

Not only does the Sun set later this time of year, but twilight lasts longer too. As of tonight the end of astronomical twilight, when the last vestiges of twilight are gone is, for the Traverse City/Interlochen area, 12:01 am, That’s two and a half hours of evening twilight. I feel that for most purposes that the end of nautical twilight, when navigators on ships could no longer see the horizon for their sextant readings, is dark enough to view most stars, and brighter objects beyond the solar system, what we call deep sky objects. That happens at 10:56 pm, or about an hour and a half after sunset. Twilight of both kinds are a third shorter around the equinoxes. These times are dependent on our latitude, and the Sun’s declination which is equivalent to latitude.

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

Addendum

A comparison of the Sun’s path below the horizon after sunset. The Sun is shown at 15 minute intervals. The Sun at the summer solstice is moving slower due to the fact that it’s at 23 1/2 degrees north of the celestial equator where the it is on an equinox. Note also that the angle of the solstice path starts to level off near the end of the path as it approaches the north direction. Diagram created using my LookingUp app and LibreOffice Draw for captions.

Check out my September 27, 2018 post about the different twilight periods.

09/27/2018 – Ephemeris – Twilight zone
Categories: Concepts, Ephemeris Program, Twilight Tags: