Archive for April 18, 2019

04/18/2019 – Ephemeris – Tides

April 18, 2019 Comments off

Ephemeris for Thursday, April 18th. Today the Sun will be up for 13 hours and 37 minutes, setting at 8:31, and it will rise tomorrow at 6:52. The Moon, 1 day before full, will set at 7:22 tomorrow morning.

The Moon and the Earth gravitationally attract each other. And the Moon raises tides in the Earth itself and its oceans. The Earth’s tides on the mass of the Moon has slowed its rotation so it continually shows the Earth the same face. The Moon, only one 81st the mass of the Earth hasn’t been as successful at greatly slowing the Earth’s rotation. It does cause the world’s timekeepers to add one second occasionally to the time stream to offset our atomic clocks to the Earth’s rotation. The most noticeable effects of the Moon’s tidal force is the tides in the Earth’s oceans. The highest tides are when the Sun and Moon are in line with the Earth at new and full moon. Small bodies of water like the Great Lakes don’t have luni-solar tides greater than 2 inches (5 cm).  The Great Lakes do have tide like effects called seiches, like water sloshing in a bath tub, caused by wind or barometric pressure, and can be several feet high.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


This link from NOAA explains tides better than I can:

This link is the explanation of seiches:

Categories: Concepts, Ephemeris Program Tags: