Sunday, August 07, 2011

Dawn at the equator

I recently returned from my first-ever visit to the Amazon.  One thing that I noticed right away was the abrupt rising and setting of the sun.  It goes straight up or down, quickly.  This felt, upon my arrival from summer in Maryland, where evenings are long and sunlight lingers, like the flipping of a light switch.  I have an interest in naked-eye astronomy, and one of my favorite books is Aveni's "Skywatchers of Ancient Mexico."  I have the 1980 edition.  A revised and updated version, simply "Skywatchers," was released in 2001.

To an observer on the equator, the sun appears to rise and set straight up,
but does move to the north and south through the year.

The last time I was on the equator was in 1997 or so, when I visited the Galapagos.  Being on a boat made astronomical observations difficult.  This time, I stayed with Janet in Belem, in the hotel Grão Pará.  On our second day we moved to a room on the top floor, with an outstanding view of the city.

The Belem skyline from the Hotel Grão Pará
on Av. Presidente Vargas, overlooking the Praça da República

From this vantage point, it was possible to document the movement of the sun from north to south by observing the position of sunrise on three consecutive days.

The southward movement of sunrise over three days in July.

Sunrise, July 17
Sunrise, July 18
Sunrise, July 19

I was also able, on July 19, my last day, to capture evidence that the sun rises straight up (even though it is not rising due east).

6:43 am
6:44 am
6:48 am

As it rose from behind a building, it peeked out through consecutive aligned openings. If it had been moving left to right, it would not have been seen through more than one of these.


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