Hi There !

Last night, I was on a jet flying due west
as the sun was setting.  I assume the airplane
was going 400-600 MPH at 35,000 feet.

The sun was balanced on the horizon, half in view
and half out of view.  Because we were heading
west, the sun took a very long time (40-60 minutes)
to set.

This same sunset would have occurred in 5-15 minutes
on the ground.

A 5-star answer would be the speed required for an
jet aircraft, such that the sun would seemingly rise in the west.

Approximate speed is fine with me.  No "heavy lifting" mathematics
required.

All comments greatly appreciated !

ron

Hello again Ron,

Interesting question (but then again, ALL your questions are
interesting questions.  Strange.  But interesting.)

The setting sun "travels" around the circumference of the earth in 24
hours.  In other words, it travels 25,000 miles in 24 hours, or a bit
over 1,000 miles an hour.  Travel west any faster than that, and you
will "reverse" the sun's direction, and it will rise in the sky,
rather than set.


Put it another way, when the sun sets in my hometown of Washington DC,
it still has three hours yet before it sets in Los Angeles, about
3,000 miles away.

If I could hop on the recently-departed Concorde and fly across the
country at 1,000 miles an hour, I'd land in LA thee hours later, just
as the sun was setting -- the same position in the sky as when I left
DC.

Travel a bit faster than 1,000 mph,and I arrive at the west coast in
under three hours -- the sun will actually be higher in the sky when I
land in LaLa land.

Kapish?


Any questions, just fire away.

paf

pafalafa,

If you think my questions are strange and interesting, you should see
my face !     heh  heh  heh

Excellent and straightforward answer.

Thank you.
ron

Jerry Glasser and Ted Ross once took off after sunset in an SR-71.
They flew a westerly course, and, since the day/night terminator
travels at only about a thousand miles per hour at the equator, and
since the supersonic spy plane travels much faster than that, they
watched the sun "rise" in the west. After a while, they turned south,
and the sun set again. Later in the mission, they headed west again,
and observed the sun slowly rise over the horizon. Glasser and Ross
may be the only people to see the sun rise in the west. Twice in one
"day."

http://www-psao.grc.nasa.gov/asao.quiz/october.97.html

Thanks, pinkfreud.  I appreciate your comments !

ron

Keep in mind that the tangent speed of Earth's rotation varies with
latitude. It's roughly 1,000m/h at the equator, but drops steadily and
approaches zero as one approaches either of the poles. So accordingly,
the ground speed of an aircraft keeping the Sun balanced at a fixed
angular separation will also vary in the same way. Near the south
pole, for example, you'd be able to crawl fast enough to keep the Sun
at a fixed angular separation from you.

-Mark Martin

Thanks, Mark.  Very elegant exposition.

Quod erat demonstrandum!
ron