Explanation:
When does the line between day and night become vertical?
Tomorrow.
Tomorrow is an
equinox on planet Earth,
a time of year when day and night are most nearly equal.
At an equinox, the
Earth's terminator --
the dividing line between day and night -- becomes vertical and connects the
north and
south poles.
The above time-lapse video
demonstrates this by displaying an entire year on planet Earth in twelve seconds.
From geosynchronous orbit, the
Meteosat satellite recorded
these infrared images
of the Earth every day at the same
local time.
The video started at the
September 2010
equinox with the terminator line being vertical.
As the
Earth revolved around the Sun, the
terminator was seen to tilt in a way that provides less daily sunlight
to the northern hemisphere,
causing winter
in the north.
As the year progressed, the
March 2011
equinox arrived halfway through the video, followed by the terminator tilting the other way,
causing winter
in the southern hemisphere -- and summer in the north.
The captured year ends again with the
September equinox,
concluding another of billions of trips the Earth has taken
-- and will take -- around the Sun.
Explanation:
Venus now appears as planet Earth's brilliant
morning star
standing above the eastern horizon before dawn.
For most, the silvery celestial
beacon rose in a close pairing
with an old crescent Moon on February 26.
But seen from locations
in western Africa before sunrise,
the lunar crescent actually occulted or passed in front of Venus,
also in a crescent phase.
Farther to the east, the occultation occurred during daylight
hours.
In fact, this telescopic snapshot of the
dueling crescents was captured
just before the occultation began under an afternoon's
crystal clear skies from
Yunnan Province, China.
The unforgettable scene was easily visible to the naked eye
in broad daylight.
