Stars Near and Far
The
December sky neatly frames the nearest and farthest stars visible to northern
viewers.
Deep-space distances
are so enormous that familiar measures are useless. That is why astronomers use
light-years, the distance that a beam of light (racing at 186,282.4 miles each
second) travels from one of your birthdays to the next. The best way to
link cosmic and human scales is to embrace the weirdness and think like a beam
of light — and this month is the perfect time to start.
The December sky neatly frames the
nearest bright star visible from northern locations (Sirius, 8.7 light years
away, rising in the southeast after sunset) and the most distant (Deneb,
roughly 2,500 light years away, setting in the northeast). The light from
Sirius you see tonight matches the age of a third grader, whereas Deneb’s light
set out when the Pharaohs were building pyramids in Egypt.
Capella, the yellow dazzler now nearly
overhead, is the star of middle age: 43 light years away. The stars of the Big
Dipper, low in the north, speak to the human lifespan. Many people on Earth
were alive 78 years ago when the light from Dubhe (the upper front star in the
dipper’s bowl) started its journey. None can match the age of the light from
Mizar (the middle star of the handle), 124 light-years away.
For the ultimate trip, look almost
straight up under dark skies for the faint, fuzzy oval of the Andromeda Galaxy.
The most distant object readily visible to the naked eye, it lies 2.54 million
light-years away. The bits of Andromeda’s light hitting your retina started
their journey when Homo habilis, the earliest member of our genus, first
scratched his brow in Africa’s Olduvai Gorge.
The
original link can be found at:
http://discovermagazine.com/2013/dec/23-urban-skygazer
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