Sky and Telescope - February 2016 - 41

OBSERVING

Northern Hemisphere's Sky

Fred Schaaf welcomes your
comments at fschaaf@aol.com.

Fred Schaaf

A Thousand Stars
Count the possibilities in the night skies of winter.

I like the mention of "the light of a thousand stars"
in the chorus of Ed Sheeran's hit song. Not fewer than
a thousand stars, so we know these young lovers are
blessed with a sky that's at least relatively free of light
pollution. But the song also doesn't engage in unknowledgeable hyperbole and claim a million stars.
The more I've thought about it, the more intriguing I've found the concept of a thousand stars. We can
explore the topic not just mentally indoors but also
visually outdoors - where the bright traditional constellations of winter oﬀer some wonderful opportunities to
see numerous stars, both with naked eye and optical aid.
Thinking about a thousand stars. How many
thousands of stars can be seen with the naked eye? The
answer depends ﬁrst on sky conditions - including light
pollution, of course - both near the zenith and at lower
altitudes in the sky, where more light is absorbed and
scattered. But there's another factor as well: the viewer's
observing skill. It takes practice to get better at using
"averted vision" (looking slightly away from a target object
so that its light falls on the outer parts of the retina where
there are greater numbers of light-sensitive rod cells).
I've always told people that more than just one or two
thousand stars can be seen under ideal conditions with
the naked eye. Perhaps the ancient Greeks used a special
word, "myriad" (meaning 10,000), because the most
prominent display of great number in nature was the
stars. They may have estimated that roughly "a myriad"
of stars could be seen in the sky.
But exalting in a sky of just a thousand stars has its
own merits. A "thousand" is a determinate number, and
it's within the reach of people with less-than-ideally dark
skies. The Millennium Star Atlas tells us there are 893
stars at magnitude 4.49 or brighter and 2,822 at 5.49 or
brighter. If the naked-eye limit is supposed to be 6.5, the
total grows to 8,768 naked-eye stars. But some observers
have seen stars as dim as magnitude 8.0 with the naked
eye, so we can imagine a number closer to a myriad.

A thousand winter stars. Snow cover can worsen
our faint limit by several magnitudes. Even the light
produced by a fairly dark night sky can make our limiting
magnitude markedly brighter. To see the faintest stars,
cup your hands around your eyes or block as much of the
sky from view as possible with trees or dark buildings.
On winter evenings, the region to keep in clear view is
the group of constellations centered on Orion. No one constellation has 1,000 naked-eye stars in it, but if you take the
stars brighter than 6.5 in the Orion group - Orion (204),
Taurus (223), Auriga (152), Gemini (119), Canis Minor (47),
and Canis Major (147) - and add them together, you get
892. Add the 73 stars of Lepus and you're closer to 1,000.
Add Monoceros (138) and you're over a thousand.
According to the Millennium Star Atlas, the richest
areas of the heavens (regions like Crux and Cygnus) can
display, in ideal conditions, more than 3,000 stars in a
typical ﬁeld of 7×50 binoculars. In winter, try the region
of Orion's Belt and Sword, or parts of Puppis, to see a
thousand stars in binoculars. With a telescope, you'll
need to check out one of winter's rich open clusters.
Even the Double Cluster in Perseus and M37 in Auriga
oﬀer mere hundreds of stars - but are still glorious. ✦

TIINA TÖRMÄNEN

Take me into your loving arms
Kiss me under the light of a thousand stars
Place your head on my beating heart
I'm thinking out loud
Maybe we found love right where we are.
- Ed Sheeran and Amy Wadge, Thinking Out Loud

Night Walk

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Sky and Telescope - February 2016

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