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On a clear night, away from city lights, the sky is full of stars, more than we could possibly
dream of counting, right?
Well, if there were a grain of sand for every star that we can see with the naked eye...
9,096. That’s it. Every star bright enough to be seen from Earth without the aid
of a telescope. Antares is one. Plus 1 to be exact, on the astronomical scale of brightness.
The sun checks in at minus 27. The full moon, minus 13.
Even in the darkest places on Earth, like Chile’s Atacama desert, our eyes can only
detect objects magnitude 6.5 or brighter.
But with bigger eyes? We can see a lot more.
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This is the Andromeda galaxy, the nearest major galaxy to the Milky Way. And it’s
full of stars.
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Earth is surrounded by 360 degrees of space in every direction. Take an arc of one degree,
divide it into sixty, and that’s an arcminute.
This 1.5 billion pixel image from the Hubble telescope covers about a thousand square arcminutes,
and contains more than 100 million stars.
Let’s put that in perspective. If it was brighter, this is what Andromeda
would look like next to our moon.
But we don’t have to look at an area of sky that big to find 100 million stars.
Let’s take a closer look at this little piece of sky.
The Hubble telescope was aimed at this sliver of sky, its shutter opened for 2 million seconds,
and from a seemingly empty corner of space emerged not stars, but thousands of galaxies.
Some of these are as old 13.2 billion years, photons emitted near the beginning of the
universe itself. The faintest objects in this image are ten billion times dimmer than we
can see with our own eyes.
It would take 30 million squares the size of the Hubble Extreme Deep Field to cover
the entire sky.
Scientists estimate that the observable universe contains about 200 billion galaxies. If, instead
of stars, we made every grain of sand a galaxy, it would fill 27 cubic meters.
So how many stars are there? Maybe 1 septillion, That’s a number that’s so big, that
it doesn’t make sense. But one thing we can be sure of, there’s not enough beaches
on Earth to hold them all.
Carl Sagan said that “Earth is the shore of the cosmic ocean”… so remember, each
night when we look up at a sky seemingly filled with stars, we’re only dragging a finger
through the sand.
Stay curious