How small are we in the scale of the universe? - Alex Hofeldt

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In 1995, scientists pointed the Hubble Telescope at an area of the sky near the Big Dipper. The location was apparently empty, and the whole endeavor was risky – what, if anything, was going to show up? But what came back was nothing short of spectacular: an image of over 1,500 galaxies glimmering in a tiny sliver of the universe. Alex Hofeldt helps us understand the scale of this image.

Lesson by Alex Hofeldt, animation by Bliink.

Hubble Deep Field Image Credit: R. Williams (STScI), the Hubble Deep Field Team, and NASA.

In the winter of 1995,

scientists pointed the Hubble Telescope
at an area of the sky near the Big Dipper,

a spot that was dark and out of the way
of light pollution from surrounding stars.

The location was apparently empty,
and the whole endeavor was risky.

What, if anything, was going to show up?

Over ten consecutive days,

the telescope took close to 150 hours
of exposure of that same area.

And what came back
was nothing short of spectacular:

an image of over 1,500 distinct galaxies

glimmering in a tiny sliver
of the universe.

Now, let's take a step back to understand
the scale of this image.

If you were to take a ballpoint pen

and hold it at arm's length
in front of the night sky,

focusing on its very tip,

that is what the Hubble Telescope captured
in its first Deep Field image.

In other words,

those 3,000 galaxies were seen
in just a tiny speck of the universe,

approximately one two-millionth
of the night sky.

To put all this in perspective,

the average human measures
about 1.7 meters.

With Earth's diameter
at 12,700 kilometers,

that's nearly 7.5 million humans
lined up head to toe.

The Apollo 8 astronauts flew a distance
of 380,000 kilometers to the moon.

And our relatively small Sun has a
diameter of about 1.4 million kilometers,

or 110 times the Earth's diameter.

A step further,

the Milky Way holds somewhere
between 100 to 400 billion stars,

including our Sun.

And each glowing dot of a galaxy captured
in the Deep Field image

contains billions of stars
at the very least.

Almost a decade after taking
the Deep Field image,

scientists adjusted the optics
on the Hubble Telescope

and took another long exposure
over a period of about four months.

This time, they observed 10,000 galaxies.

Half of these galaxies have since been
analyzed more clearly

in what's known as
the eXtreme Deep Field image,

or XDF.

By combining over ten years
of photographs,

the XDF shows galaxies so distant

that they're only
one ten-billionth the brightness

that the human eye can perceive.

So, what can we learn about the universe
from the Deep Field images?

In a study of the universe, space and time
are inextricably linked.

That's because of
the finite speed of light.

So the Deep Field images are like
time machines to the ancient universe.

They reach so far into space and time

that we can observe galaxies
that existed over 13 billion years ago.

This means we're looking
at the universe as it was

less than a billion years
after the Big Bang,

and it allows scientists to research
galaxies in their infancy.

The Deep Field images have also shown
that the universe is homogeneous.

That is, images taken at different
spots in the sky look similar.

That's incredible when we think about
how vast the universe is.

Why would we expect it to be the same
across such huge distances?

On the scale of a galaxy,
let alone the universe,

we're smaller than
we can readily comprehend,

but we do have the capacity to wonder,

to question,

to explore,

to investigate,

and to imagine.

So the next time you stand gazing up
at the night sky,

take a moment to think about the enormity
of what is beyond your vision,

out in the dark spaces between the stars.