- [Narrator] Whether it's to map the stars,
spy on other planets, or study the sun,
humans have been looking to the skies for millennia,
but some objects are safer to observe than others.
For example, astronomer Mark Thompson put a pig's eye
behind a regular telescope and aimed it at the sun,
and it burned a hole straight through the lenses
in about 20 seconds.
Now looking at the sun through a telescope
is an especially terrible idea,
but just how bad is it to glance up with the naked eye?
On a clear day the sun shines up to 5000 times brighter
than an average light bulb.
When something that bright strikes your eye,
a few things can happen.
If it's only for a moment the worst you'll experience
is a blurry splotch on your vision called an after image.
Normally light reaches the retina at the back of your eye
where it triggers photo receptors
that relay the information to your brain.
This is how you're able to see anything,
but bombard them with too much light at once,
and you can actually damage the cells and proteins
that help them process light.
Since your retina has no pain receptors
the damage won't hurt,
but it will leave the blurry splotch on your vision.
Usually it clears up in a few minutes
that is unless you keep staring.
Now you're doing more damage
than just overloading your retina.
For starters you're giving your eyes
an abnormally high dose of UV radiation,
the same stuff that causes sunburns.
Like your skin the cornea at the front of your eye
can also burn and that will hurt.
The cornea protects the rest of your eye,
and is therefore covered in pain receptors
that alert you whenever a pesky eyelash is on the loose,
but UV radiation isn't the only issue.
Too much visible light can penetrate your eye
and damage the retinal tissue
which causes a condition called solar retinitis.
This means parts of retina
can no longer process light normally,
so you can end up with entire chunks
of your vision blurred out.
Depending on the extent of the damage
recovery can take weeks, months,
and in severe cases over a year,
but in rare cases the damage is so extreme it never heals
leading to a rare condition called solar retinopathy.
This usually only shows up in reckless eclipse gazers.
Turns out during a solar eclipse most of the sun's light
is blocked which can actually trick your brain
into thinking it's safe to stare.
Normally our bodies have a built-in defense mechanism
against staring at the sun.
Specifically when we squint we look up
which minimizes the amount of light coming in
and protects our cornea and retina,
but during a solar eclipse the sun doesn't appear
bright enough to trigger our defense mechanisms,
so we can end up staring for longer than is safe.
Suffice to say there's nothing good
about staring at the sun,
so do your eyes a favor and avoid looking at it.
After all, there are around 6000 stars
in the night sky which you can safely observe
for as long you wish.