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.