How small can the naked eye see?

Friday 9th April 2010
Submitted by Yan Wong
Fred Hollis, by email

Your naked eye can see objects of any size, if they emit or scatter enough light to trigger its detector cells. Light visible from the star Deneb covers a minuscule fraction of your visual field (its ‘angular diameter’ is 0.0024 arcseconds). A light-emitting object seen as the same size when 15cm from your face, would be 1.75 nanometres wide. That’s only about 10 times the width of an atom of gold! And you can ‘see’ smoke and fog, even when their constituent particles are too small to pick out.

What is limited is the eye’s resolution: how close two objects can become before they blur into one. At absolute best, humans can resolve two lines about 0.01 degrees apart: a 0.026mm gap, 15cm from your face. In practice, objects 0.04mm wide (the width of a fine human hair) are just distinguishable by good eyes, objects 0.02mm wide are not.

GOT A QUESTION?

Scratching your head over a burning scientific conundrum? Submit your question and we'll get our esteemed panel of experts to answer it for you.

 

Is there any science in astrology?
previous qanda Article
How does Osmosis Power work?
next qanda Article
Q&A Tabs

Viagra is the brand name for sildenafil citrate, a drug that was originally studied for use in patients with high blood pressure or heart disease. It works by blocking the action of an enzyme...

It’s not just humans that enjoy a smooch; lots of animals have courtship behaviours involving the mouth. Pigeons touch beaks, cats and dogs nuzzle each other, male fruit flies lick the...

Phlegm is the mucous secretion of the respiratory passages. The cilia cells that line these passages are continually driving the phlegm upward to the throat, where it triggers the swallow reflex...

Not for long. The gruesome idea of nails and hair continuing to grow on a rotting corpse is fascinating. But it’s a myth – at least if you’re thinking of luscious locks and long...

The powder is actually tiny scales made from modified hairs. Moths, like butterflies, belong to the order Lepidoptera, which means 'scale wing'. The scales are pigmented but they also contribute...

All female mammals have a clitoris, the sole purpose of which is to react to sexual stimulation, and presumably this stimulation has evolved to be pleasurable for most species. But establishing...

To create a sound, we have to set matter - whether it's a gas like air, a liquid or even a solid material - in regular motion, creating a wave of specific frequencies, which we hear as a sound of...

Mirrors don’t reverse left and right either – that’s just our interpretation of what happens. Your reflection in the mirror is actually reversed front to back – if you have...

Discovered by an American student named Gary Flandro in the mid-1960s, the slingshot manoeuvre usually involves spacecraft briefly 'coat-tailing' a planet orbiting the Sun, extracting some of the...

The ice disappears because the wind blows away water molecules that have evaporated or 'sublimed' from the ice, so the ice slowly shrinks in size. The molecules that escape are those with the...