Why aren't our eyes damaged from reflected sunlight while observing the moon ?

[StarFiveSky]

I know this is kind of a stupid question but I'm still curious.

We are always told, never to look or stare at the sun straight especially with observing equipment like binoculars or telescopes.

My question is, regarding those days when the moon reflects sunlight very well / those days when the moon is extremely bright, why is it fine to observe it with binoculars or telescopes and not get any eye damage ? 

 

I mean the moon is still reflecting sunlight into our eyes + equipment.

[Cornelius Varley]

4 minutes ago, StarFiveSky said:

I know this is kind of a stupid question but I'm still curious.

We are always told, never to look or stare at the sun straight especially with observing equipment like binoculars or telescopes.

My question is, regarding those days when the moon reflects sunlight very well / those days when the moon is extremely bright, why is it fine to observe it with binoculars or telescopes and not get any eye damage ? 

 

I mean the moon is still reflecting sunlight into our eyes + equipment.

The moon only reflects between 3 and 12% of the sunlight that hits it. Viewing the moon at or near it's fullest might be uncomfortable, but not dangerous. A suitable variable polarising filter or moon filter might help here.

[Davey-T]

I don't think the reflected sunlight is strong enough to damage eyesight it will however leave an impression upon the retina for a while.

Dave

[wulfrun]

There's nothing especially damaging about sunlight in particular*...except that when looking at the sun it's bright enough to cause damage. The moon is bright but is massively less bright than viewing direct sunlight.

EDIT * meaning it's not "special light"

Edited May 31, 2021 by wulfrun

[StarFiveSky]

Thanks for all the replies. @Cornelius Varley's numbers were a perfect explanation.

Question solved 

[Mr Spock]

The Moon is only illuminated the same way the Earth is. So it's only as bright as normal daytime.

The Moon only looks bright at night because it contrasts with the dark .

[Louis D]

The moon is about the same reflectivity as asphalt.  Do you ever get eye damage staring at asphalt at noon?

Here's an actual video of the moon transiting in front of the Earth.  It's not very bright compared to the earth, is it?

 

[Gfamily]

As Herschel discovered, as well as the visible light, sunlight contains significant amounts of Infra-Red light; and it's that, that causes the damage to the eye. 

The IR light is absorbed rather than reflected from the moon's surface, so doesn't make it back to us when we look at the moon.

 

[mikemarotta]

On 31/05/2021 at 13:27, Gfamily said:

As Herschel discovered, as well as the visible light, sunlight contains significant amounts of Infra-Red light; and it's that, that causes the damage to the eye. 

The IR light is absorbed rather than reflected from the moon's surface, so doesn't make it back to us when we look at the moon.

 

I agree about the Moon. However, I question the major premise. Regarding sunlight as experienced on Earth, the UV does the most damage to your eyes, not the IR.

Nature here:  https://www.nature.com/articles/eye2015266

US National Institutes of Health here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3872277/

 

[Gfamily]

10 hours ago, mikemarotta said:

I agree about the Moon. However, I question the major premise. Regarding sunlight as experienced on Earth, the UV does the most damage to your eyes, not the IR.

Nature here:  https://www.nature.com/articles/eye2015266

US National Institutes of Health here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3872277/

 

Those papers discuss long term cumulative damage to the lens and cornea, and it is true that UV does cause damage, but the question in this thread is about the dangers (or otherwise) of observing, where an image is formed at the retina.  Just like using a magnifying glass to start a fire, it's the IR light that causes the heating that causes the damage to the retina. 

 

 

Edited July 5, 2021 by Gfamily