‘Pillock’ chastised for trying to paint dark side of moon red

Scientists come out in force

  • alert
  • submit to reddit

Choosing a cloud hosting partner with confidence

Millions wanted to paint dark side of moon red

Tim Richardson's story about one man's stunt aimed at colouring the moon red by using laser pointers caused a few raised eyebrows among the more scientific members of our readership.

Could this moon-decorating stunt work? Here's Domonic Fulford's thoughts on the matter:

This man is clearly a pillock.


minmum distance to moon = 350000km
angular dispersion of HeNe laser ~ .01 degrees (conservative)
power of pen laser << 1 Watt very conservative

we have

350,000 * tan (.01) = radius of spot on moon

This works out at 3500 km

if six billion people with very powerful laser pointers shone them at the moon that would be 6 billion watts over an area of 12 million sq km (3500 square (forget the pi)

or about 500 watts per square kilometer. Or .0005 Watts/sqm ! Sounds pretty damn bright to me.


Meanwhile, many thanks to Matthew Leigh, who provided the following analysis.

Hi, felt I had to share my opinion on the artist who plans to paint the moon red...

A few calculations, based on some simple optics theory. All assumptions are weighted such that reality will cause a worse outcome (in other words, this is a best case analysis).

Assume that the laser pointers have 1 degree of divergence (real pointers can have up to 30 degrees). Shining a point source with 1 degree of divergence from the earth to the moon (380,000 km on average) gives a spot radius of 6,600 km, which gives a spot area of 138,216,000,000,000 m^2. It will actually be more than this because laser beams diffract with a Gaussian envelope, not a linear envelope.

Now the key factor for visiblity is intensity, which is optical power divided by spot size. A typical laser pointer has 1mW of power - we'll assume 1W, and also assume no attenuation throughout the atmosphere. That gives 7*10^-15 W/m^2 of intensity per person on the moon's surface. Then, if you assume that the moon's surface is perfectly reflecting and that the
spreading factor is the same on the way back, we have 10^-30 W/m^2 of intensity hitting the observer on the ground, per person.

Everyone still following this?

I'm not 100% sure what the minimum intensity visible by the human eye is, but if every person on earth shone a laser pointer at the moon, the reflected intensity would be in the order of 10^-21 W/m^2, and that is definitly not visible. In other words, the guy is dreaming.

You probably stopped reading a long time before, but there has been a laser beam bounced off the moon before. It didn't cause a reddish hue, but it was detected by a very sensitive photodetector. The Apollo astronauts left a total internal reflector on the surface of the moon, and some physicists focused a laser through an enormous telescope, the sort used for looking at distant galaxies. Even then it was incredibly difficult to detect the received photons.

Remote control for virtualized desktops

More from The Register

next story
MEN: For pity's sake SLEEP with LOTS of WOMEN - and avoid Prostate Cancer
And, um, don't sleep with other men. If that's what worries you
Jim Beam me up, Scotty! WHISKY from SPAAACE returns to Earth
They're insured for $1m, before you thirsty folks make plans
Now: The REAL APPLE NEWS you need to know
OMG! Gravity's totes amazeballs. Calm down, George Clooney, not your film
Boffins who stare at goats: I do believe they’re SHRINKING
Alpine chamois being squashed by global warming
Let's make an app that POSTS your POO to APPLE HQ
Plus: It's OPEN WARFARE in the Linux greybeard world
Adorkable overshare of words like photobomb in this year's dictionaries
And hipsters are finally defined as self-loathing. Sort of
Not a loyal follower of @BritishMonarchy? You missed The QUEEN*'s first Tweet
Her Maj opens 'Information Age' at the Science Museum
Apple CEO Tim Cook: My well-known gayness is 'a gift from GOD'
'I have benefited from the sacrifice of others'
prev story


Cloud and hybrid-cloud data protection for VMware
Learn how quick and easy it is to configure backups and perform restores for VMware environments.
Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Saudi Petroleum chooses Tegile storage solution
A storage solution that addresses company growth and performance for business-critical applications of caseware archive and search along with other key operational systems.
The hidden costs of self-signed SSL certificates
Exploring the true TCO for self-signed SSL certificates, including a side-by-side comparison of a self-signed architecture versus working with a third-party SSL vendor.