Say Cheese!

June 20, 2013 5:55 PM

"It’s not inconceivable that if you are on the right part of the Earth, and you stand outside and wave, that one or two of the photons of sunlight that reflect from you are going to make it out to Saturn and into Cassini’s telescope." NASA is taking a new version of Carl Sagan's Pale Blue Dot image, and they've invited everyone to Wave at Saturn!
posted by brundlefly (22 comments total)

Something tells me they're also going to get photons from quite a few moons.
posted by benito.strauss at 6:07 PM on June 20, 2013 [8 favorites]

Not to be a party pooper, but it is pretty inconceivable that any human action would change the value recorded by any one pixel element of the Cassini image sensor. I don't think it's a single-photon camera (which do exist).
posted by CaseyB at 6:07 PM on June 20, 2013

And, benito, if you wanted to moon instead of wave, Cassini might catch a photon from Uranus.
posted by weapons-grade pandemonium at 6:08 PM on June 20, 2013 [7 favorites]

Something tells me they're also going to get photons from quite a few moons.

Those are no moons.
posted by DU at 6:32 PM on June 20, 2013 [1 favorite]

Inconceivable... you keep using that word. I do not think it means what you think it means.
posted by ElDiabloConQueso at 6:36 PM on June 20, 2013

Why not? I'm already winking at Neil Armstrong.
posted by arcticseal at 6:50 PM on June 20, 2013

This reminds me of a question I keep forgetting to submit XKCD's "What If...?" - assuming a stable wormhole that can transport us to any point in space, instantly, how large of a reflector (presumably measured in square light years) would we need to actually capture video of the death and non-resurrection of Christ?
posted by Ryvar at 6:51 PM on June 20, 2013 [2 favorites]

I have no idea what to wear.
posted by dragstroke at 6:53 PM on June 20, 2013 [4 favorites]

The ISS sensors are both CCDs.

If your hand is about 10 cm x 20 cm, and assuming its albedo is similar to the Earth's (30%, which is probably not a bad average), then just taking the ratio of the area of your palm to the projected area of the Earth, we find that your palm reflects 0.1*0.2/(4*pi*6,400,000²) *100 = 0.000000000000004% of the photons received by Cassini from Earth. (That's supposed to be 4x10^-15 percent, just in case I miscounted my zeros.)

ISS CCD pixels will be saturated after recording 120,000 photons [PDF]. The pixel receiving photons from Earth won't be anywhere near saturated, so the actual pixel count will be significantly smaller, but let's max out our chances by saturating the pixel. Let's also be optimistic and assume that the Narrow Angle Camera is used in 4x4 binning mode (combining 4x4 squares of pixel into one pixel), so that up to (but probably really much fewer than) 2 million photons are measured in each binned pixel.

So, using the most optimistic assumptions, the chances are one in 1/(2,000,000*0.00000000000000004) = 13,000,000,000 that one of your photons will be recorded. If, as is more likely, they use 1x1 binning (which is to say, no binning), the odds go down to 1 : 200,000,000,000. (And, since the pixels aren't really saturated, it's probably a factor of 100 or 1000 worse than that.)

So, yeah, the odds aren't great. Even if it isn't cloudy where you are.

(I am an astronomer who does photometry using Cassini data. I am not your astronomer. This is not astronomy advice.)
posted by BrashTech at 7:50 PM on June 20, 2013 [23 favorites]

I don't understand numbers much, but what I think BrashTech is saying is that I still have a chance.
posted by BozoBurgerBonanza at 7:58 PM on June 20, 2013 [11 favorites]

And yet if all 300-some million people in the U.S. went out and waved, there's about a two percent chance one of them would win. (I really hope that math is right, because I'm not double-checking it until the edit window closes.)
posted by introp at 8:07 PM on June 20, 2013

You absolutely have a nonzero chance.

We, as a species, and as an international community, built a robot and sent it to Saturn to take pictures for us.

Everyone who wants to take a shot should go out there and wave their darnedest.
posted by BrashTech at 8:13 PM on June 20, 2013 [10 favorites]

BrashTech is my new hero.
posted by matty at 8:44 PM on June 20, 2013

My question is when should you actually go outside and wave to have a chance of reflecting a photon into the sensor? The Facebook event page says this,

Cassini’s cameras will take a series of pictures over about 15 minutes in the afternoon of July 19 from 2:27 to 2:42 p.m. PDT (5:27 to 5:42 p.m. EDT; 21:27 to 21:42 UTC).

Given that Saturn will be 9.654 au from Earth on July 19th, and that's about 1.3369 light hours, should I actually go outside and wave at 4:07 p.m. EDT, or did they already take that into account in the posted times?
posted by ob1quixote at 9:28 PM on June 20, 2013 [4 favorites]

So, yeah, the odds aren't great. Even if it isn't cloudy where you are.

But somebody's gotta win. May as well be me! For once, lottery thinking has a legit purpose!
posted by DigDoug at 4:57 AM on June 21, 2013

To be safe, start waving now and don't stop until they say so.
posted by blue_beetle at 5:07 AM on June 21, 2013 [2 favorites]

BrashTech, is smart. We need him. He makes things go.
posted by cjorgensen at 6:16 AM on June 21, 2013 [2 favorites]

I don't understand numbers much, but what I think BrashTech is saying is that I still have a chance.

Various lottery organizations would also like you to know you also have a chance of winning millions of dollars this week and therefore you should give them some of your money. ;-)
posted by aught at 6:25 AM on June 21, 2013

Whoa, this is on what would've been my dad's 59th birthday. Guess I gotta do it. Though I already pretty much wave at space all the time. Hey, space!
posted by Eideteker at 6:27 AM on June 21, 2013

I just realized that they picked a time when Saturn is near superior conjunction (opposite the sun in the sky) so most of the light from Earth that reaches Saturn is not going to be reflected sunlight, as I assumed, but sunlight scattered through the Earth's atmosphere. This makes the calculation less straightforward, I'm afraid, but the good news is that your odds of influencing the light that reaches Cassini will go up, because the photons won't be coming from the whole disk of the planet, just the ring of atmosphere around the edge of Earth's disk. You will mainly be blocking the light, casting a shadow.

Given that Saturn will be 9.654 au from Earth on July 19th, and that's about 1.3369 light hours, should I actually go outside and wave at 4:07 p.m. EDT, or did they already take that into account in the posted times?

Since light-travel time is something you think about a lot in mission planning, and since Cassini lives on GMT (well, UT actually, but close enough) and they gave the time in PDT, I'm sure they took light-travel time into account.

But somebody's gotta win. May as well be me! For once, lottery thinking has a legit purpose!

Not to be a killjoy, but some photons from Earth are going to win. Not necessarily any photons that bounced off a person. But nonetheless, you can point to that image and say, every human being alive on July 19 from 2:27 to 2:42 p.m. PDT is right here on this blue dot, and I was there, too, looking up.

(He is a she, actually, cjorgensen. :) )
posted by BrashTech at 6:33 AM on June 21, 2013 [7 favorites]

It was pointed out to me on my question on the Facebook event page that the signal to activate the camera will be traveling towards the Cassini probe at the same speed as the photons from waved hands, viz. the speed of light. For whatever reason I presumed the mission would be pre-programmed into the probe to be executed at a certain time or at a certain position.
posted by ob1quixote at 12:34 AM on June 22, 2013

You're correct, ob1quixote, the spacecraft will have had commands uplinked well before the observation.
posted by BrashTech at 9:04 AM on June 22, 2013