

Cassini to image the Earth tonight  - rowanseymour
http://saturn.jpl.nasa.gov/news/waveatsaturn/timezones/

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WestCoastJustin
_At Saturn 's enormous distance, the crescent Earth, with most of North
America illuminated by the sun, will span a single pixel and will appear as a
pinpoint of light in the depths of space [1, 2]._ FYI - The Cassini cameras
are 1-megapixel cameras, modes include 1024x1024, 512x512, and 256x256 pixels
[3].

I work at an observatory and there was some internal discussion this morning
about heading outside to wave. Cool idea, but I don't think you are going to
be able to see yourself in the image ;)

Times for anyone in the US to head outside:

    
    
      U.S. - Hawaii-Aleutian Stand. Time  Fri 11:27 AM 	11:27 	HAST
      United States - Alaska Daylight     Fri 1:27 PM 	13:27   (24/h) 	AKDT
      U.S. - Pacific Daylight Time 	      Fri 2:27 PM 	14:27 	PDT
      U.S. - Mountain Daylight Time       Fri 3:27 PM 	15:27 	MDT
      U.S. - Central Daylight Time 	      Fri 4:27 PM 	16:27 	CDT
      U.S. - Eastern Daylight Time 	      Fri 5:27 PM 	17:27 	EDT
    

[1] [http://www.cbsnews.com/8301-205_162-57594419/cassini-
spacecr...](http://www.cbsnews.com/8301-205_162-57594419/cassini-spacecraft-
set-to-capture-pale-blue-dot-of-earth/)

[2] [http://blogs.scientificamerican.com/life-
unbounded/2013/06/1...](http://blogs.scientificamerican.com/life-
unbounded/2013/06/19/return-to-the-pale-blue-dot/)

[3]
[http://saturn.jpl.nasa.gov/faq/FAQRawImages/#q5](http://saturn.jpl.nasa.gov/faq/FAQRawImages/#q5)

~~~
Osmium
So I've seen some gorgeous images from Cassini, but I could've sworn they're
all much higher than 1 megapixel. Do you have any info for how that works?

~~~
WestCoastJustin
I would checkout the FAQ page @
[http://saturn.jpl.nasa.gov/faq/](http://saturn.jpl.nasa.gov/faq/)

I am not sure how the Cassini imagery works, but for something like Hubble
Space Telescope (HST), here is what a raw image [1] looks like of M51 [2].
Typically the images you see from HST of M51 [3] will be a compilation of
dozens of raw images using colour filters.

[1] [http://i.imgur.com/qtQdcBS.jpg](http://i.imgur.com/qtQdcBS.jpg)

[2]
[https://en.wikipedia.org/wiki/Whirlpool_Galaxy](https://en.wikipedia.org/wiki/Whirlpool_Galaxy)

[3]
[https://en.wikipedia.org/wiki/File:Messier51_sRGB.jpg](https://en.wikipedia.org/wiki/File:Messier51_sRGB.jpg)

~~~
Osmium
Thanks :) The links are much appreciated! I have to say, purely from an
artistic point of view, there's something a lot more dramatic about the raw
images than the final one (at least to my eyes). I think it's a combination of
the contrast, and the fact that the object is too big to fit in the frame that
gives it a sense of scale.

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cdevroe
I will be waving. Cuz I'm a dork. But I will actually be waving.

Come to think of it. I might even throw a waving party of some sort. Hold up a
sign, have some beer, play some The Blue Danube via Spotify over Airplay.

~~~
fnordfnordfnord
Shine a spotlight in the direction of Saturn, or build a fire. I wonder how
much light you'd need to emit to have a noticeable effect? The Narrow Angle
Camera is 1024x1024 I think[1], I have no idea what integration time, so my
first guess is that we need to get a major city to riot/burn, or start a
forest fire. Hmm, on second thought, maybe I'd better just have a beer and
wave like cdevroe.

[1] Based on the properties of this image
[http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS...](http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS70/N00175897.jpg)

~~~
duskwuff
Not quite the same question, but related - XKCD did a "What If" on whether, if
everyone on Earth shone a laser at the Moon, it'd be visible. (TL;DR: No.)

[http://what-if.xkcd.com/13/](http://what-if.xkcd.com/13/)

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arrrg
In 2006 Cassini already took a beautiful image of Saturn with the Earth
visible:
[http://apod.nasa.gov/apod/ap061016.html](http://apod.nasa.gov/apod/ap061016.html)

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nhoss2
I love the romance of this. Even though the earth is only going to be a few
pixels, the frame will contain a snapshot of the entire human race.

~~~
TravisLS
That's one of my favorite things about the famous Earthrise photo:
[http://en.wikipedia.org/wiki/Earthrise](http://en.wikipedia.org/wiki/Earthrise)

The frame contains every living human, and every human who has ever lived -
except for three of them.

~~~
sadkingbilly
> every human who has ever lived

How is that, exactly? Doesn't the picture only contain the light captured at
that moment?

~~~
T-hawk
"The frame contains". Meaning that every dead and then-living human was within
the camera's view frustum, except for the three in the spacecraft. Not
considering whether they're in the nighttime part of the planet or on the far
side away from the camera; just that they're somewhere within the field of
view.

Presumably many photos of the Earth from spacecraft have achieved the first
part of that criterion, as Cassini's will. But the set of photos of most of
the human race minus a few is much smaller: limited to the moon missions,
because the shuttle and space station orbit too low to fit the entire Earth in
one camera frame.

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biot
Assuming perfect accuracy, how many people would it take aiming standard laser
pointers at Cassini during the imaging to noticeably impact the resulting
image?

~~~
wikwocket
Based on XKCD's research ([http://what-if.xkcd.com/13/](http://what-
if.xkcd.com/13/)), I am guessing the short version of the answer is, "More
than we have."

~~~
biot
That's hilarious. However, my question involves impacting the optical imaging
system of Cassini which is many, many orders of magnitude easier than
overcoming direct illumination from the Sun. The real issue is the matter of
beam dispersion rather than having insufficient power, as an astronaut 10
meters away could easily blind Cassini's optical imaging system using a laser
pointer.

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nsxwolf
I'll wave when they send a bigger camera.

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thehme
I will be waving from WTC (NYC), so hopefully other people will too.
5:27-5:42PM ET. Space programs are awesome!

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Achshar
A bummer, saturn is currently visible here, but will be on the other side of
the planet when the time comes.

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StavrosK
Isn't Cassini near Saturn? How is it going to image the Earth? Why are we
waving?

~~~
JonnieCache
_> How is it going to image the Earth?_

The sun is being blocked by saturn itself, so the earth will be visible to the
camera. The real purpose is to image the rings. Actual info is here:
[http://saturn.jpl.nasa.gov/news/waveatsaturn/](http://saturn.jpl.nasa.gov/news/waveatsaturn/)

 _> Why are we waving?_

To ensure NASA's continued funding/for a bit of innocent amusement. Take your
pick.

~~~
StavrosK
Right, so it's going to be far from the street-level imaging Google does, as I
suspected.

~~~
dysfunction
Earth will be a few pixels at best. The pale blue dot photo has basically a
single pixel of Earth, though Voyager was farther away than Cassini at the
time (past the orbit of Saturn) and its cameras weren't as good.

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tehwalrus
which way is saturn at the moment? if it's only imaging for 15 mins, it surely
can't see all of us!

~~~
jsmcgd
I just tried to work that out using a basic app on my phone. My 'calculations'
say that Saturn will be to the north east of the moon if you're in the UK? I
spent about 3 seconds on this. Can anyone confirm/correct this?

Edit: by north east I mean if you imagine that the moon is on the centre of
the map and you look up and to the right from it.

Edit 2: Looks like Saturn will be in the bottom of the constellation Virgo.

~~~
tehwalrus
ah, so I will be in the field of view, if still too small for the horizontal
resolution? cool! thanks :)

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lee4han
Say 'Cheese', guys!

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joeyrobert
Everyone SMILE! Say cheese!

