Picture of Earth from Jupier/Saturn

Hi
Just curious. I know the Voyager turned back and took a picture of our solar
system with some planets. That was quite a poor quality one. Recently, they
took one image of earth from mars which looked interesting.A nice blue
crescent. I wonder if I was on mars and has an LX200 10" or Nexstar 9.25,
would the view of earth be breathtaking? I also wonder if the probe around
Saturn ever turned back to take a picture of earth...
anyone knows?
thanks in advance

--
Please delete "-abc" from e-mail address when replying. Thanks

In article , Rskt wrote:
I also wonder if the probe around
Saturn ever turned back to take a picture of earth.

I don't recall hearing of any such, and considering that the camera are all
oriented in a direction perpendicular to the axis of the radio antennae, I would
doubt it was done - to point a camera at the Earth, the spacecraft would have to
be turned so that the antennae did not point towards Earth. Which would break the
radio connection. There are sub-systems for keeping the spacecraft's orientation
without direct control from the Earth, and for regaining orientation if some
unexpected event disturbed orientation. But the risk of triggering a malfunction
by trying to point the spacecraft off it's intended line probably wouldn't be
worth the result.
During the Earth fly-by (18th Aug 1999) ...
Nine of Cassini's 12 science instruments were turned on to make observations
of the Earth/Moon system. Scientific and engineering data from the Earth
flyby will be transmitted by Cassini to receiving stations of NASA's Deep
Space Network over coming days.

(From http://saturn.jpl.nasa.gov/news/pres...90817-pr-a.cfm , the
NASA press release.)
http://saturn.jpl.nasa.gov/news/pres...01230-sn-a.cfm has information
about the data acquired during the Jupiter fly-by.

http://ciclops.lpl.arizona.edu/view.php?id=77 has information from the imaging team
about photography of the Moon during the Earth fly-by.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

In message , RSKT
writes
Hi
Just curious. I know the Voyager turned back and took a picture of our solar
system with some planets. That was quite a poor quality one. Recently, they
took one image of earth from mars which looked interesting.A nice blue
crescent. I wonder if I was on mars and has an LX200 10" or Nexstar 9.25,
would the view of earth be breathtaking? I also wonder if the probe around
Saturn ever turned back to take a picture of earth...
anyone knows?
thanks in advance


I think Cassini took some pictures of Earth during its fly-by, but
there's one from Galileo which you can find at
http://jura.astro.utoledo.edu/~karen...res/solarsys/g
alileo_earthmoon.htm and probably elsewhere. And while the Japanese
Nozomi failed at Mars it produced a beautiful Earth-Moon picture which
was Astronomy Picture of the Day September 4, 1998
http://antwrp.gsfc.nasa.gov/apod/ap980904.html.

Aidan Karley wrote:

In article , Rskt wrote:
I also wonder if the probe around
Saturn ever turned back to take a picture of earth.

I don't recall hearing of any such, and considering that the camera are all
oriented in a direction perpendicular to the axis of the radio antennae, I would
doubt it was done - to point a camera at the Earth, the spacecraft would have to
be turned so that the antennae did not point towards Earth. Which would break the
radio connection. There are sub-systems for keeping the spacecraft's orientation
without direct control from the Earth, and for regaining orientation if some
unexpected event disturbed orientation. But the risk of triggering a malfunction
by trying to point the spacecraft off it's intended line probably wouldn't be
worth the result.

Aidan, you're right about the orientation of the camera. However,
Cassini spends about 15 hours a day with its high-gain antenna NOT
pointed
at Earth. The other 9 hours are devoted to sending back the data from
the previous 15.

The real reason Cassini won't take any pictures of Earth is that it's
too close to the Sun -- maximum elongation is only about 6 degrees --
and there are instrument health and safety flight rules that prohibit
aiming the cameras that close to the Sun. The exception is when we're
in Saturn's shadow, but then there's high-priority science to be done.

A picture of Earth rising over a thin crescent Saturn sounds pretty,
but Earth would be only 1.5 pixels across in the narrow-angle camera.
It would be another "pale blue dot" kind of image.

-- Bill Owen, Cassini navigation team

In article , Bill Owen wrote:
The real reason Cassini won't take any pictures of Earth is that it's
too close to the Sun -- maximum elongation is only about 6 degrees --
and there are instrument health and safety flight rules that prohibit

A la Hubble. I should have thought of that.

However,
Cassini spends about 15 hours a day with its high-gain antenna NOT
pointed
at Earth. The other 9 hours are devoted to sending back the data from
the previous 15.

So, this gives you more freedom in the orientation of the
instruments. But also does away with the need for a steerable antenna if
you needed to orientate on both a target and on the Earth. Timeshift the
issues and make sure the recorder is as empty as possible before each
fly-by. I had a nagging feeling that I was missing something when I
posted my original response.

People must have sweated some pretty heavy blood when the tape
recorder on Galilelo started go wonky. Touch wood the solid state memory
in Cassini will have fewer issues. There must be some heavy-duty code to
do error corrections though.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

In message d, Aidan
Karley writes
In article , Rskt wrote:
I also wonder if the probe around
Saturn ever turned back to take a picture of earth.

I don't recall hearing of any such, and considering that the
camera are all
oriented in a direction perpendicular to the axis of the radio
antennae, I would
doubt it was done - to point a camera at the Earth, the spacecraft
would have to
be turned so that the antennae did not point towards Earth. Which would
break the
radio connection. There are sub-systems for keeping the spacecraft's
orientation
without direct control from the Earth, and for regaining orientation if some
unexpected event disturbed orientation. But the risk of triggering a
malfunction
by trying to point the spacecraft off it's intended line probably wouldn't be
worth the result.
During the Earth fly-by (18th Aug 1999) ...
Nine of Cassini's 12 science instruments were turned on to make observations
of the Earth/Moon system. Scientific and engineering data from the Earth
flyby will be transmitted by Cassini to receiving stations of NASA's Deep
Space Network over coming days.

(From http://saturn.jpl.nasa.gov/news/pres...90817-pr-a.cfm , the
NASA press release.)
http://saturn.jpl.nasa.gov/news/pres...01230-sn-a.cfm has
information
about the data acquired during the Jupiter fly-by.

http://ciclops.lpl.arizona.edu/view.php?id=77 has information from the
imaging team
about photography of the Moon during the Earth fly-by.

According to http://pages.preferred.com/~tedstryk/mooncass.html the
reason Cassini didn't take many images during its fly-by was budget
constraints!
If true, that's absurd - you've already spent over a billion dollars;
doesn't it make sense to spend some money to get some positive PR and
more calibration images? I wonder if it had something to do with not
reminding the kooks and protesters that a nuclear-powered spacecraft was
approaching Earth.
--
What have they got to hide? Release the ESA Beagle 2 report.
Remove spam and invalid from address to reply.

In article , Jonathan Silverlight
wrote:
According to http://pages.preferred.com/~tedstryk/mooncass.html the
reason Cassini didn't take many images during its fly-by was budget
constraints!
If true, that's absurd

IF true, that is absurd. IF it's true. However, since the records
on the JPL site indicate that 9 of the 12 instruments on Cassini were
powered up, then they'd have needed a pretty full complement in the
control room and about the only on-going cost related to the quantity of
imaging would have been the time on DSN to downlink the imaging.
Trivial.
Various other mentions on the engineering aspects of Cassini
indicate that there were substantial thermal constraints on Cassini
during it's inner-system manoeuvers. The RTGs are churning out heat all
the time, and heat is coming into the machine from solar irradiation.
During a lot of the flight the radio antennae were used to act as a
sunshield, since solar irradiation at Earth-range would be approximately
90 times more intense at Earth-orbit than at Saturn orbit.
Stryk also mentions (in the case of a Galileo fly-by of Almathea)
the risk of putting the spacecraft into shut-down by trying to do too
much in a fly-by. Combining those data I'd put Stryk's "budgetary
constraints" comment into the "unsupported assertion" category. There
are quite sufficient engineering grounds, IMHO, for only using some of
the instruments during the fly-by.

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

On Wed, 15 Sep 2004 00:50:12 +0800, "RSKT"
wrote:

Hi
Just curious. I know the Voyager turned back and took a picture of our solar
system with some planets. That was quite a poor quality one. Recently, they
took one image of earth from mars which looked interesting.A nice blue
crescent. I wonder if I was on mars and has an LX200 10" or Nexstar 9.25,
would the view of earth be breathtaking?

Leaving aside for the moment that on Mars, you probably wouldn't have
any breath to take, the view should be pretty impressive when the
Earth is near its greatest elongation. It would be smaller and not as
bright as Venus seen from here, but with lots more detail to see.

Al Moore

"RSKT" wrote in message ...
Hi
Just curious. I know the Voyager turned back and took a picture of our solar
system with some planets. That was quite a poor quality one. Recently, they
took one image of earth from mars which looked interesting.A nice blue
crescent. I wonder if I was on mars and has an LX200 10" or Nexstar 9.25,
would the view of earth be breathtaking? I also wonder if the probe around
Saturn ever turned back to take a picture of earth...
anyone knows?
thanks in advance

Earth from Mars would be fairly interesting. For one thing, the Moon
is visible from Mars without a telescope (so the "twin planet" evening
star would be pretty to anyone strolling around during early Martian
evening -- a brilliant blue planet and a faint white companion), and
through a decent small telescope one would see the Moon and Earth
showing matching phases (just as Venus does to us).

However, Earth would be fairly small in a Martian scope. The only time
it'd be close enough to show any significant surface features, it'd be
a thin crescent. (During Earth-Mars opposition, when we on Earth
train telescopes on Mars because it's the only time we can see it at a
decent apparent size, Earth would be in line with the Sun from Mars'
point of view, and furthermore would have its night side turned toward
Mars.)

From Saturn you'd see nothing of interest. Apart from the miniscule
separation between Earth and the Sun, Earth is just too small.
Consider: Earth is a little more than twice the diameter of Ganymede,
and Saturn is just about twice the distance from Earth as Jupiter.
Earth would appear as large, to a telescope on (let us say) Iapetus,
as Ganymede appears to a telescope on Earth.

In my 11" Celestron at highest magnification, I can barely tell
Ganymede is a disc rather than a point. I doubt Cassini has a much
better scope than mine. Cassini is too far away to see Earth.

eyelessgame