Opportunity knocks when you're already in the Spirit...

OK, cheesy subject line. But what I'm curious about--the date is fast
approaching when it is likely that we will have TWO functioning rovers
on Mars, but unlike for Viking, they'll be moving around -- which
leads to the problem of understanding where they are.

I've heard that there's already a somewhat standard coordinate system
for Mars (I mean an established Prime Meridian), but I haven't seen
any NASA press releases referring to the current LAT/LONG of Spirit.
Anybody know where it is?

Which brings me to another question-- who picked the Prime Meridian
for Mars and what is it based on? It better be good. (At least that
English dude picked his hometown, right?)



Tom Merkle

Tom Merkle wrote:
I've heard that there's already a somewhat standard coordinate system
for Mars (I mean an established Prime Meridian), but I haven't seen
any NASA press releases referring to the current LAT/LONG of Spirit.
Anybody know where it is?

To my best knowledge, Spirit is in Gusev Crater, 14.6 South and 184.7 West.
See for example:
http://www.giss.nasa.gov/tools/mars24/help/guide.html
However, this map shows some difference:
http://marsoweb.nas.nasa.gov/landing...s/final/Gusev/

Which brings me to another question-- who picked the Prime Meridian
for Mars and what is it based on? It better be good. (At least that
English dude picked his hometown, right?)

Mars has "areographic coordinate system" (Earth has geographic, Sun has
heliographic, Moon has selenographic etc. General term is "planetographic".).
Prime meridian passes through crater names "Airy-O" in Mars.
See other meridians in different planets:
http://history.nasa.gov/SP-467/ch6.htm


Matti Anttila
--
http://masa.net/

In article , Tom Merkle wrote:
OK, cheesy subject line. But what I'm curious about--the date is fast
approaching when it is likely that we will have TWO functioning rovers
on Mars, but unlike for Viking, they'll be moving around -- which
leads to the problem of understanding where they are.

I've heard that there's already a somewhat standard coordinate system
for Mars (I mean an established Prime Meridian), but I haven't seen
any NASA press releases referring to the current LAT/LONG of Spirit.
Anybody know where it is?

Which brings me to another question-- who picked the Prime Meridian
for Mars and what is it based on? It better be good. (At least that
English dude picked his hometown, right?)

Greenwich runs through, IIRC, the site of the Royal Observatory, which
makes pretty good sense g

The IAU finally decided, in 1972, that the prime meridian ran through
the geometric centre of a small crater, inside a larger crater - itself
named for Airy, who originally calibrated the Greenwich meridian...

http://spaceflightnow.com/news/n0102/17mgsairy0/

--
-Andrew Gray

In article ,
Andrew Gray wrote:
Greenwich runs through, IIRC, the site of the Royal Observatory, which
makes pretty good sense g

If you're British, that is. :-) The French and the Germans, to name just
two, had different opinions on the matter -- you can find old maps which
put zero longitude on Paris or Berlin instead. Only quite late in the
19th century was there grudging agreement to do things Britain's way.

On planets like Mars, with no special reason to pick one place or another,
mapmakers have, similarly, made essentially arbitrary choices. (On some
other bodies there *are* reasons to prefer specific locations. For
example, on the Moon the zero meridian is approximately at the center of
the nearside.)

The IAU finally decided, in 1972, that the prime meridian ran through
the geometric centre of a small crater, inside a larger crater - itself
named for Airy, who originally calibrated the Greenwich meridian...
http://spaceflightnow.com/news/n0102/17mgsairy0/

Small correction: the IAU *ratified* a decision made by mapmaker Merton
Davies, which in turn refined a decision by mapmaker G.V. Schiaparelli.
(What the IAU did do, I think, was choose the name for the crater.)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article , Henry Spencer wrote:
In article ,
Andrew Gray wrote:
Greenwich runs through, IIRC, the site of the Royal Observatory, which
makes pretty good sense g

If you're British, that is. :-)

Wait, you don't all recognise that South London is the centre of the
universe?

I meant that it was a little more logical than through someone's home
town - it was a well-surveyed point, one a good amount of work was done
at, and whilst the decision to run through there may have been
arbitrary, the choice of that specific point wasn't.

The French and the Germans, to name just
two, had different opinions on the matter -- you can find old maps which
put zero longitude on Paris or Berlin instead.

I am reminded of the story about the German scientist told that Daguerre
had developed photography - his response was that it was inconcievable!
God would never allow such a thing to happen - and if he did, well, a
German would obviously have discovered it...

Only quite late in the
19th century was there grudging agreement to do things Britain's way.

On planets like Mars, with no special reason to pick one place or another,
mapmakers have, similarly, made essentially arbitrary choices. (On some
other bodies there *are* reasons to prefer specific locations. For
example, on the Moon the zero meridian is approximately at the center of
the nearside.)

I hauled out a map to check this, and see if there was anything
interesting there - there isn't, but two Surveyor missions were targeted
at Sinus Medii. Was there any particular reason for that other than
geologically?

(The meridian does seem to run through the centre of a small crater by
the Alps, but that's a not improbable coincidence.)

The IAU finally decided, in 1972, that the prime meridian ran through
the geometric centre of a small crater, inside a larger crater - itself
named for Airy, who originally calibrated the Greenwich meridian...
http://spaceflightnow.com/news/n0102/17mgsairy0/

Small correction: the IAU *ratified* a decision made by mapmaker Merton
Davies, which in turn refined a decision by mapmaker G.V. Schiaparelli.
(What the IAU did do, I think, was choose the name for the crater.)

Was Schiaparelli using the same rough location as Madler/Beer? I get the
impression he was, but the book I have here's quite vague...

--
-Andrew Gray

In article ,
Andrew Gray wrote:
example, on the Moon the zero meridian is approximately at the center of
the nearside.)

I hauled out a map to check this, and see if there was anything
interesting there - there isn't, but two Surveyor missions were targeted
at Sinus Medii. Was there any particular reason for that other than
geologically?

Three Surveyors, actually. Surveyor 2 was targeted there, but tumbled out
of control and crashed after one vernier engine failed to fire. 3 was
already committed elsewhere, but 4 made another try, and suddenly went
silent a couple of minutes before landing. (Probably its solid retro
exploded, but nobody is sure. Just possibly it made a safe landing after
a radio failure.) 6 finally succeeded.

The main reason for wanting to go there, actually, was support for Apollo:
Sinus Medii was considered a prime Apollo landing site at the time. The
geologists didn't really have a serious voice in target selection until
Surveyor 7.

Small correction: the IAU *ratified* a decision made by mapmaker Merton
Davies, which in turn refined a decision by mapmaker G.V. Schiaparelli.
(What the IAU did do, I think, was choose the name for the crater.)

Was Schiaparelli using the same rough location as Madler/Beer? I get the
impression he was, but the book I have here's quite vague...

The impression I have is that M/B didn't actually impose a coordinate
system on Mars, and Schiaparelli, being the first to do that, got to pick
its origin. But the information I have isn't definitive either.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article , Matti Anttila
wrote:

Tom Merkle wrote:
I've heard that there's already a somewhat standard coordinate system
for Mars (I mean an established Prime Meridian), but I haven't seen
any NASA press releases referring to the current LAT/LONG of Spirit.
Anybody know where it is?

To my best knowledge, Spirit is in Gusev Crater, 14.6 South and 184.7 West.
See for example:
http://www.giss.nasa.gov/tools/mars24/help/guide.html
However, this map shows some difference:
http://marsoweb.nas.nasa.gov/landing...s/final/Gusev/

Apparently there are plans to use radio location & the orbiters to
obtain a more precise fix on the MER landers. See:

http://www.msss.com/mer_mission/finding_mer/

--
Stephen Souter

http://www.edfac.usyd.edu.au/staff/souters/

"Matti Anttila" wrote in message
...
Tom Merkle wrote:
I've heard that there's already a somewhat standard coordinate system
for Mars (I mean an established Prime Meridian), but I haven't seen
any NASA press releases referring to the current LAT/LONG of Spirit.
Anybody know where it is?

To my best knowledge, Spirit is in Gusev Crater, 14.6 South and 184.7
West.
See for example:
http://www.giss.nasa.gov/tools/mars24/help/guide.html
However, this map shows some difference:
http://marsoweb.nas.nasa.gov/landing...s/final/Gusev/

Which brings me to another question-- who picked the Prime Meridian
for Mars and what is it based on? It better be good. (At least that
English dude picked his hometown, right?)

Mars has "areographic coordinate system" (Earth has geographic, Sun has
heliographic, Moon has selenographic etc. General term is
"planetographic".).
Prime meridian passes through crater names "Airy-O" in Mars.
See other meridians in different planets:
http://history.nasa.gov/SP-467/ch6.htm

I'm not sure the Sun or any of the gas giants really do simply because of
the lack of fixed surface features.




Matti Anttila
--
http://masa.net/

"Henry Spencer" wrote in message
...
In article ,
Andrew Gray wrote:
Greenwich runs through, IIRC, the site of the Royal Observatory, which
makes pretty good sense g

If you're British, that is. :-) The French and the Germans, to name just
two, had different opinions on the matter -- you can find old maps which
put zero longitude on Paris or Berlin instead. Only quite late in the
19th century was there grudging agreement to do things Britain's way.


And as someone pointed out, 20,000 Leagues under the Sea uses the Frence
Prime Meridian.

"Greg D. Moore \(Strider\)" wrote in
:

I'm not sure the Sun or any of the gas giants really do simply because of
the lack of fixed surface features.

Apparently Jupiter's solid core has some fixed features, which are
observable as radio emissions. It sounds like a standard in flux, though.

http://voyager.ftecs.com/sedr/overview.html