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Re: {MPML} 2012 DA14 a threat to geostationary satellites?

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  • Tony Dunn
    Hi Daniel, There was some discussion about this asteroid in this forum around Feb 26-28, 2012. Based on the observations available at that time, it was
    Message 1 of 24 , May 18, 2012
      Hi Daniel,
      There was some discussion about this asteroid in this forum around Feb
      26-28, 2012. Based on the observations available at that time, it was
      concluded that this rock will pass below Earth with no chance of striking
      Earth. Even monte carlo clones populating the uncertainty all passed below
      Earth.

      I just made a simulation of 2012 DA14's nominal path through the Earth
      system's geostationary region on Feb 15, 2013. The link below contains some
      screen shots. The left image is a top-down view perpendicular to the
      ecliptic plane. The right image is from within the ecliptic plane. The blue
      circle is Earth. The green path is 2012 DA14. The orange path is the orbit
      of geostationary satellites. The red paths show 2012 DA14's path as it
      appears to cross the geostationary plane as viewed from above.

      http://orbitsimulator.com/BA/2012DA14geos.GIF

      It doesn't look like the nominal trajectory has much chance of striking
      geostationary satellites. Perhaps it could hit a geosychronous satellite
      outside the geostationary plane?

      Tony

      ----- Original Message -----
      From: Daniel Fischer
      To: MPML@yahoogroups.com
      Sent: Friday, May 18, 2012 2:15 PM
      Subject: {MPML} 2012 DA14 a threat to geostationary satellites?



      http://news.nationalgeographic.com/news/2012/05/120517-asteroid-close-earth-satellites-danger-space-science
      claims this, and a calculation with http://ssd.jpl.nasa.gov/horizons.cgi -
      based on
      a 79-day arc - indeed brings this NEA to within 35,000 km of Earth's center.
      But:
      Does it pass thru the geostationary satellite *belt* (which is extended in z
      a bit)
      at any point? And if not: is the orbit still uncertain enough that it could,
      principle, hit a GEO sat? Or is this all just a misunderstanding?

      Dan
    • Jean Meeus
      Daniel wrote about 2012 DA14 :
      Message 2 of 24 , May 19, 2012
        Daniel wrote about 2012 DA14 :

        < and a calculation (...) based on a 79-day arc - indeed
        < brings this NEA to within 35,000 km of Earth's center.

        The last issue of the "List of close approaches to the Earth"
        by the Minor Planet Center gives, also based on a 79-day arc,
        a close approach of 0.0003012 a.u. to the Earth's center.
        This is 45,000 km, not 35,000.

        Jean Meeus


        [Non-text portions of this message have been removed]
      • wlodarczyk_i
        The JPL NASA gives on 2013 Feb. 15 19:25 TDB the minimum distance between the asteroid 2012 DA14 and the Earth of about 0.000181 AU, maximum=0.000354 AU and
        Message 3 of 24 , May 19, 2012
          The JPL NASA gives on 2013 Feb. 15 19:25 TDB the minimum distance between the asteroid
          2012 DA14 and the Earth of about 0.000181 AU, maximum=0.000354 AU and nominal=0.000234 AU.
          Using the OrbFit software I computed the nominal distance=0.000226 AU, i.e. about 33800 km
          from the center of the Earth - 191 observations were used.
          Best regards,
          Ireneusz Wlodarczyk
          553 Chorzow

          --- In mpml@yahoogroups.com, Jean Meeus <jmeeus@...> wrote:
          >
          > Daniel wrote about 2012 DA14 :
          >
          > < and a calculation (...) based on a 79-day arc - indeed
          > < brings this NEA to within 35,000 km of Earth's center.
          >
          > The last issue of the "List of close approaches to the Earth"
          > by the Minor Planet Center gives, also based on a 79-day arc,
          > a close approach of 0.0003012 a.u. to the Earth's center.
          > This is 45,000 km, not 35,000.
          >
          > Jean Meeus
          >
          >
          > [Non-text portions of this message have been removed]
          >
        • Aldo Vitagliano
          ... Yes, it could. But there is one thing I don t understand: why bother about this particular asteroid, considering that satellites do usually survive to
          Message 4 of 24 , May 19, 2012
            --- In mpml@yahoogroups.com, Daniel Fischer <dfischer@...> wrote:

            >
            > is the orbit still uncertain enough that it could,
            > principle, hit a GEO sat?
            >

            Yes, it could.

            But there is one thing I don't understand: why bother about this particular asteroid, considering that satellites do usually survive to thousands of chestnut- or apple-sized meteorites that would likely destroy them in the remote case of a collision ?... ;-)

            Aldo Vitagliano
          • George Herbert
            It would be useful to plot that with the uncertainty ellipse, to show if significant parts of the ellipse pass through GEO, and which direction the uncertainty
            Message 5 of 24 , May 19, 2012
              It would be useful to plot that with the uncertainty ellipse, to show if significant parts of the ellipse pass through GEO, and which direction the uncertainty is in relative to earth and GEO.

              Nominal is great but with that much uncertainty in how close the approach is...

              George William Herbert
              Sent from my iPhone

              On May 18, 2012, at 16:50, "Tony Dunn" <tony@...> wrote:

              > Hi Daniel,
              > There was some discussion about this asteroid in this forum around Feb
              > 26-28, 2012. Based on the observations available at that time, it was
              > concluded that this rock will pass below Earth with no chance of striking
              > Earth. Even monte carlo clones populating the uncertainty all passed below
              > Earth.
              >
              > I just made a simulation of 2012 DA14's nominal path through the Earth
              > system's geostationary region on Feb 15, 2013. The link below contains some
              > screen shots. The left image is a top-down view perpendicular to the
              > ecliptic plane. The right image is from within the ecliptic plane. The blue
              > circle is Earth. The green path is 2012 DA14. The orange path is the orbit
              > of geostationary satellites. The red paths show 2012 DA14's path as it
              > appears to cross the geostationary plane as viewed from above.
              >
              > http://orbitsimulator.com/BA/2012DA14geos.GIF
              >
              > It doesn't look like the nominal trajectory has much chance of striking
              > geostationary satellites. Perhaps it could hit a geosychronous satellite
              > outside the geostationary plane?
              >
              > Tony
              >
              > ----- Original Message -----
              > From: Daniel Fischer
              > To: MPML@yahoogroups.com
              > Sent: Friday, May 18, 2012 2:15 PM
              > Subject: {MPML} 2012 DA14 a threat to geostationary satellites?
              >
              >
              >
              > http://news.nationalgeographic.com/news/2012/05/120517-asteroid-close-earth-satellites-danger-space-science
              > claims this, and a calculation with http://ssd.jpl.nasa.gov/horizons.cgi -
              > based on
              > a 79-day arc - indeed brings this NEA to within 35,000 km of Earth's center.
              > But:
              > Does it pass thru the geostationary satellite *belt* (which is extended in z
              > a bit)
              > at any point? And if not: is the orbit still uncertain enough that it could,
              > principle, hit a GEO sat? Or is this all just a misunderstanding?
              >
              > Dan
              >
              >
              >
              >
              > ------------------------------------
              >
              > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
              >
              > Posts to this list or information found within may be freely used, with the stipulation that MPML and the originating author are cited as the source of the information.Yahoo! Groups Links
              >
              >
              >
            • amaury@spaceobs.com
              Because the title says it all, it uses the word threat Threat, fears, destructions, end of the world... damned, if you are not sensitive to these words, why
              Message 6 of 24 , May 19, 2012
                Because the title says it all, it uses the word "threat"
                Threat, fears, destructions, end of the world... damned, if you are
                not sensitive to these words, why be in the NEA business :) :) :)...

                I guess it makes for a good story, having a stupid satellite
                destroying a poor harmless asteroid... (pha)

                The fact is that satellites destroys themselves as they age, and if
                not, _we_ do (at least the american and chinese militaries). The more
                we send up, the more likely we start one day a chain reaction, and I
                assume that one of the consequence of a conflict between some space
                powers (let's say China, US, Russia) would be on a first strike, the
                destruction of the spy satellites of the other guy, meaning that apart
                from all the stupid consequences (stupid because war is always stupid,
                a recent example being something like how to waste 4000 billions of
                dollars in an useless war while debating if health plans are or not
                too expensive), the consequence is that space would not be useable
                anymore by humanity, and for a really long time.
                People suspect there may have been a case or two of satellites
                destroyed by "natural causes" but we are by far the most likely cause
                of "danger to satellites". And indeed by far, as Alan Harris pointed
                out a while ago, the threat is mostly by the very large number of very
                small stuff than by the occasional "large" meteoroid.

                Then again, it might be a good thing. The more I think of it, the more
                I think lobbies "tend" to lie. Do we really need to go to space ? for
                the price of all the weather satellites, we could have a lot of ground
                based measurement systems, really a lot. If the price of satellite
                launch would have to include deorbiting, would space be so interesting ?

                Can we live without communication satellites, can they be replaced by
                fiber optics on the ground? How does the prices compare, if we
                calculate honestly (including the price of deorbiting a geostationary
                satellite)

                It's about the same problem with nuclear energy. Clean, till there is
                a mishap, and inexpensive if you don't count the price of waste
                storage, dismantling of the power plant, and storage of the
                radioactive parts, etc...

                I am a bit away from the subject, but have seen various papers about
                NASA and how wonderful it would be to spend more billions of dollars
                for exploring whatever things in space. Do these guys really have
                their feet on the ground? While it would benefit some high tech
                businesses, and their shareholders, what about the people ? And what
                if that money was spent in the well being of these people instead ? (I
                don't know exactly how, but a few words come to mind, education,
                retirement plans, health plans, etc...).
                I guess sometimes we tend to live on our own small planet, and it's
                nice to look a bit outside, at what's happening in the world, the real
                one.
                Alain






                Aldo Vitagliano <alvitagl@...> a écrit :

                >
                >
                > --- In mpml@yahoogroups.com, Daniel Fischer <dfischer@...> wrote:
                >
                >>
                >> is the orbit still uncertain enough that it could,
                >> principle, hit a GEO sat?
                >>
                >
                > Yes, it could.
                >
                > But there is one thing I don't understand: why bother about this
                > particular asteroid, considering that satellites do usually survive
                > to thousands of chestnut- or apple-sized meteorites that would
                > likely destroy them in the remote case of a collision ?... ;-)
                >
                > Aldo Vitagliano
                >
                >
                >
                >
              • Alan W Harris
                Yes, well put, especially your use of a chestnut for size comparison. In English, a chestnut has a colloquial implication similar to a canard in French.
                Message 7 of 24 , May 19, 2012
                  Yes, well put, especially your use of a chestnut for size comparison. In
                  English, a "chestnut" has a colloquial implication similar to a "canard" in
                  French. As for "deja vu", see my discussion on MPML last time this
                  chestnut/canard circulated where I estimated the frequency of
                  satellite-killing chestnuts crossing the geosynchronous distance vis a vis
                  the frequency of 100-m sized asteroids. Your argument is correct, by a
                  huge factor, about a billion.

                  Alan

                  At 10:36 AM 5/19/2012, Aldo Vitagliano wrote:


                  >--- In mpml@yahoogroups.com, Daniel Fischer <dfischer@...> wrote:
                  >
                  > >
                  > > is the orbit still uncertain enough that it could,
                  > > principle, hit a GEO sat?
                  > >
                  >
                  >Yes, it could.
                  >
                  >But there is one thing I don't understand: why bother about this
                  >particular asteroid, considering that satellites do usually survive to
                  >thousands of chestnut- or apple-sized meteorites that would likely destroy
                  >them in the remote case of a collision ?... ;-)
                  >
                  >Aldo Vitagliano
                  >
                  >
                  >
                  >
                  >
                  >------------------------------------
                  >
                  >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                  >
                  >Posts to this list or information found within may be freely used, with
                  >the stipulation that MPML and the originating author are cited as the
                  >source of the information.Yahoo! Groups Links
                  >
                  >
                  >
                  *****************************************************************************
                  Alan Harris Phone: 818-790-8291
                  4603 Orange Knoll Ave.
                  La Cañada, CA 91011-3364
                  email: harrisaw@...
                  *****************************************************************************
                • Aldo Vitagliano
                  ... To make a plot would be a bit cumbersome for me, but I can answer this question in another way: As a representation of the uncertainty ellipsoid (actually
                  Message 8 of 24 , May 20, 2012
                    --- In mpml@yahoogroups.com, George Herbert <george.herbert@...> wrote:
                    >
                    > It would be useful to plot that with the uncertainty ellipse, to show if significant parts of the ellipse pass through GEO, and which direction the uncertainty is in relative to earth and GEO.
                    >
                    > Nominal is great but with that much uncertainty in how close the approach is...
                    >

                    To make a plot would be a bit cumbersome for me, but I can answer this question in another way:

                    As a representation of the uncertainty ellipsoid (actually an uncertainty line) I have taken 100 properly generated clones of the asteroid, at the moment each of them crosses the Earth's equatorial plane.
                    - The nominal one crosses the Equator at a geocentric distance of ca. 39,600 km.
                    - The closest one crosses the Equator at a distance of ca. 30,000 km.
                    - The farthest one crosses the Equator at a distance of ca. 55,400 km

                    The geocentric distance of geostationary satellites is 42,160 km

                    Aldo Vitagliano
                  • wlodarczyk_i
                    All virtual asteroids (VA) of 2012 DA14 computed according to 1-sigma variation criterion goes closer on 2013, February 15th, to the Earth then the radius of
                    Message 9 of 24 , May 20, 2012
                      All virtual asteroids (VA) of 2012 DA14 computed according to 1-sigma variation criterion
                      goes closer on 2013, February 15th, to the Earth then the radius of the geosynchronous orbit
                      i.e. about 42164 km from the center of the Earth.
                      All 191 observations of the asteroid 2012 DA14 and the OrbFit software were used.
                      Best regards,
                      Ireneusz Wlodarczyk,
                      553 Chorzow


                      --- In mpml@yahoogroups.com, "Aldo Vitagliano" <alvitagl@...> wrote:
                      >
                      >
                      > --- In mpml@yahoogroups.com, George Herbert <george.herbert@> wrote:
                      > >
                      > > It would be useful to plot that with the uncertainty ellipse, to show if significant parts of the ellipse pass through GEO, and which direction the uncertainty is in relative to earth and GEO.
                      > >
                      > > Nominal is great but with that much uncertainty in how close the approach is...
                      > >
                      >
                      > To make a plot would be a bit cumbersome for me, but I can answer this question in another way:
                      >
                      > As a representation of the uncertainty ellipsoid (actually an uncertainty line) I have taken 100 properly generated clones of the asteroid, at the moment each of them crosses the Earth's equatorial plane.
                      > - The nominal one crosses the Equator at a geocentric distance of ca. 39,600 km.
                      > - The closest one crosses the Equator at a distance of ca. 30,000 km.
                      > - The farthest one crosses the Equator at a distance of ca. 55,400 km
                      >
                      > The geocentric distance of geostationary satellites is 42,160 km
                      >
                      > Aldo Vitagliano
                      >
                    • Aldo Vitagliano
                      ... That s correct, but I was not mentioning the minimum distance of approach. I was talking about the distance at which the asteroid crosses the Equator plane
                      Message 10 of 24 , May 20, 2012
                        At 13:28 20/05/2012 -0000, wlodarczyk_i wrote:

                        >All virtual asteroids (VA)
                        >of 2012 DA14 computed according to 1-sigma variation criterion
                        > goes closer on 2013, February 15th, to the Earth than the radius of
                        > the geosynchronous orbit
                        > i.e. about 42164 km from the center of the Earth.

                        That's correct, but I was not mentioning the minimum distance of approach.
                        I was talking about the distance at which the asteroid crosses the Equator plane (where the geosynchronous satellites are located), which is a different thing.

                        Regards
                        Aldo
                      • Bill J Gray
                        When this 2012 DA14 threatening geosats came back to life, I meant to post a link to Alan s message of 26 March:
                        Message 11 of 24 , May 20, 2012
                          When this "2012 DA14 threatening geosats" came back to life,
                          I meant to post a link to Alan's message of 26 March:

                          http://tech.groups.yahoo.com/group/mpml/message/26823

                          ...wherein he pointed out that the real threat comes from small
                          stuff, not big stuff:

                          "...This is an utterly stupid red herring, however. Not only
                          are the odds astronomically small, but a rock the size of a marble
                          would be quite sufficient to kill a satellite; it doesn't take a
                          rock bigger than the satellite. Marble-sized rocks pass within
                          geosynchronous distance at a rate of about once per second --
                          around 100,000 per day (I actually worked that out roughly). So
                          yes, there is a meteoroid hazard to satellites, but it comes
                          overwhelmingly from the marbles, not the mountains."

                          100,000 objects per second, through a circle 40,000 km in
                          radius, works out to about 1.7 objects per day per square
                          kilometer. If your satellite had a cross-section of about
                          ten square meters, then you'd average one collision with
                          a marble once every 160 years or so.

                          The sizes of marbles and chestnuts wasn't given (for shame,
                          gentlemen!). I'd think of "marbles" as being one cm in diameter,
                          at least for the small ones. Chestnuts (at least the sort that
                          grow around here) are about three centimeters in diameter. I'd
                          think still smaller rocks could cause trouble. Consider: a
                          piece of lead half a centimeter in diameter, moving less than
                          the speed of sound (.3 km/s), known colloquially as a "bullet",
                          can do all sorts of damage. Rocks are much less dense than
                          lead, by a factor of four or five. But incoming rocks will
                          have a speed of at least a couple km/s, usually much more than
                          that. Even one a lot smaller than a marble or chestnut would,
                          I think, really ruin a satellite owner's day.

                          -- Bill
                        • wlodarczyk_i
                          All virtual asteroids (VA) of 2012 DA14 computed according to 1-sigma variation go to the geosynchronous orbit not closer then about 27000 km. All 191
                          Message 12 of 24 , May 21, 2012
                            All virtual asteroids (VA) of 2012 DA14 computed according to 1-sigma variation
                            go to the geosynchronous orbit not closer then about 27000 km.
                            All 191 observations of the asteroid 2012 DA14 and the OrbFit software were used.
                            Best regards,
                            Ireneusz Wlodarczyk,
                            553 Chorzow


                            --- In mpml@yahoogroups.com, "Aldo Vitagliano" <alvitagl@...> wrote:
                            >
                            >
                            > At 13:28 20/05/2012 -0000, wlodarczyk_i wrote:
                            >
                            > >All virtual asteroids (VA)
                            > >of 2012 DA14 computed according to 1-sigma variation criterion
                            > > goes closer on 2013, February 15th, to the Earth than the radius of
                            > > the geosynchronous orbit
                            > > i.e. about 42164 km from the center of the Earth.
                            >
                            > That's correct, but I was not mentioning the minimum distance of approach.
                            > I was talking about the distance at which the asteroid crosses the Equator plane (where the geosynchronous satellites are located), which is a different thing.
                            >
                            > Regards
                            > Aldo
                            >
                          • Bill J Gray
                            ... It s true that this is all of purely intellectual interest, and that the greater danger does come from marbles (whether one-centimeter metric marbles or
                            Message 13 of 24 , May 21, 2012
                              wlodarczyk_i wrote:
                              > All virtual asteroids (VA) of 2012 DA14 computed according to 1-sigma variation
                              > go to the geosynchronous orbit not closer then about 27000 km.
                              > All 191 observations of the asteroid 2012 DA14 and the OrbFit software were used.
                              > Best regards,
                              > Ireneusz Wlodarczyk,
                              > 553 Chorzow

                              It's true that this is all of purely intellectual interest, and that
                              the greater danger does come from marbles (whether one-centimeter metric
                              marbles or 3/8 inch "standard" marbles), and the whole "threat" to
                              geosats from big rocks is entirely meaningless. Despite all that, I
                              couldn't resist running the numbers.

                              Using all observations and the Find_Orb software, I'm finding that there
                              are "collisions" at about +1.03 and +3.02 sigmas. Use of all observations is
                              probably not a good idea here; three of them look iffy. But dropping them
                              doesn't change the results by much.

                              OrbFit uses different weighting, so your results (if you extended the
                              search out a few sigmas) would be slightly different.

                              I hope the above doesn't persuade any journalists on this list to
                              produce articles about the dire risk to geosats. Hence my adding [NO]
                              to the subject line.

                              -- Bill
                            • Dave Tholen
                              ... Only three? I threw out fifteen. The discovery observation is bad, as is the third observation on that same night. The entire set from code 950 on
                              Message 14 of 24 , May 21, 2012
                                > Use of all observations is probably not a good idea here; three of
                                > them look iffy.

                                Only three? I threw out fifteen. The discovery observation is bad, as
                                is the third observation on that same night. The entire set from code
                                950 on February 29 is systematically north by an arcsecond. There are
                                a few other scattered observations that stick out. Our own observations
                                from April 23 appear systematically west by a quarter arcsecond, which
                                is annoying, because we had hoped the PPMXL catalog would be better than
                                that.
                              • Bill J Gray
                                ... You re probably on the right track there. I will admit that I have no consistent policy on what observations I toss (*), but with 191 of them, it s hard
                                Message 15 of 24 , May 23, 2012
                                  Dave Tholen wrote:
                                  >> Use of all observations is probably not a good idea here; three of
                                  >> them look iffy.
                                  >
                                  > Only three? I threw out fifteen. The discovery observation is bad, as
                                  > is the third observation on that same night.

                                  You're probably on the right track there. I will admit that I have no
                                  consistent policy on what observations I toss (*), but with 191 of them,
                                  it's hard to see how throwing out 8% of them will do actual harm.

                                  > The entire set from code 950 on February 29 is systematically north
                                  > by an arcsecond. There are a few other scattered observations that stick out.

                                  It looks as if (950) had about an 18-second clock error. If observations
                                  were scarcer, we'd want the capability to mark those as having a large
                                  sigma on the observed time, though still good (probably!) in position.
                                  And ideally, we'd be able to solve for a single clock error value for
                                  all five positions in question... of course, for this case, we might
                                  as well just throw out those five positions; but I've seen lots of cases
                                  where being able to say, "I know the object really was at this RA/dec;
                                  I just don't know exactly _when_ it was there" would have been a useful
                                  constraint on the orbit.

                                  > Our own observations from April 23 appear systematically west by a
                                  > quarter arcsecond, which is annoying, because we had hoped the PPMXL
                                  > catalog would be better than that.

                                  I just ran some Monte Carlo clones, and for April 23, they're scattered
                                  over a circle about .3 arcsec across. It could be you and PPMXL are right
                                  and the nominal position was wrong. It might be interesting to see what
                                  reduction against UCAC-4 gives you.

                                  If I weighted your observations heavily, as I'd normally do, it would
                                  probably both shrink that circle and pull it toward your observations. In
                                  this case, though, I'm assuming that your observations at mag 23.5 are
                                  not quite as solid as your usual data. (Though I'm glad to see you went
                                  after it, both in late April and on 12 May. I've not checked yet, but
                                  I assume this will bring down the uncertainty for the recovery next February.)

                                  -- Bill

                                  (*) I'm open to suggestions on such a policy. The usual one seems to be
                                  "toss anything with residuals higher than X", which isn't terrible, but
                                  does have drawbacks.
                                • Aldo Vitagliano
                                  ... In this context it is interesting to compare the results obtained with and without adding to the observations the biases reported by the Neodys database.
                                  Message 16 of 24 , May 24, 2012
                                    --- In mpml@yahoogroups.com, Bill J Gray <pluto@...> wrote:
                                    ... but with 191 of them,
                                    > it's hard to see how throwing out 8% of them will do actual harm.
                                    >

                                    In this context it is interesting to compare the results obtained with and without adding to the observations the "biases" reported by the Neodys database. Normally, the shorter the observational arc, the heavier is the "weight" of the biases in affecting the result.
                                    In the case of 2012DA14, using the same observations "accepted" by Neodys (4 rejected), the same "weights" and adding the biases, I get a nominal minimum geocentric approach distance of 33950 km, quite consistent with the 0.0002265 AU (33880 km) given by Neodys.
                                    Without adding the biases, I get a nominal approach distance of 39300 km, larger than the former by about 1-sigma.

                                    Best regards
                                    Aldo
                                  • Dave Tholen
                                    ... We are not among the testers to whom the pre-release version of UCAC4 was sent, nor do we usually have enough of the brighter reference stars in our images
                                    Message 17 of 24 , May 24, 2012
                                      >> Our own observations from April 23 appear systematically west by a
                                      >> quarter arcsecond, which is annoying, because we had hoped the PPMXL
                                      >> catalog would be better than that.

                                      > I just ran some Monte Carlo clones, and for April 23, they're scattered
                                      > over a circle about .3 arcsec across. It could be you and PPMXL are right
                                      > and the nominal position was wrong. It might be interesting to see what
                                      > reduction against UCAC-4 gives you.

                                      We are not among the testers to whom the pre-release version of UCAC4
                                      was sent, nor do we usually have enough of the brighter reference
                                      stars in our images to use the less dense UCAC catalogs. The best
                                      we could likely do is to compare the PPMXL and UCAC4 catalogs over a
                                      sufficiently large field centered on each of our exposures, and we'd
                                      have to wait for the expected June release of the UCAC4 catalog.

                                      > If I weighted your observations heavily, as I'd normally do, it would
                                      > probably both shrink that circle and pull it toward your observations. In
                                      > this case, though, I'm assuming that your observations at mag 23.5 are
                                      > not quite as solid as your usual data. (Though I'm glad to see you went
                                      > after it, both in late April and on 12 May. I've not checked yet, but
                                      > I assume this will bring down the uncertainty for the recovery next February.)

                                      Our computed astrometric uncertainties are, in chronological order,
                                      0.17, 0.10, 0.07, 0.08, 0.10, 0.09, and 0.09 arcsec.

                                      > (*) I'm open to suggestions on such a policy. The usual one seems to be
                                      > "toss anything with residuals higher than X", which isn't terrible, but
                                      > does have drawbacks.

                                      We have been (slowly!) implementing the Peirce criterion for data rejection.
                                      It is superior to the Chauvenet criterion that we have been using, in that
                                      the Peirce criterion allows for multiple rejections. Marco describes it in
                                      our paper on 2009 BD, with references to some very old literature. Seems
                                      to have been largely forgotten; time to resurrect it!
                                    • wlodarczyk_i
                                      Using the OrbFit software I got similar results as Aldo Vitagliano for minimum geocentric close approache of the nominal orbit of asteroid 2012 DA14 with the
                                      Message 18 of 24 , May 24, 2012
                                        Using the OrbFit software I got similar results as Aldo Vitagliano
                                        for minimum geocentric close approache
                                        of the nominal orbit of asteroid 2012 DA14 with the Earth on 15/Feb/2013:
                                        with biases 0.00022646 AU = 33878 km
                                        without biases 0.00025908 AU = 38758 km
                                        It is still far from the MPC result:
                                        0.0003012 AU = 45060 km
                                        Best regards,
                                        Ireneusz Wlodarczyk
                                        553 Chorzow

                                        --- In mpml@yahoogroups.com, "Aldo Vitagliano" <alvitagl@...> wrote:
                                        >
                                        >
                                        > --- In mpml@yahoogroups.com, Bill J Gray <pluto@> wrote:
                                        > ... but with 191 of them,
                                        > > it's hard to see how throwing out 8% of them will do actual harm.
                                        > >
                                        >
                                        > In this context it is interesting to compare the results obtained with and without adding to the observations the "biases" reported by the Neodys database. Normally, the shorter the observational arc, the heavier is the "weight" of the biases in affecting the result.
                                        > In the case of 2012DA14, using the same observations "accepted" by Neodys (4 rejected), the same "weights" and adding the biases, I get a nominal minimum geocentric approach distance of 33950 km, quite consistent with the 0.0002265 AU (33880 km) given by Neodys.
                                        > Without adding the biases, I get a nominal approach distance of 39300 km, larger than the former by about 1-sigma.
                                        >
                                        > Best regards
                                        > Aldo
                                        >
                                      • Bill J Gray
                                        ... It occurred to me, after I wrote, that UCACx might not help much with an observation at mag 23.5. ... I first learned of the Peirce criterion from that
                                        Message 19 of 24 , May 24, 2012
                                          Dave Tholen wrote:

                                          > We are not among the testers to whom the pre-release version of UCAC4
                                          > was sent, nor do we usually have enough of the brighter reference
                                          > stars in our images to use the less dense UCAC catalogs.

                                          It occurred to me, after I wrote, that UCACx might not help much
                                          with an observation at mag 23.5.
                                          >
                                          > We have been (slowly!) implementing the Peirce criterion for data rejection.
                                          > It is superior to the Chauvenet criterion that we have been using, in that
                                          > the Peirce criterion allows for multiple rejections. Marco describes it in
                                          > our paper on 2009 BD, with references to some very old literature. Seems
                                          > to have been largely forgotten; time to resurrect it!

                                          I first learned of the Peirce criterion from that very paper. Just looked
                                          into it a little further... it looks promising. The basic idea actually looks
                                          pretty simple; it's the implementation of it that looks tricky. I can see why
                                          you're implementing it "slowly".

                                          -- Bill
                                        • Brian Skiff
                                          FWIW, Steve Levine here at Lowell made all-sky plots of mean proper motions for the fainter stars in UCAC2, UCAC3, and UCAC4 (the latter from a disc that
                                          Message 20 of 24 , May 24, 2012
                                            FWIW, Steve Levine here at Lowell made all-sky plots of
                                            mean proper motions for the fainter stars in UCAC2, UCAC3, and UCAC4
                                            (the latter from a disc that Norbert Zacharias sent him).
                                            UCAC2 shows the bulk solar-reflex motion of the field stars
                                            very clearly (and the solar apex and antapex locations); UCAC3 shows
                                            gibberish with scatter much larger than UCAC2 (we already knew UCAC3
                                            was rather poor); the UCAC4 plot is nearly identical to the UCAC2 plot.
                                            So at least in terms of the precision of the proper motions, it looks
                                            as though UCAC4 gets back to the quality of UCAC2. That's good news!
                                            In use on a star-by-star basis, I have not found PPMXL to be
                                            any good at all. Since it uses USNO-B1.0 as the 'seed' star-list,
                                            if B1.0 is no good, generally neither is PPMXL. The GIGO law still
                                            applies! Basically the linkage of the epochs involved with B1.0 and
                                            2MASS is just as bad as with B1.0. An easy way to see this is to
                                            grab a small chunk of sky using VizieR (PPMXL is item I/317) and look
                                            down the list to see what the general run of proper motions is.
                                            An amazing number of the stars have motions >> 50 mas/year, whereas
                                            for the very faint stars (statistically very distant) involved
                                            you expect essentially zero motion plus whatever the errors of the
                                            catalogue are (the authors claim < 10 mas/year). Instead what you see
                                            are zillions of stars that ought to be in catalogues of
                                            large-proper-motion objects. Instead _none_ of them is, because the
                                            PPMXL motions (and thus positions) are no good.
                                            Occasionally I have found cases where PPMXL gets a star right
                                            when B1.0 does not. I suppose for global astrometric solutions,
                                            if you can iterate to throw out half or more of the stars, maybe things
                                            would be okay, but one wonders whether this leaves you offset from the
                                            nominal ICRS reference frame.
                                            For very faint stars (only), probably still the best single-source
                                            all-sky astrometry would come from USNO-B1.0 _without_applying_
                                            _proper_motions_. This time of year, in the north, I would definitely
                                            try to use SDSS DR7. (Avoid SDSS DR8 since both the astrometry and
                                            the photometry is messed-up there.) I wonder if one could use
                                            a subset of the WISE catalogue of objects with small internal errors
                                            (probably 0".10 and smaller). That has been adjusted to be very close
                                            to the ICRS and the mean epoch is about 2010.5. Differentially, at
                                            least, I know that the astrometric errors are < 0".1 for the stars
                                            with good S/N. Other recent-epoch sources that reach to faint limits,
                                            but covering only small patches of sky, include the UKIDSS and
                                            2MASS 6x catalogues.


                                            \Brian



                                            > > I just ran some Monte Carlo clones, and for April 23, they're scattered
                                            > > over a circle about .3 arcsec across. It could be you and PPMXL are right
                                            > > and the nominal position was wrong. It might be interesting to see what
                                            > > reduction against UCAC-4 gives you.
                                            >
                                            > We are not among the testers to whom the pre-release version of UCAC4
                                            > was sent, nor do we usually have enough of the brighter reference
                                            > stars in our images to use the less dense UCAC catalogs. The best
                                            > we could likely do is to compare the PPMXL and UCAC4 catalogs over a
                                            > sufficiently large field centered on each of our exposures, and we'd
                                            > have to wait for the expected June release of the UCAC4 catalog.
                                          • Dave Tholen
                                            ... We typically reject anything with a residual of 0.5 arcsec or larger. Yes, I know such a practice would make a statistician cringe, but as the saying
                                            Message 21 of 24 , May 24, 2012
                                              > Occasionally I have found cases where PPMXL gets a star right
                                              > when B1.0 does not. I suppose for global astrometric solutions,
                                              > if you can iterate to throw out half or more of the stars, maybe things
                                              > would be okay, but one wonders whether this leaves you offset from the
                                              > nominal ICRS reference frame.

                                              We typically reject anything with a residual of 0.5 arcsec or
                                              larger. Yes, I know such a practice would make a statistician
                                              cringe, but as the saying goes, the proof of the pudding is in
                                              the eating, and we've been getting decent results. The open
                                              question is the level of bias, and is that bias random in
                                              the all-sky sense? For now, until we have enough experience
                                              to suggest otherwise, we're assuming the same level of bias
                                              as for 2MASS, namely 20 mas. Random errors of the individual
                                              stars are not any better than for USNO-B1.0, at least in the
                                              magnitude range we normally use. Curiously, B1.0 had stated
                                              uncertainties for star positions as large as 999 mas, but the
                                              largest in the PPMXL catalog is 210 mas. Basically we ignore
                                              the stated uncertainties.

                                              Hang in there, Gaia's coming.
                                            • Dave Tholen
                                              ... Forgot to mention in my previous response that when I built a custom version of PPMXL for asteroid use, I compiled a list of anomalies. The catalog
                                              Message 22 of 24 , May 24, 2012
                                                > An amazing number of the stars have motions >> 50 mas/year

                                                Forgot to mention in my previous response that when I built a
                                                custom version of PPMXL for asteroid use, I compiled a list of
                                                anomalies. The catalog contains 7226 coordinates with proper
                                                motions in excess of 5000 mas/year. Barnard's Star is in the
                                                catalog twice. PPMXL carries over the problem of bogus doubles
                                                in the B1.0, but a little surprised that Barnard's Star is one
                                                of them.
                                              • John Menke
                                                A number of us on the US East Coast attempted to observe/measure the June 13 Pluto occultation event. Many were clouded out, but here in MD I fortunately had
                                                Message 23 of 24 , Jun 18 6:37 AM
                                                  A number of us on the US East Coast attempted to observe/measure the
                                                  June 13 Pluto occultation event. Many were clouded out, but here in MD
                                                  I fortunately had excellent conditions but observed a miss. My question
                                                  is whether anyone can comment on what happened to the shadow: where did
                                                  it go? Were the predictions in serious error?

                                                  John Menke
                                                  menkescientific.com


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