From spencer Thu Nov  2 10:24:26 1995
From spencer Thu Nov  2 10:24:26 1995
To: oleroemer
Subject: Jupiter viewing times
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I just got this from John Rogers, leader of the Jupiter section
of the British Astronomical Association.  It's not directly
relevant to the Satellites Discipline, but there might be
someone on the list who can help with these important observations,
so here's the information...

Our last hope for Io remote sensing during the December Io flyby,
a high-res equatorial scan with the radiometer, will not be done
after all.  However, as far as I know, the particles and fields
measurements are still likely to take place, and will return very
valuable data.

John.

_____________________________________________

NOTE FOR IJW, sent Oct.31:
LONGITUDE OF PROBE ENTRY SITE

So far I have only seen the Probe entry longitude given in System III.
However, in this latitude region on the NEBs edge, everything moves
with System I - all large and small features, from the visible
cloudtops down to the 5-micron regions.  System I (\1) diverges from
System III (\3) by 7.4 degrees/day.  Therefore it is essential to
track the Probe entry site in System I.

Below will be an adaptation of Glenn's table of viewing times, for \1
= 7.4.  This is the point of entry, around 50 nanobars, based on the
value of \3 = 5.0 given by the Galileo team (by coincidence, \1 = \3 a
few hours before entry).  However after 2 min deceleration, descent
through the cloud layers will be at \1 ~ 4.0 (+/- 1 degree).  This
longitude is deduced from the Galileo project statement that the Probe
will be fully entrained by local winds after E + 2 min, and will cross
the terminator at E + 42 min.  (The stated times appear to be UT at
the spacecraft, rather than Earth-received time).  If anyone sees any
errors in these figures, please let me know.  Thus:
  -----------------------------------------------------
                         Entry      E+2m       E+42m
                                  (0.1 bar)   (12 bar)
                         -------    -------    -------
  Time UT at spacecraft   22:04     22:06      22:46
  Time UT at Earth        22:56     22:58      23:38

  Longitude Sys.I          7.4       4.0        4.0
  Longitude Sys.III        5.0       1.6        1.4

  Latitude 'centric       +6.6        ?          ?
  Latitude 'graphic       +7.5        ?          ?
  -----------------------------------------------------

In July-August, \1 = 4 happened to be the location of a large,
persistent 'NEBs dark projection' (visible), presumably a 'hotspot' (5
microns).  This was one of only two such features on an otherwise
messy NEBs; we will try to establish whether it is still there.
However, even if such a feature appears stable, it can change suddenly
within 1-2 days, and the probe might fly through a billowing white
updraft and/or an adjacent dark 'hotspot'.  Therefore, extrapolated
data will be no substitute for observations on the exact day of the
Galileo entry.

-- John Rogers
   British Astronomical Association.

  ------------------------------------------------------------
      UT date         Jupiter-Sun     PES (\1=7.4) CM
                      Angle (deg.)    Crossing Time (UT)
  ------------------------------------------------------------
     Dec.  1.0           14.1                 7:42
                                             17:33

     Dec.  2.0           13.3                 3:24
                                             13:15
                                             23:05

     Dec.  3.0           12.6                 8:56
                                             18:47

     Dec.  4.0           11.7                 4:37
                                             14:28

     Dec.  5.0           11.0                 0:18
                                             10:09
                                             20:00

     Dec.  6.0           10.2                 5:50
                                             15:41

     Dec.  7.0            9.4                 1:32
                                             11:23
                                             21:13
    
     Dec.  8.0            8.6                 7:04
                                             16:54

     Dec.  9.0            7.8                 2:45
                                             12:36
                                             22:27

     Dec. 10.0            7.0                 8:17
  ------------------------------------------------------------
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