COMET 103P/HARTLEY-2
------------------
John Pazmino
NYSkies Astronomy Inc
nyskies@nyskies.org
www.nyskies.org
2010 September 10 initial
2010 September 23 current
Introduction
----------
The 2010 return of comet Hartley-2, or comet 103P/Hartley-2,
stirred up heavy excitement among home astronomers. This comet is
already in mid September 2010 growing in luminance pretty much as
expected, based on previous apparitions. If this trend continues,
Hartley-2 will be a binocular target in New York and a naked-eye
target from a darksky location. It will surely be a highlight in
regular starviewing sessions thruout the fall of 2010 and may generate
enough public interest to have extra sessions primarily for the comet.
I gather here information about the comet, plus explanation of a
couple topics not adequately treated elsewhere. Some items here are
available in other sources but are here together in one place.
History
-----
Comet Hartley-2 was discovered on 15 March 1986 by Malcolm Hartley
at Siding Spring Observatory, Australia. It rounded perihelion, on 5
June 1985. It was found to have a closed orbit with a period of 6.27
years, but there was no prior record of seeing it.
Hartley-2 was sent into a trajectory passing near to Earth by a
close pass by Jupiter 2 November 1982, which accounts for not seeing
it before this visit. The comet faded from view by 2 June 1986.
It was recovered on 9 July 1991 for its second visit to the Sun.
It rounded perihelion on 2 September 1991 and receded from view by 4
May 1992. On 19 December 1993, between the 2nd and 3rd visit, Hartley-
2 suffered an other orbit mutation from Jupiter.
It returned into view in its new orbit on 2 May 1997 and passed
perihelion on 21 December 1997. At this return it earned its own
periodic comet designation, 103P/Hartley-2. By 12 April 1999 it
receded too far and grew too dim to be seen.
Hartley-2 returned for its 4th visit, being sighted on 20
September 2004. It rounded perihelion on 17 May 2004. We waved it
good-bye on 15 April 2005.
The next visit is now in 2010, after being recovered on 5 May
2008. This return is the best of all because Hartley-2 passes thru the
evening and night sky in high altitude (for northern observers). It is
also passing close to earth, 0.121 AU, on 20 October 2010. Perihelion,
1.058 AU, is on 28 October 2010.
Apparitions
---------
The track of 103P for two months before thru two months after each
perihelion is given below. This span is NOT the period of best
observation, but is a sample slice of the comet's track in the sky
running toward and away from each perihelion.
The path was computed by JPL's HORIZONS ephemeris. I did some
cosmetic arrangement and editing. Appreciate that other ephemeris
methods may give slightly different figures.
---------------
1985 apparition
---------------
EPOCH= 2446240.5 = 1985-Jun-24.0000000 (CT) RMSW= n.a.
EC= .719838 QR= .951617 TP= 2446221.369
OM= 226.8541 W= 174.8108 IN= 9.252800000000001
A= 3.396666928419986 MA= 3.0120508641739 ADIST= 5.841716856839971
PER= 6.2601919016158 N= .157443462 ANGMOM= .02200677
DAN= 5.78084 DDN= .95325 L= 41.7320577
B= .8332648 TP= 1985-Jun-04.8690000
****************************************************************
Date, 0h UT R.A. (J2000.0) DEC Sun AU Earth AU Elong Cns
----------- ------------------ -------- -------- ------- ---
1985-Apr-05 23 21 03 +01 36 31 1.290961 2.138728 24.0291 Psc
1985-Apr-10 23 38 48 +03 18 54 1.246678 2.091732 24.1361 Psc
1985-Apr-15 23 57 14 +05 04 04 1.203888 2.048405 24.0611 Psc
1985-Apr-20 00 16 24 +06 51 01 1.162937 2.009158 23.8075 Psc
1985-Apr-25 00 36 18 +08 38 35 1.124218 1.974389 23.3814 Psc
1985-Apr-30 00 56 58 +10 25 18 1.088171 1.944472 22.7930 Psc
1985-May-05 01 18 24 +12 09 33 1.055276 1.919728 22.0572 Psc
1985-May-10 01 40 34 +13 49 37 1.026041 1.900378 21.1950 Psc
1985-May-15 02 03 25 +15 23 39 1.000988 1.886518 20.2318 Ari
1985-May-20 02 26 54 +16 49 48 0.980619 1.878161 19.1960 Ari
1985-May-25 02 50 53 +18 06 20 0.965389 1.875244 18.1187 Ari
1985-May-30 03 15 15 +19 11 41 0.955668 1.877644 17.0326 Ari
1985-Jun-04 03 39 49 +20 04 42 0.951707 1.885169 15.9718 Tau
1985-Jun-09 04 04 25 +20 44 38 0.953610 1.897538 14.9711 Tau
1985-Jun-14 04 28 53 +21 11 09 0.961327 1.914388 14.0629 Tau
1985-Jun-19 04 53 00 +21 24 23 0.974656 1.935324 13.2749 Tau
1985-Jun-24 05 16 38 +21 24 52 0.993265 1.959948 12.6290 Tau
1985-Jun-29 05 39 37 +21 13 25 1.016726 1.987873 12.1404 Tau
1985-Jul-04 06 01 51 +20 51 12 1.044548 2.018712 11.8188 Ori
1985-Jul-09 06 23 14 +20 19 27 1.076212 2.052038 11.6688 Gem
1985-Jul-14 06 43 44 +19 39 28 1.111205 2.087395 11.6899 Gem
1985-Jul-19 07 03 20 +18 52 32 1.149033 2.124330 11.8778 Gem
1985-Jul-24 07 22 00 +17 59 52 1.189243 2.162417 12.2265 Gem
1985-Jul-29 07 39 47 +17 02 36 1.231425 2.201268 12.7300 Gem
1985-Aug-03 07 56 40 +16 01 45 1.275215 2.240510 13.3840 Cnc
1985-Aug-08 08 12 44 +14 58 11 1.320299 2.279747 14.1863 Cnc
1985-Aug-13 08 28 00 +13 52 37 1.366403 2.318578 15.1347 Cnc
1985-Aug-18 08 42 32 +12 45 43 1.413293 2.356620 16.2270 Cnc
1985-Aug-23 08 56 21 +11 38 00 1.460772 2.393538 17.4600 Cnc
1985-Aug-28 09 09 30 +10 29 58 1.508670 2.429048 18.8305 Cnc
*****************************************************************
In this first visit to Earth, Hartley-2 was angularly near the Sun
during its perihelion pass. In fact it wasn't seen in this span. It
was first found in March of 1986, 8-9 months after perihelion, deep
into its outward run.
---------------
1991 apparition
---------------
EPOCH= 2448520.5 = 1991-Sep-21.0000000 (CT) RMSW= n.a.
EC= .719493 QR= .9532969999999999 TP= 2448511.1514
OM= 226.7846 W= 174.8957 IN= 9.251799999999999
A= 3.398478469343011 MA= 1.4706992386261 ADIST= 5.843659938686023
PER= 6.2652006819822 N= .157317592 ANGMOM= .022023978
DAN= 5.78482 DDN= .95488 L= 41.7463562
B= .8195794 TP= 1991-Sep-11.6514000
*****************************************************************
Date, 0h UT R.A. (J2000.0) DEC Sun AU Earth AU Elong Cns
----------- ------------------ -------- -------- ------- ---
1991-Jul-01 00 26 20 +16 24 40 1.399991 1.032892 86.1610 Psc
1991-Jul-06 00 46 37 +18 41 25 1.353391 0.977027 85.4740 Psc
1991-Jul-11 01 08 50 +20 58 32 1.307647 0.926957 84.4268 Psc
1991-Jul-16 01 33 11 +23 12 19 1.263003 0.883208 83.0202 Psc
1991-Jul-21 01 59 45 +25 17 56 1.219745 0.846293 81.2702 Ari
1991-Jul-26 02 28 34 +27 09 37 1.178202 0.816629 79.2152 Ari
1991-Jul-31 02 59 24 +28 41 07 1.138748 0.794503 76.9188 Ari
1991-Aug-05 03 31 52 +29 46 31 1.101805 0.780036 74.4680 Tau
1991-Aug-10 04 05 15 +30 21 25 1.067838 0.773162 71.9649 Tau
1991-Aug-15 04 38 47 +30 23 52 1.037344 0.773632 69.5143 Aur
1991-Aug-20 05 11 39 +29 54 45 1.010839 0.780991 67.2110 Aur
1991-Aug-25 05 43 12 +28 57 26 0.988831 0.794572 65.1336 Aur
1991-Aug-30 06 12 57 +27 36 51 0.971793 0.813542 63.3403 Gem
1991-Sep-04 06 40 42 +25 58 31 0.960125 0.836958 61.8685 Gem
1991-Sep-09 07 06 20 +24 07 46 0.954122 0.863843 60.7365 Gem
1991-Sep-14 07 29 57 +22 09 08 0.953940 0.893257 59.9459 Gem
1991-Sep-19 07 51 40 +20 06 21 0.959584 0.924306 59.4869 Gem
1991-Sep-24 08 11 39 +18 02 11 0.970906 0.956136 59.3457 Cnc
1991-Sep-29 08 30 04 +15 58 41 0.987620 0.987950 59.5078 Cnc
1991-Oct-04 08 47 05 +13 57 18 1.009331 1.019026 59.9611 Cnc
1991-Oct-09 09 02 47 +11 59 08 1.035569 1.048756 60.6946 Cnc
1991-Oct-14 09 17 17 +10 04 53 1.065828 1.076675 61.6964 Cnc
1991-Oct-19 09 30 40 +08 15 01 1.099592 1.102413 62.9553 Leo
1991-Oct-24 09 43 01 +06 29 48 1.136360 1.125670 64.4622 Leo
1991-Oct-29 09 54 24 +04 49 23 1.175667 1.146193 66.2113 Sex
1991-Nov-03 10 04 51 +03 13 53 1.217088 1.163785 68.2001 Sex
1991-Nov-08 10 14 23 +01 43 25 1.260244 1.178347 70.4268 Sex
1991-Nov-13 10 23 02 +00 18 04 1.304805 1.189880 72.8887 Sex
1991-Nov-18 10 30 47 -01 02 05 1.350484 1.198442 75.5838 Sex
1991-Nov-23 10 37 39 -02 17 01 1.397032 1.204127 78.5118 Sex
1991-Nov-28 10 43 38 -03 26 40 1.444241 1.207049 81.6761 Sex
******************************************************************
In this apparition Hartley-2 was comfortably far angularly from
the Sun and linearly near Earth for good viewing. It was then in the
midnight thru dawn sky.
---------------
1997 apparition
---------------
EPOCH= 2450800.5 = 1997-Dec-18.0000000 (CT) RMSW= n.a.
EC= .700379 QR= 1.031723 TP= 2450804.5174
OM= 219.9541 W= 180.7225 IN= 13.6188
A= 3.443426862603088 MA= 359.38032659955 ADIST= 5.855130725206177
PER= 6.3899064050375 N= .154247374 ANGMOM= .022784309
DAN= 5.85404 DDN= 1.03176 L= 40.6562881
B= -.1701163 TP= 1997-Dec-22.0174000
*****************************************************************
Date, 0h UT R.A. (J2000.0) DEC Sun AU Earth AU Elong Cns
----------- ------------------ -------- -------- ------- ---
1997-Oct-04 18 47 40 -04 32 52 1.479567 1.062050 91.6353 Sct
1997-Oct-09 18 53 59 -05 13 37 1.436048 1.059197 88.4493 Sct
1997-Oct-14 19 01 26 -05 52 38 1.393332 1.054623 85.4865 Aql
1997-Oct-19 19 09 59 -06 29 35 1.351606 1.048186 82.7432 Aql
1997-Oct-24 19 19 39 -07 04 07 1.311088 1.039823 80.2169 Aql
1997-Oct-29 19 30 26 -07 35 53 1.272028 1.029505 77.9093 Aql
1997-Nov-03 19 42 21 -08 04 30 1.234704 1.017235 75.8239 Aql
1997-Nov-08 19 55 23 -08 29 36 1.199425 1.003077 73.9647 Aql
1997-Nov-13 20 09 34 -08 50 51 1.166527 0.987186 72.3348 Cap
1997-Nov-18 20 24 54 -09 07 54 1.136370 0.969831 70.9368 Cap
1997-Nov-23 20 41 24 -09 20 21 1.109328 0.951354 69.7764 Aqr
1997-Nov-28 20 59 05 -09 27 45 1.085781 0.932143 68.8629 Aqr
1997-Dec-03 21 17 58 -09 29 36 1.066095 0.912639 68.2064 Aqr
1997-Dec-08 21 38 02 -09 25 27 1.050606 0.893354 67.8164 Cap
1997-Dec-13 21 59 15 -09 14 47 1.039601 0.874897 67.6982 Aqr
1997-Dec-18 22 21 35 -08 57 09 1.033295 0.857967 67.8534 Aqr
1997-Dec-23 22 44 57 -08 32 03 1.031816 0.843292 68.2800 Aqr
1997-Dec-28 23 09 16 -07 59 08 1.035193 0.831587 68.9702 Aqr
1998-Jan-02 23 34 22 -07 18 12 1.043358 0.823532 69.9062 Aqr
1998-Jan-07 00 00 03 -06 29 30 1.056147 0.819759 71.0568 Cet
1998-Jan-12 00 26 06 -05 33 36 1.073315 0.820852 72.3754 Psc
1998-Jan-17 00 52 16 -04 31 28 1.094553 0.827319 73.8037 Cet
1998-Jan-22 01 18 16 -03 24 24 1.119511 0.839530 75.2775 Cet
1998-Jan-27 01 43 54 -02 13 57 1.147815 0.857701 76.7317 Cet
1998-Feb-01 02 08 57 -01 01 51 1.179087 0.881888 78.1049 Cet
1998-Feb-06 02 33 14 +00 10 06 1.212956 0.912018 79.3415 Cet
1998-Feb-11 02 56 38 +01 20 24 1.249071 0.947952 80.3941 Cet
1998-Feb-16 03 19 03 +02 27 41 1.287105 0.989497 81.2278 Cet
1998-Feb-21 03 40 28 +03 31 01 1.326763 1.036398 81.8213 Tau
1998-Feb-26 04 00 54 +04 29 41 1.367778 1.088348 82.1662 Tau
*****************************************************************
The 1997 return was a good one with Hartley-2 in evening to night
sky with reasonably approach to Earth. The comet received its number
as a new periodic comet, 103P. Note well that this return was on a new
orbit resulting from the meet with Jupiter in 1993. It was not a
simple prolongation from the 1991 return.
---------------
2004 apparition
---------------
EPOCH= 2454179.5 = 2007-Mar-20.0000000 (CT) Residual RMS= .59218
EC= .6954407870491051 QR= 1.055939352573553 TP= 2453140.644676941
OM= 219.7768134530225 W= 181.2914244208019 IN= 13.63163550116112
A= 3.467106912782197 MA= 158.60186594728 ADIST= 5.87827447299084
PER= 6.4559335724536 N= .15266983 ANGMOM= .023016657
DAN= 5.87487 DDN= 1.05605 L= 41.0318716
B= -.3043369 TP= 2004-May-15.1446769
*****************************************************************
Date, 0h UT R.A. (J2000.0) DEC Sun AU Earth AU Elong Cns
----------- ------------------ -------- -------- ------- ---
2004-Mar-01 22 08 17 -03 07 36 1.471735 2.432035 11.0298 Aqr
2004-Mar-06 22 23 33 -01 53 42 1.428587 2.386496 11.5870 Aqr
2004-Mar-11 22 39 17 -00 35 59 1.386285 2.342101 12.0668 Aqr
2004-Mar-16 22 55 31 +00 45 15 1.345026 2.299230 12.4486 Psc
2004-Mar-21 23 12 16 +02 09 36 1.305035 2.258237 12.7180 Psc
2004-Mar-26 23 29 34 +03 36 27 1.266565 2.219499 12.8654 Psc
2004-Mar-31 23 47 26 +05 05 07 1.229899 2.183408 12.8854 Psc
2004-Apr-05 00 05 52 +06 34 43 1.195348 2.150347 12.7779 Psc
2004-Apr-10 00 24 53 +08 04 22 1.163250 2.120659 12.5475 Psc
2004-Apr-15 00 44 30 +09 32 58 1.133963 2.094613 12.2035 Psc
2004-Apr-20 01 04 41 +10 59 20 1.107859 2.072426 11.7588 Psc
2004-Apr-25 01 25 25 +12 22 11 1.085308 2.054294 11.2295 Psc
2004-Apr-30 01 46 40 +13 40 10 1.066666 2.040386 10.6362 Psc
2004-May-05 02 08 22 +14 52 02 1.052253 2.030825 10.0039 Ari
2004-May-10 02 30 25 +15 56 35 1.042336 2.025661 9.3625 Ari
2004-May-15 02 52 46 +16 52 47 1.037106 2.024852 8.7453 Ari
2004-May-20 03 15 17 +17 39 45 1.036671 2.028297 8.1857 Ari
2004-May-25 03 37 50 +18 16 50 1.041038 2.035876 7.7158 Tau
2004-May-30 04 00 18 +18 43 41 1.050119 2.047447 7.3628 Tau
2004-Jun-04 04 22 33 +19 00 13 1.063735 2.062839 7.1460 Tau
2004-Jun-09 04 44 29 +19 06 39 1.081633 2.081829 7.0732 Tau
2004-Jun-14 05 05 59 +19 03 22 1.103501 2.104119 7.1395 Tau
2004-Jun-19 05 26 56 +18 50 58 1.128986 2.129387 7.3298 Tau
2004-Jun-24 05 47 18 +18 30 12 1.157722 2.157313 7.6251 Tau
2004-Jun-29 06 06 59 +18 01 51 1.189335 2.187581 8.0083 Ori
2004-Jul-04 06 25 58 +17 26 50 1.223463 2.219874 8.4682 Gem
2004-Jul-09 06 44 14 +16 46 00 1.259766 2.253837 9.0001 Gem
2004-Jul-14 07 01 47 +16 00 12 1.297926 2.289075 9.6051 Gem
2004-Jul-19 07 18 36 +15 10 11 1.337655 2.325199 10.2876 Gem
2004-Jul-24 07 34 42 +14 16 43 1.378696 2.361849 11.0541 Gem
2004-Jul-29 07 50 07 +13 20 26 1.420819 2.398694 11.9127 Gem
*****************************************************************
This was the lousiest visit of all! 103P angularly hugged the Sun
at a remote distance from Earth.. Only a few observations were made
compared to the 1997 return.
In its current orbit, until the next mutation by Jupiter in 2054,
Hartley-2 alternates between a good visit with perihelia in fall or
winter and awful ones with perihelia in spring or summer. This comes
from the 6-1/2 year period that puts Earth on opposite sides of the
Sun relative to the comet for each apparition.
The next round in 2010 is specially favorable, such that for the
first time in its known life 103P may reach naked-eye visibility.
2010 apparition
-------------
103P was recovered at Paranal Observatory on 5 May 2008 and
monitored lightly there after. On 12 March 2010 regular and frequent
observations began. The comet is under intense scrutiny to better plan
for the meet with Deep Impact in fall of 2010. Home observations began
in July-August when the comet came into reach of medium-size scopes.
-----------------------------------------
Orbital elements are taken from MPC 70362
Epoch 2010 Oct. 11.0 TT = JDT 2455480.5
Peri T 2010 Oct 28.2670 TT
Peri AU 1.058693 (2000.0)
M D M 0.1523112 Arg Peri 181.2025
S M A 3.472547 Asc Node 219.7600
Excenty 0.695125 Inclintn 13.6184
Period 6.47y
-----------------------------------------------
Date 0hUT R A (2000) Decl Earth Sun Elong Mag
---------- -------------------- ------ ------ ----- ---
2010 09 01 22 50 33.1 +37 53 22 0.3935 1.3120 133.6 8.8
2010 09 02 22 51 40.5 +38 24 02 0.3853 1.3044 133.5 8.7
2010 09 03 22 52 51.6 +38 54 58 0.3771 1.2970 133.3 8.6
2010 09 04 22 54 06.6 +39 26 10 0.3690 1.2896 133.2 8.5
2010 09 05 22 55 26.0 +39 57 38 0.3610 1.2822 133.1 8.4
2010 09 06 22 56 50.1 +40 29 23 0.3531 1.2750 132.9 8.3
2010 09 07 22 58 19.5 +41 01 26 0.3453 1.2678 132.7 8.3
2010 09 08 22 59 54.6 +41 33 46 0.3375 1.2606 132.6 8.2
2010 09 09 23 01 35.9 +42 06 26 0.3299 1.2536 132.4 8.1
2010 09 10 23 03 24.2 +42 39 24 0.3223 1.2467 132.2 8.0
2010 09 11 23 05 20.0 +43 12 42 0.3149 1.2398 132.0 7.9
2010 09 12 23 07 24.1 +43 46 21 0.3075 1.2330 131.8 7.8
2010 09 13 23 09 37.3 +44 20 22 0.3002 1.2263 131.6 7.7
2010 09 14 23 12 00.4 +44 54 44 0.2930 1.2197 131.4 7.6
2010 09 15 23 14 34.4 +45 29 28 0.2858 1.2132 131.2 7.5
2010 09 16 23 17 20.4 +46 04 34 0.2788 1.2068 131.0 7.4
2010 09 17 23 20 19.4 +46 40 03 0.2718 1.2004 130.7 7.3
2010 09 18 23 23 32.7 +47 15 53 0.2649 1.1942 130.5 7.2
2010 09 19 23 27 01.8 +47 52 03 0.2582 1.1881 130.3 7.1
2010 09 20 23 30 48.1 +48 28 32 0.2515 1.1821 130.1 7.0
2010 09 21 23 34 53.3 +49 05 18 0.2448 1.1762 129.9 6.9
2010 09 22 23 39 19.3 +49 42 17 0.2383 1.1704 129.7 6.8
2010 09 23 23 44 08.2 +50 19 24 0.2319 1.1648 129.5 6.7
2010 09 24 23 49 22.1 +50 56 34 0.2255 1.1592 129.3 6.5
2010 09 25 23 55 03.5 +51 33 39 0.2193 1.1538 129.1 6.4
2010 09 26 00 01 15.2 +52 10 29 0.2132 1.1485 128.9 6.3
2010 09 27 00 08 00.0 +52 46 51 0.2071 1.1433 128.7 6.2
2010 09 28 00 15 21.0 +53 22 30 0.2012 1.1383 128.5 6.1
2010 09 29 00 23 21.4 +53 57 07 0.1954 1.1333 128.3 6.0
2010 09 30 00 32 04.5 +54 30 17 0.1897 1.1285 128.1 5.9
-------------------------------------------------------------
2010 10 01 00 41 33.7 +55 01 31 0.1842 1.1239 127.9 5.8
2010 10 02 00 51 52.1 +55 30 15 0.1788 1.1194 127.7 5.7
2010 10 03 01 03 02.4 +55 55 49 0.1736 1.1150 127.5 5.6
2010 10 04 01 15 06.8 +56 17 23 0.1685 1.1108 127.4 5.5
2010 10 05 01 28 06.3 +56 34 04 0.1635 1.1067 127.2 5.4
2010 10 06 01 42 00.6 +56 44 50 0.1588 1.1028 127.0 5.4
2010 10 07 01 56 47.6 +56 48 35 0.1543 1.0990 126.8 5.3
2010 10 08 02 12 23.1 +56 44 09 0.1500 1.0954 126.6 5.2
2010 10 09 02 28 40.3 +56 30 20 0.1459 1.0920 126.4 5.1
2010 10 10 02 45 30.4 +56 06 03 0.1420 1.0887 126.2 5.0
2010 10 11 03 02 42.3 +55 30 16 0.1385 1.0855 125.9 4.9
2010 10 12 03 20 03.3 +54 42 12 0.1352 1.0826 125.7 4.8
2010 10 13 03 37 20.3 +53 41 20 0.1322 1.0798 125.4 4.8
2010 10 14 03 54 20.4 +52 27 27 0.1295 1.0771 125.0 4.7
2010 10 15 04 10 51.8 +51 00 41 0.1271 1.0747 124.6 4.6
2010 10 16 04 26 44.9 +49 21 35 0.1251 1.0724 124.2 4.6
2010 10 17 04 41 52.2 +47 30 59 0.1235 1.0702 123.7 4.5
2010 10 18 04 56 08.4 +45 30 03 0.1223 1.0683 123.2 4.5
2010 10 19 05 09 30.8 +43 20 09 0.1214 1.0665 122.6 4.5
2010 10 20 05 21 58.4 +41 02 54 0.1209 1.0649 122.0 4.5
2010 10 21 05 33 31.9 +38 39 56 0.1208 1.0635 121.4 4.4
2010 10 22 05 44 12.9 +36 12 59 0.1211 1.0623 120.7 4.4
2010 10 23 05 54 04.1 +33 43 43 0.1218 1.0612 120.0 4.4
2010 10 24 06 03 08.3 +31 13 42 0.1228 1.0604 119.3 4.5
2010 10 25 06 11 28.7 +28 44 22 0.1242 1.0597 118.7 4.5
2010 10 26 06 19 08.7 +26 16 58 0.1259 1.0592 118.0 4.5
2010 10 27 06 26 11.4 +23 52 34 0.1280 1.0588 117.3 4.5
2010 10 28 06 32 39.8 +21 32 02 0.1304 1.0587 116.7 4.6
2010 10 29 06 38 36.8 +19 16 02 0.1330 1.0587 116.1 4.6
2010 10 30 06 44 05.1 +17 05 04 0.1359 1.0590 115.6 4.7
2010 10 31 06 49 07.0 +14 59 27 0.1391 1.0594 115.1 4.7
-------------------------------------------------------------
2010 11 01 06 53 44.8 +12 59 24 0.1424 1.0600 114.6 4.8
2010 11 02 06 58 00.6 +11 04 58 0.1460 1.0607 114.2 4.8
2010 11 03 07 01 56.0 +09 16 10 0.1498 1.0617 113.9 4.9
2010 11 04 07 05 32.9 +07 32 55 0.1537 1.0628 113.6 5.0
2010 11 05 07 08 52.5 +05 55 03 0.1578 1.0641 113.4 5.0
2010 11 06 07 11 56.4 +04 22 26 0.1620 1.0656 113.2 5.1
2010 11 07 07 14 45.7 +02 54 49 0.1663 1.0673 113.1 5.2
2010 11 08 07 17 21.5 +01 32 01 0.1708 1.0692 113.0 5.2
2010 11 09 07 19 44.8 +00 13 47 0.1753 1.0712 112.9 5.3
2010 11 10 07 21 56.5 -01 00 06 0.1799 1.0734 112.9 5.4
2010 11 11 07 23 57.4 -02 09 52 0.1846 1.0758 113.0 5.5
2010 11 12 07 25 48.2 -03 15 46 0.1894 1.0783 113.1 5.5
2010 11 13 07 27 29.6 -04 17 59 0.1942 1.0810 113.2 5.6
2010 11 14 07 29 02.2 -05 16 44 0.1991 1.0839 113.3 5.7
2010 11 15 07 30 26.5 -06 12 13 0.2040 1.0870 113.5 5.8
2010 11 16 07 31 43.0 -07 04 36 0.2090 1.0902 113.8 5.9
2010 11 17 07 32 52.1 -07 54 05 0.2140 1.0935 114.0 5.9
2010 11 18 07 33 54.3 -08 40 49 0.2191 1.0971 114.3 6.0
2010 11 19 07 34 49.8 -09 24 56 0.2241 1.1007 114.6 6.1
2010 11 20 07 35 39.0 -10 06 36 0.2292 1.1046 114.9 6.2
2010 11 21 07 36 22.2 -10 45 55 0.2343 1.1086 115.3 6.2
2010 11 22 07 36 59.6 -11 23 01 0.2395 1.1127 115.7 6.3
2010 11 23 07 37 31.6 -11 58 00 0.2446 1.1170 116.1 6.4
2010 11 24 07 37 58.4 -12 30 59 0.2497 1.1214 116.5 6.5
2010 11 25 07 38 20.1 -13 02 03 0.2549 1.1260 117.0 6.6
2010 11 26 07 38 36.9 -13 31 17 0.2601 1.1307 117.4 6.6
2010 11 27 07 38 49.1 -13 58 45 0.2653 1.1355 117.9 6.7
2010 11 28 07 38 56.8 -14 24 31 0.2705 1.1405 118.4 6.8
2010 11 29 07 39 00.1 -14 48 40 0.2757 1.1456 118.9 6.9
2010 11 30 07 38 59.4 -15 11 15 0.2809 1.1509 119.5 7.0
-------------------------------------------------------------
2010 12 01 07 38 54.6 -15 32 19 0.2861 1.1562 120.0 7.0
2010 12 02 07 38 46.0 -15 51 54 0.2914 1.1617 120.6 7.1
2010 12 03 07 38 33.7 -16 10 04 0.2966 1.1673 121.2 7.2
2010 12 04 07 38 17.9 -16 26 51 0.3019 1.1730 121.7 7.3
2010 12 05 07 37 58.8 -16 42 17 0.3072 1.1789 122.3 7.4
2010 12 06 07 37 36.5 -16 56 24 0.3125 1.1848 123.0 7.4
2010 12 07 07 37 11.2 -17 09 14 0.3178 1.1908 123.6 7.5
2010 12 08 07 36 43.2 -17 20 50 0.3232 1.1970 124.2 7.6
2010 12 09 07 36 12.4 -17 31 13 0.3286 1.2033 124.8 7.7
2010 12 10 07 35 39.2 -17 40 26 0.3340 1.2096 125.5 7.8
2010 12 11 07 35 03.7 -17 48 29 0.3394 1.2161 126.1 7.9
2010 12 12 07 34 26.1 -17 55 25 0.3449 1.2226 126.8 7.9
2010 12 13 07 33 46.4 -18 01 15 0.3504 1.2293 127.4 8.0
2010 12 14 07 33 05.0 -18 06 01 0.3559 1.2360 128.1 8.1
2010 12 15 07 32 21.8 -18 09 45 0.3615 1.2428 128.7 8.2
2010 12 16 07 31 37.1 -18 12 28 0.3671 1.2498 129.4 8.3
2010 12 17 07 30 51.1 -18 14 11 0.3728 1.2567 130.0 8.3
2010 12 18 07 30 03.9 -18 14 56 0.3786 1.2638 130.7 8.4
2010 12 19 07 29 15.5 -18 14 45 0.3843 1.2710 131.3 8.5
2010 12 20 07 28 26.3 -18 13 38 0.3902 1.2782 132.0 8.6
2010 12 21 07 27 36.2 -18 11 38 0.3961 1.2855 132.6 8.7
2010 12 22 07 26 45.5 -18 08 46 0.4020 1.2929 133.3 8.8
2010 12 23 07 25 54.2 -18 05 03 0.4081 1.3003 133.9 8.8
2010 12 24 07 25 02.6 -18 00 30 0.4142 1.3078 134.5 8.9
2010 12 25 07 24 10.6 -17 55 10 0.4203 1.3154 135.1 9.0
2010 12 26 07 23 18.5 -17 49 02 0.4266 1.3230 135.7 9.1
2010 12 27 07 22 26.3 -17 42 09 0.4329 1.3307 136.3 9.2
2010 12 28 07 21 34.3 -17 34 32 0.4393 1.3384 136.9 9.2
2010 12 29 07 20 42.4 -17 26 13 0.4458 1.3462 137.5 9.3
2010 12 30 07 19 50.9 -17 17 11 0.4524 1.3541 138.1 9.4
2010 12 31 07 18 59.9 -17 07 30 0.4591 1.3620 138.6 9.5
-------------------------------------------------------------
Deep Impact
---------
Hartley-2 is only the second comet bright enough to be appreciated
by the public during a spacecraft visit. The other, the first, was
Halley in 1986. All other spacecraft-comet meets occurred when the
comet was too faint for easy view by the public. For this reason,
space advocates may show Hartley-2 in the sky as a visible example of
the space program, rather than relying only on media reports.
Deep Impact is the first spaceprobe to interact with a comet.
Prior visits were passive flybys to investigate the comet but not
disturb it. On 5 July 2005 it fired two darts into the nucleus of
9P/Tempel-1 to break out interior materials before solar heating
disturbs them. The hits were not visible from New York because their
timing was optimized for the West Coast and Hawaii, whose large
observatories were ready to see them.
After visiting 9P the spacecraft entered an extended mission to
inspect a second comet, 85P/Boethin. To reach Boethin the probe needed
a gravity assist from an Earth flyby in December 2007.
Boethin was due to return in 2008. By summer 2007 the comet didn't
show up. We either had a inaccurate orbit for it or it dissipated.
The alternative was 103P, returning in 2010. A change of course
began on 27 December 2007. The Earth swingby was tweaked to reach
Hartley-2. The mission would take 2 more years and 3 more Earth flybys
We will see, in a high dark sky from the City, the encounter on
November 4. Inspection of the comet begins on September 5 and ends on
November 25. Here's a timeline of Deep Impact
---------------------------------------------------------
2005 Jan 12 - Deep Impact launch toward comet 9P/Tempel-1
2005 Jul 4 - DI meets Tempel-1, fires darts into it
2006 Aug - DI heads for comet 85P/Boethin
2007 Oct - 103P/Hartley-2 alternate for 85P/Boethin
2007 Dec 27 - DI changes to head for 103P/Hartley-2
2007 Dec 31 - close flyby of Earth
2008 Dec 29 - close flyby of Earth
2009 Jun 19 - far flyby of Earth
2009 Dec 28 - far flyby of Earth
2010 Jun 27 - close flyby of Earth
2010 Sep 5 - DI begins examination of Hartley-2
2010 Oct 20 - Hartley-2 proximity to Earth
2010 Oct 28 - Hartley-2 perihelion
2010 Nov 4 - DI meets Hartley-2, ~1,000km
2010 Nov 25 - DI ends examination of Hartley-2
----------------------------------------------
As at mid September 2010 there are no announced ideas for sending
Deep Impact to a third comet.
For ordinary telescopes there is nothing special to see during the
Deep Impact flyby. With no more darts, there is no flare up or other
visible effect. The comet behaves as if nothing happened, altho Deep
Impact passes only 1,000 kilometers from it.
Deep Impact is one of many spacecraft visiting comets since the
first in 1986 to inspect comet 1P/Halley. Here is a table of comet
visits, plus a couple in the future.
----------------------------------------
1986-03-06 Vega 1 Flyby of Halley
1986-03-08 Suisei Flyby of Halley
1986-03-09 Vega 2 Flyby of Halley
1986-03-11 Sakigake Flyby of Halley
1986-03-14 Giotto Flyby of Halley
1992-07-10 Giotto Flyby of Grigg-Skjellerup
2001-09-22 Deep Space 1 Flyby of Borrelly
2004-01-02 Stardust Collect samples from Wild-2
2005-07-04 Deep Impact Shoot darts into Tempel-1
2006-07-06 Rosetta Fly thru Honda-Mrkos-Pajdusakova ion trail
2010-11-04 Deep Impact Flyby of Hartley-2
2011-02-15 Stardust Flyby of Tempel-1
2014-05-01 Rosetta Orbit & land at Churyumov-Gerasimenko
--------------------------------------------------------------
We had several failures, from a variety of causes, showing that
space projects are not fully reliable.
--------------------------------------------------------
1996-02-03 Sakigake Flyby of Honda-Mrkos-Pajdusakova
1998-11-29 Sakigake Flyby of Giacobini-Zinner
2001-01 Deep Space 1 Flyby of Wilson-Harrington
2003-11-12 Contour Flyby of Encke
2006-06-18 Contour Flyby of Schwassmann-Wachmann-3
2008-09 Deep Impact Flyby of Boethin
2008-08-16 Contour Flyby of d'Arrest
---------------------------------------------------
Of the comets visited, four were photographed: Halley, Borrelly,
Tempel-1, and Wild-2. The others were investigated without imaging.
Mutations by Jupiter
------------------
The returns of comet 103P/Hartley-2 illustrate the mutations of a
comet orbit due to close encounters with Jupiter. The signature of
mutation is the perihelion distance, the first field in each entry
under the title '103P'. This material is based on Kinoshita's 'Comet
orbit home page' website as at April 2010.
The frequent approaches to Jupiter are cause by the proximity of
the comet's aphelion and ascending node to Jupiter's orbit and low
orbit inclination. This proximity is the same feature that for Earth
could produce a meteor shower. We have no evidence for a Hartley-2
meteor shower on Jupiter.
Hartley-2 is tugged many times by Jupiter and a few by earth, the
latter with only minor modulations of the orbit. Such distortion of
comet orbits is common, specially in the Jupiter family of comets.
The fields in each entry are:
line 1: comet designation, comet name, asterisk 'not observed'
flag, perihelion date
line 2: perihelion distance in AU, excentricity, argument of
perihelion, longitude of ascending node, inclination, epoch of the
elements
line 3: when Hartley-2 comes close to Earth or Jupiter, a
third line gives the interacting planet, proximity AU, and
proximity date.
-----------------------------------------------------------
returns before discovery in 1986
--------------------------------
103P Hartley *1903-02-08.14559
2.0518993 0.5356198 142.94600 239.86645 17.09744 1903-02-15
103P Hartley *1912-06-01.52455
2.0622190 0.5347779 143.08194 239.87481 17.08717 1912-06-07
103P Hartley *1921-10-07.16386
2.0686155 0.5341476 143.12983 239.74981 17.08230 1921-09-28
103P Hartley *1931-02-04.86556
2.0574175 0.5345944 143.23591 239.66005 17.12103 1931-01-19
103P Hartley *1940-06-16.46622
2.0891874 0.5313073 144.89324 238.24948 17.21247 1940-06-20
Jupiter 0.2246 AU 1947-08-24.8 TT
103P Hartley *1949-09-26.00171
1.6216229 0.5920478 156.27642 236.83803 16.76859 1949-10-11
103P Hartley *1957-09-08.82061
1.6297883 0.5910685 156.50972 236.69901 16.78519 1957-08-30
103P Hartley *1965-08-15.99927
1.6193803 0.5924260 156.55832 236.67109 16.82276 1965-08-28
Jupiter 0.0851 1971-04-28.8
103P Hartley *1973-05-02.85939
0.9046493 0.7295589 177.02542 228.52974 8.09034 1973-04-28
103P Hartley *1979-06-17.66336
0.9042286 0.7296553 177.11056 228.46338 8.09559 1979-06-16 564
Jupiter 0.3255 1982-11-02.5
-------------------------------
returns since discovery in 1986
-------------------------------
103P/1986 E2 Hartley 1985-06-04.86939
0.9516158 0.7198380 174.81100 226.85391 9.25270 1985-06-24
103P/1991 N1 Hartley 1991-09-11.65165
0.9532959 0.7194930 174.89578 226.78441 9.25173 1991-09-21
Jupiter 0.3743 1993-12-19.3
103P Hartley 1997-12-22.01729
1.0317242 0.7003778 180.72265 219.95392 13.61882 1997-12-18
103P Hartley 2004-05-17.93900
1.0362737 0.6995086 180.80972 219.89811 13.60199 2004-06-04
Earth 0.1209 2010-10-20.8
-------------------------
future returns after 2010
-------------------------
103P Hartley 2010-10-28.26195
1.0586893 0.6951224 181.20103 219.76004 13.61839 2010-10-11
103P Hartley *2017-04-20.51927
1.0659932 0.6934488 181.30112 219.72447 13.59396 20170507 508
Earth 0.3818 2023-09-26.3
103P Hartley *2023-10-12.57652
1.0641023 0.6938314 181.30175 219.74995 13.61083 2023-1-023
103P Hartley *2030-04-05.61146
1.0680647 0.6930279 181.29831 219.76408 13.59155 2030-04-09
Earth 0.6269 2036 09 08.5
103P Hartley *2036-09-27.23614
1.0618407 0.6941552 181.31811 219.76029 13.61944 2036-09-24
103P Hartley *2043-03-12.51752
1.0525249 0.6960063 181.38891 219.76661 13.64157 2043-03-12
103P Hartley *2049-08-19.41102
1.0483750 0.6967196 181.45336 219.71798 13.66054 2049-08-27
Jupiter 0.7164 2054-03-19.0
103P Hartley *2056-01-04.82834
0.9618776 0.7148464 184.00262 218.26999 13.18802 2056-01-03
103P Hartley *2062-03-18.25970
0.9601372 0.7151760 184.08798 218.21109 13.19806 2062-04-01
Jupiter 0.2678 2065-11-13.8
103P Hartley *2068-03-25.67604
0.9441748 0.7223482 188.75543 209.91109 8.81133 2068-04-09
103P Hartley *2074-07-06.78067
0.9435124 0.7225629 188.87141 209.84278 8.81939 2074-07-07
Jupiter 0.2461 2076-12-11.3
103P Hartley *2080-06-21.88718
0.9229968 0.7247793 186.57593 207.98225 12.89865 2080-06-05
103P Hartley *2086-08-16.95372
0.9248434 0.7244692 186.65824 207.92204 12.89153 2086-09-02
Jupiter 0.4745 2088-07-29.3
103P Hartley *2093-01-12.48561
1.0536232 0.6966945 189.93239 206.23491 14.26999 2093-01-08
103P Hartley *2099-07-10.25193
1.0588402 0.6958038 190.00052 206.17864 14.24725 2099-06-26
103P Hartley *2106-01-12.46297
1.0679765 0.6939909 190.13259 206.17941 14.22766 2106-01-21
------------------------------------------------------------
Jupiter comets
------------
In the course of solar system history Jupiter collected a stable of
comets, the Jupiter family of comets. These are thought to be captured
from the Kuiper Belt and perhaps contain primitive material with no
disturbance by planet-forming processes.
This prospect alone made Jupiter comets prime candidates for
spacecraft visits. Other factors are small ecliptic inclination, to
avoid plane-change maneuver by the spacecraft, and periods of only a
few years, for better chance that a suitable target is near to hand.
Jupiter comets lie close to the ecliptic, inclinations generally
less than 20 degrees and aphelion near Jupiter's orbit, 5 to 6 AU from
Sun. Additionally, many have one of their orbit nodes near aphelion,
to further increase the chance to get close to the very planet.
The good chance of a proximity to Jupiter every several laps of
the comet subjects the comet orbit to gravity distortion from the
planet. The orbit suffers change near aphelion to bend it on different
trajectories into the inner solar system. The reverse can happen, too,
where a comet is moved to a farther orbit, no longer easily observed.
That's how Hartley-2 was first noticed. Prior to 1980 it was in an
orbit too far away for detection, minding that before the 1980s we had
nothing like the instruments and information processing of today.
It so happens that the perihelia of many Jupiter comets are near 1
AU! It can be upsetting to think that these comets, could whump Earth
merely because Jupiter pulled them into our path around the the Sun.
What if Hartley-2's perihelion was shifted to quite 1 Au and not 1.06
for the 2010 return?
We would probably not be hit, but 103P would be a really close
object, among the very closest of all comets. How brilliantly it may
shine in our sky! On the other hand, the proximity to Earth makes for
a shorter, simpler, cheaper space mission to visit the comet.
Hartley-2 is sometimes called a young comet. We do not know when
it was formed, so this is not a chronological dating. The term refers
to the high level of activity during each apparition since discovery.
It seems to have a full charge of volatile gases with so far no sign
of running low. This may be because its prior orbit was too far from
the Sun to vaporize and thus lose the gases so vigorously.
103P starts jivving up after it rounds aphelion and starts falling
toward the Sun, as do most other comets. Its outgas continues thru
perihelion and into the outward arm of its orbit.
A feature for Hartley-2 and many other Jupiter comets is the
extended span of activity. After starting up on the inward arm of the
orbit, it continues to and beyond the next aphelion. There is only a
brief span when the comet is quiet before the next cycle of outgas
The nucleus of 103P seems to be rather small, only 1-1/2 kilometer
diameter. Other Jupiter comets we examined by spaceprobe have nuclei
of many to about 10 kilometer diameter. The inspection of the Hartley-
2 nucleus by Deep Impact will surely elucidate its true character.
The nucleus also may be tidally loosened during close approaxhes to
Jupiter, releasing interior dust. The dust trailsd the comet in its
orbit, as already spotted for hartley-2 in infrared observations. The
dust trail MAY cause a meteor shower when Earth is closest to the comet
or crosses its line of nodes.More on this in 'Meteor shower?'
Jupiter comets traditionally have distinct apparitions. They are
first spotted sometime after a given aphelion and are last seen
sometime before the next aphelion. Around aphelion they are invisible
because they are inactive and dim and the observing limitations
prevailing for each apparition.
Increasing so in recent years it is possible to observe a Jupiter
comet thruout its orbits all the way thru aphelion. There is no
recovery in the traditional sense to mark the start of a new
apparition.
The comet is then called a perennial comet, one that can, in
principle, be viewed at any time. Hartley-2 so far still has separate
apparitions but maybe this round will be the last one. We recovered
103P only a year after the last aphelion and probably can follow it
thru the next aphelion. If so, Hartley-2 joins the small but growing
ranks of perennial comets.
Resonance orbits
--------------
I'll discuss a bit about the effect of resonance between Jupiter
and Hartley-2, as an example of a common feature of Jupiter comets.
I give here only an illustration, assuming the comet's orbit is stable
after the meet of 1993. It isn't, as seen in the elements in the
'Apparitions' section.
Jupiter's period is 11.86 years; Hartley-2, 6.47. Start with the
comet and Jupiter were together at the comet's aphelion in 1993, we
first find the synodic period of comet as seen from Jupiter, from the
usual formula:
(syn per) = ((per home)*(per other))/((per home)-(per other))
'Home' is the planet we view from, Jupiter. 'Other' is, uh, the other
planet we are looking at.
(syn per) = ((11.86)*(6.47))/((11.86+)-(6.47))
= (76.73)/(5.39)
= (14.24)
Wholly unlike the synodic period of two planets, in thier nearly
circular orbits, the synodic period of 103P relative to Jupiter is
highly varaible. The aspect in Jupiter's sky is also quite varied due
to the wide range of distance the comet stands from Jupiter. The value
found here is only an average.
If we next ask when the two orbs are together at the comet's
aphelion, we must hop around Jupiter's orbit synodic period by synodic
period. This is found by the ratio of the two periods
(next meet at same orbital point) = (11.86)/(6.47)
= 1.833
This must be proportioned to a whole number of revolutions of both
Jupiter and comet. A few trials yield
(next meet at same orbital point) = (11.86/Jup lap)/(6.47/comet lap)
= (11/Jup lap)/(6/comet lap)
= (11 somet lap)/(6 Jupiter lap)
6 Jupiter laps around the Sun equals 11 laps of 103P. This brings
both bodies back to their mutual starting place, the aphelion of 103P
6 Jupiter years is (6)*(11.86) = 71.18 years. 11 comet years is
(11)*(6.47) = 71.18 years.
The next time we get a close meet of the two bodies is 71+ years
after 1993, in 2064. This IS off of the true next encounter in 2054
because I used a rigid comet orbit. The concept is valid that after
so many rounds of the comet and Jupiter the two again jive together.
At this second encounter the comet sswerves into a new orbit and
the prior resonance is broken; It is replaced by one based on the new
orbital parameters. Jupiter marches on his way completely unaffected.
Activity
------
Comets shine by sunlight reflecting from its nucleus and by self-
luminance from its coma. The coma material is transparent, so there is
little additional reflection from it in spite of its humongous size
compared to the nucleus.
A major study of comet luminance is under way by Ferrin, which
should be studied by comet fans. He has several pieces on his website
'webdelprofesor.ula.ve/ciencias//ferrin' including a special one on
103P issued in August 2010 and an atlas for many comets (except 103P).
Hartley-2 when far from the Sun has its volatile gases frozen on
its nucleus and the luminance is like that of an asteroid. The main
difference is that the nucleus may be shinier from ices on its
surface, not dark rock. The brightness by reflection is a simple rise
and fall entered and symmetrical on the time of perihelion.
At some distance from the Sun on the approach arm of the orbit,
solar heating is sufficient to sublime the ices and 103P turns on. It
flourishes from then, thru perihelion. On the reproach arm solar
hearing declines and the gases wane n light output. In the case of
103P there is still luminous activity from the coma thru aphelion and
into the next round of the comet. Condensation back to ices occurs
near the beginning of the next approach run and the comet turns off.
This process repeats for each visit. At each visit some material is
lost in the coma and tail, leaving less for future returns. Eventually
the comet runs out of volatile material and becomes an asteroid. We
suspect certain asteroids in cometary orbits are exhausted comets.
The light curve, plot of stellar magnitude against time, shows the
stages of light output counting from aphelion. The letters key to the
light curve below.
(a) When 103P is frozen there is a slow ramp up in brightness as
the comet approaches the Sun and reflects more sunlight from its
nucleus.
(b) At the turnon point there is an sudden contribution from
vaporization of the ices. The luminous output increases toward
perihelion as more gases are released and are more strongly heated by
proximity to the Sun.
(c) Te comet grows in brightness along a slope governed by the
kind and amount of gases producing the light. This is when most home
astronomers first notice the comet.
(d) 103P has a break in the slope of the light curve shortly
before perihelion. Hartley-2 has two main types of volatiles, the CO2
and H2O class. The CO2 gases, including CO2 itself sublime first,
while the H20, with real water, are harder to vaporize. The comet
turns on with its CO2 vapors and later ignites its H2O vapors.
(e) The peak brightness is a little later than perihelion, not
right at it. This lag of peak brightness is due to the heat budget of
the comet similar to why our summer is hottest after the solstice,
rather than right around it.
(f) As solar heating declines on the outward run of the comet, the
gases contract and their contribution to brightness wanes. Now both
kinds of gases are well mixed in the coma with no segregation of H2O
and CO2. There is no break in slope after perihelion.
(g) By aphelion there is still vaporized gas lingering on 103P
adding light above the pure nucleus reflection. This activity
persisting after aphelion is the spillover effect, seen also in
certain other comets.
(h) The gases are finally frozen at the turnoff point. The comet
shines by reflection from the nucleus while riding inward toward the
next turnon point.
In ASCII, the normal light curve is:
perihelion peak brightness
| |
| /\
H2O turn on | / e \
| / \
| / | \
/d | \
/ | \ f
CO2 turn on / c | \
| / | \
aphelion turn off |/ | \ aphelion
| | / b | \ |
|\ g | / a | |g
| \ |/ | |
+-----h--------------------+--------------------------+
before | after
Home astronomers typicly see a comet for the first time while it
is active. We recognize a comet partly by its coma, which is a lot
more obvious than a nucleus. The nucleus looks just like an asteroid.
No one hunts for asteroids visually any more, but we still search for
comets by eye at the telescope.
Magnitude estimates of the comet when active are made primarily by
home astronomers while our campus colleagues engage in studies by more
sophisticated instruments. Campus astronomers can do the studies when
the comet is inactive, so most nucleus information comes from them.
The light curve of Hartley-2 can be stacked from each apparition
to build a composite, much like we do for variable stars or exoplanet
transits. The curve starts at the the previous aphelion and ends at
the next one.
With the stacked, or folded or composite, light curve the plotted
magnitudes can NOT be those expected for a given apparition. The
plots, due to the radicly different observing conditions for each
visit, are normalized in a way that's tough to visualize. A 'real'
magnitude can be calculated from the curve but not by an easy in-the-
head method.
The study of Hartley-2 is complicated by the changing orbit and
paucity of observations in 1985 and 2004. The best data prior to this
2010 return was from the 1997 return. Already we are gathering far
more and better data in the current round than ever before.
So far they seem to agree with previous information and fit well
into the comet's light curve.
Here is a timetable, based on Ferrin's work, of significant events
for comet 103P/Hartley-2:
---------------------------------------------------------------
distance | time | event
---------+---------+------
5.86 AU | -1167 d | previous aphelion
5.4 AU | -830 d | turn off & spillover from previous lap
4.2 AU | -400 d | turn on for CO2
1.2 AU | -41 d | turn on for H2O
1.07 AU | -10 d | proximity to Earth
1.06 AU | 0 d | perihelion, 2010 Oct 28
1.06 AU | +7 d | meet with Deep Impact
1.08 AU | +16 d | peak brightness
5.86 AU | +1167 d | next aphelion
5.4 AU | +1504 d | turn off & spillover to next lap
---------+---------+----------------------------------
Observing the comet
-----------------
Treat 103P like any other deep sky target in the fall and winter
sky. If you're rusty in this type of observing, please practice with
targets plausibly similar to Hartley-2. These include M2 in Aquarius,
M15 in Pegasus, M31 in Andromeda, M34 in Perseus.
Believe it or not, I personally, with Top of the lawn crew, got a
pleasing view of M15 FROM CENTRAL PARK ON MANHATTAN on 14 September
2010! We used a 100mm refractor near the floodlights of Wollman
skating pond. Many authors, some respectable, claim there is little
hope of stargazing -- or, so wrongly!, astronomy -- from New York. We
can and we do.
Hartley-2 flies along the Milky Way for much of its path. You
better walk along the Milky Way with binoculars to acquaint with
wayside features that can fool you. Tiny clumps of stars, enhanced
patches, globular nebular, all can be mistaken for the comet by an
inexperienced observer. Recall that Messier himself got so fed up with
being tricked that he started to compile his catalog of nebulae and
clusters. That was in the mid 18th century.
One point to remember is that most timetables and ephemerides of
comets are calcked for 0h UT on the listed date. Read the accompanying
text carefully. This means that the entry is for 20h EDST on the
PREVIOUS calendar date, or 19h EST starting in November.
For 103P this is particularly lucky because the 19-20 hour span is
exacta mente when the comet is in high sky. You look in the spot
marked for the NEXT calendar day in the ephemeris.
DOn't expect much of a tail. Some finder charts show a long brushy
tail. This is either just a stylized symbol or a schematic tail of a
nominal linear length. The program plots the angular length and
orientation of a tail of, say, 15 million kilometer (1/10 AU).
If so, you may assess your own view by comparing it to the
standard one. Your view may reveal 3 degrees of tail. The chart has
one of 13 degree. The linear length you see is a direct proportion:
(your length) = (3/13)*(15 million km) = 3.46 million km.
Photography of the comet is like that of deepsky objects. If you
can successfully image other autumn targets, you'll capture Hartley-2.
The exposure duration may be curtailed by the rapid proper motion of
103P as the only main caution.
Meteor shower?
------------
in 1997 Jennisken called attention to a possible meteor shower
from Hartley-2 during its visit in that year. He figured out a radiant
near beta Cygni with a spurt of meteors lasting a couple hours. He
gave a range of 2-4 November 1997 to watch for the shower but no
shower was definitely reported.
The 2010 visit puts Earth near Hartley-2 when it is rounding
perihelion. Altho we are still some 18 million kilometers from the
comet at proximity, its dust trail could reach out and send shooting
stars to us.
Computing a meteor shower radiant is an exercise in 3D geometry
and vectors. Because the calcs are rarely set out in the usual
litterature, I give here my own figures.
By good fortune, 103P and Earth are running about parallel during
proximity and perihelion. Both occur near the comet's descending node,
so the radiant should be north of th ecliptic.
This simplifies the angle between Earth and comet speed vectors,
relative to Sun, to be essentially the orbit inclination. This for
103P is 13.6 degree in a prograde orbit.
A curious fact is that at 1AU, where a meteor shower must take
place on Earth, the speed of a comet relative to the Sun is 42 km/s.
This is amazingly stable almost no matter what the orbital motion is,
so in lack of an actual value, you may use this to start. I checked
this for Hartley-2 with the JPL HORIZONS and it is in fact 42 km/s
(rounded). We have the vector triangle:
\\
\ \
\ \ V(c/s)
\ \
V(c/e) \ \
\ \
A ---------------------- 13.6d
V(e/s)
By the law od Cosines, we get
V(c/e)^2 = (V(c/s))^2+(V(e/s))^2-(2)*(V(c/s))*(V(e/s))*cos(incl)
= (42km/s)^2 + (30km/s)^2 - (2)*(42)*(30)*cos)13.6)
= (1764)+(900)-(2520(*(0.9720)
= (214.66)
v(C/E) = 14.65km/s
The meteors are chasing after Earth from behind it.
We need the angle of the meteors, of V(c/e) to get the ecliptic
latitude. This is the angle A in the diagram above. The exterior angle
is the proper one. This is gotten by the Law of Sines:
sin(A) = sin(incl) * (V(c/s)) / (V(c/e))
= sin(13.6) *(42km/s) / (14.65km/s)
= (0.2351) * (2.867)
= (0.0.6741)
A = 42.38 degree
At the time of proximity, 2010 October 20, when the chance of
catching shooting stars may be greatest, the Sun is in ecliptic
longitude 206 degree, by correlation of longitude and calendar date.
Recall that Earth is heading in her orbit into a point on the
ecliptic 90 degree BEHIND the Sun, into in this case longitude 116
degrees, about half between Alhena and Pollux.
The meteors are catching up to Earth from behind, 180 degrees from
Earth's motion, a chance simplification due to the parallel paths of
Earth and comet. In the general case we have to measure the angle of
attack of the comet orbit on Earth's. This is probably easiest done by
scaling from an orbit plot in a computer solar system program.
One error, a really common one, is to look DOWN the path of the
comet and not UP, into where the meteors are coming FROM. The radiant
is the UPRANGE vanishing point along the comet orbit, not the
downrange one. The wrong choice sends you to the diametricly opposite
point in the sky.
The shooting stars emanate from longitude 296 degree. Therefore,
the radiant, by my approximate work, is at ecliptic lat = +42d, lon =
296d. By the coordinate conversion feature of a computer starchart
program, this point is at RA = 19h 21m, dec = +20d. Spotting this
point on the starchart yields a location a couple degree west of the
Coathanger, Brocchi's, Al Sufi's, Collinder 399, star cluster!
We may look for meteor activity -- if there is any! -- at
----------------------------------
RADIANT OF HARTLEY-2 METEOR SHOWER
AT EARTH'S PROXIMITY TO COMET
-----------------------------
ecliptic: lon = 296d, lat = +42d
equator: RA = 19h 21m, dec + +20d
sky point: couple degree west of Coathanger cluster
date: a few days centered on 2010 October 20
--------------------------------------------
An other time to be on guard for a meteor shower is the moment of
nodal crossing. 103P's line of nodes sits 219.8d toward the ascending
node, near Jupiter, to 39.8d toward the descending node, near Earth.
Earth crosses the descending side on 2 November 2010, taken from a
date-longitude conversion.
The radiant, happily, is shifted almost entirely in ecliptic
longitude, with only 2 degrees of southward shift in latitude. The
longitude shift is 12 degrees, This is the 12 days farther motion of
Earth in her orbit since the proximity date of 20 October. The radiant
for the nodal date is:
----------------------------------
RADIANT OF HARTLEY-2 METEOR SHOWER
AT EARTH'S NODAL CROSSING
-------------------------
ecliptic: lon = 308d, lat = +40d
equator: RA = 20h 01m, dec = +20d 28m
sky point: 8d east of Coathanger Cluster
date: a few days centered on 2010 November 2
--------------------------------------------
These radiants, like other radiants, drift eastward quite 1 degree
of longitude per day. The meteors will come from points EAST for later
dates and WEST for earlier ones. Since a radiant is not a true point,
but a spot a few degree diameter, as long as you're observing in late
October-early November, look at the Coathanger.
This area is in the EVENING sky, not the typical morning sky for
meteor showers. There is NO guarantee of any shooting stars, but
meteor fans can enjoy a cool autumn evening watching for them.
'Enjoy' is putting things politely. To stage a vigil for possible
Hartley-2 meteors you need a darksky viewing site, just like for other
meteor showers. Under a luminous sky you may see nothing resembling a
shower. The thinking is that there may be only a splash of shooting
stars for a couple hours on ONE of the days centered on the proximity
of October 20th.
Patience, endurance, stoicism are prime prerequisites for catching
any Hartley-2 meteors. Also hold in mind the recognition that there is
NO prior history of shooting stars from this comet.
Conclusion
--------
The 2010 return of 103P is by far the most favorable of all since
discovery. It occurs in the fall season in the City, when the sk is
generally the clearest and darkest. It happens within the annual
Milky Way season during which there is the best chance of spotting the
brighter patches of the Milky way from within the City frontiers., It
opens on September 1 and runs thru November 30.
The main celestial impediment is the Moon. When she is near the
comet, in Aquarius thru Gemini, her light may wash out the comet just
as she does to deepsky objects. Note that she is then in large phase,
being roughly opposite the Sun in the local sky.
Space fans are going wild with Hartley-2 as a shining specimen to
for the space program. They can point to the comet and explain about
Deep Impact and other interplanetary probes. Not since Halley in 1986
could they do this so conveniently for the public.
As an astrodynamical specimen 103P will thrill you. Crank up your
dynamics model of the solar system and watch Jupiter shift Hartley-2's
orbit this way and than over the decades.
It's been a while ago that we in New York had a good comet. Most
others were dim and diffuse, The lst really good one was Hale-Bopp in
1997 and the surprise treat of the explosion in Holmes in 2007. We are
ITCHING to see a bright comet and here it is!