IRIS is the seventh known asteroid to be discovered, and was by J.R. Hind from Regent’s Park in London on 13th August 1847 being found in the same year as the asteroids 6 Hebe and 8 Flora. John Hind found Iris during a dedicated systematic search program that had started in November 1846, just two months after the new discovery of the outer planet, Neptune. At 8.9 magnitude, Iris was remarkably similar to Neptune but showed no real discernible disk. Such planetary searches had come into vogue in the 1840s and 1850s, with many visual astronomers during this time in the hope of some new discovery of their own. In the following months Hind measured Iris position every clear night that he could.
IRIS DATADiscoverer : J.R. Hind Date : 12th August 1847 Satellites : 0 Diameter : 225×190×190 km. Polar Tilt : 85° Period (P) : 3.68 years Synodic Period : 463.1 days Orbital Velocity : 19.0 km.s-1 Perihelion (q) : 1.833 A.U. Aphelion (Q) : 2.937 A.U. Eccentricity (e) : 0.231 Inclination (i) : 5.53° Mass : 1.26×1019 kg. Mean Density : 2.9 g.cm-3 Mean Distance : 2.385 AU or 3.568×108 km. Sidereal Rotation : 7.14 hr. Mean Sidereal Rotation : 0.2975 d. Maximum Diameter : 0.32″ (arcsec) Minimum Diameter : 0.06″ (arcsec) Maximum Magnitude : 6.7 Minimum Magnitude : 11.4 |
Timing of the discovery was also fortuitous, as in the same field the comparison star of 6.5 magnitude 65 Sgr, This was also used to determine the brightness and changing asteroidal positions. In addition, the Sicilian observer, G. Piazzi, used 5.7 magnitude 63 Sgr between 19th, 20th and 24th August. These observations together quickly confirmed Iris was another main asteroid belt object lying between the orbits of Mars and Jupiter.
I mention Iris here, mainly because Charles Rümker, then at the Hamburg Observatory, he made several positional observations using transit and meridian telescopes for the asteroid. His first observation was made on 20th August, remarkably conveyed to him within six days of the announcement of the discovery - made even more amazing by the lack of any modern-day communications! Rümker observed Iris twenty times between 20th August and 19th September 1847.
After five separate observers observations were collected and collated, Professor Challis of Cambridge produced the orbital elements of Iris by the end of the month, which were followed by the elements of the noted observers of A. Graham, Prof. Encke, J. Hind and M. d'Arrest. The discovery and various calculated orbits were all published together in the September Monthly Notices of the Royal Astronomical Society (MNRAS.); MNRAS., 7, 17, p.299-302 (1847) one after the other. Also, the first ephemeris of Iris was issued by d’Arrest, from his own calculated elements, which appears in MNRAS, 8, 1, pg.5 (1847).
It should also be noted that this same MNRAS of 1847 also has the elements of the sixth asteroid found, Hebe. pg. 303-305. This is followed pg.305 Rümker’s twenty positional meridian observations of Neptune, along with several others observers, which was also used to determine Neptune’s orbit with far better precision. [Also Lassell’s notification about Neptune in a letter to the RAS appears on pg. 297-298, just prior to Iris own announcement to them.]
COMMENT: What is really remarkable here was the huge step forward in matching visual observation, measurement of positions by several different observatories, and using the results to calculate the asteroid orbit. Such co-operation was fairly new occurrence in astronomical circles, as much of the earlier discoveries were made for “king and country” - mainly to placate their funding masters. This was to auger the new spirit of international efforts in astronomical observations - a trend that continues today. Although Hebe was found before Iris, the first in the MNRAS publication was the brighter Iris. As such, in my opinion, the discovery marks a corner stone in the way planetary bodies are discovered and then have their orbits and general natures quickly determined.
Although smaller than the other main minor planets, Iris has a high surface brightness, and hence at close oppositions can rise just below the naked-eye limit at +6.7 magnitude - also last achie\ive recently on 18th November 2006. Andrew Hollis J.BAA., claims there have been several visual sightings of Iris, and if true, this must be one of the faintest solar system objects possibly to be seen.
There has been renewed interest in observing Iris, which is catalogued as on S-type asteroid, being the brightest and probably the largest of this group. Photometrically, this object has been well and frequently studied by observers. The rotational period has been determined as 7.139 hours (0.2976 days), an amplitude range between 0.04 and 0.29 magnitudes. These variations were earlier discovered by Prof. Wendell on 25th January 1904, being estimated to be about 0.259 days from the average fluctuation in brightness of 0.2 magnitudes, which can change at times by as much as 0.09 to 0.35. A slightly revision from Wendall’s data as made in 1922 by Harvard Observatory.
Some of these results have been also been recently determined and confirmed by U.K. amateur astronomers (Hollis 2001) of the British Astronomical Association (B.A.A.) from instrumental observations during oppositions in 1989 and 1991. Other photoelectric observations of Iris have confirmed that the surface of Iris is likely covered by different regions of several bright and dark areas, which are suspected to be caused by meteor impacts or even possibly mountain-like structures as the asteroid rotates. Hoffman and Geyer (1993) have concluded that Iris might show significant “…large bright region in the northern hemisphere”. Similar observations have been made with Vesta, which have been confirmed by radar in 1994 and by visual observations by the Hubble Telescope. Similar results have been seen with (8) Flora.
The orbit was also recently revised by the Polish observer I. Wlodarczyk (1993).
Iris is the Greek goddess of the rainbow, and was the daughter of Typhon and Echidna. Iris is married to Zephyrus (west wind), and has a son named Phineas. She was the goddess who ran errands for the main Greek god, Hera, and sometimes even for Zeus. She was usually acting as the main go-between mortal humans and the gods, passing on her flying the messages and errands - very much like angels. Her golden wings descended from Olympus on the arc of the rainbow - thus seemingly joining the earth and sky. Iris does similar thing to Mercury, and carries the caduceus - a staff with wings wrapped by two intertwining snakes - often used to represent doctors and medicines. Sometimes she carries a pitcher of water, which supplies the clouds with rain. This sometimes makes Iris joyful display a rainbow that is helped to be lit by the rays of the sun from Helios / Helius. Iris can also use water obtained from the underworld river Styx and put mortals to sleep.
Her two other sisters, named Aellopus and Ocypete, also known as the Harpies, which were winged female evil creatures akin to dark angels. Considered dangerous and wicked, who inflicted on their victims displays of violent, cruel and vindictive behaviours. Iris avoided this awful fate. In mythology, she was associated with the flying Boreads (North Wind), who interestingly relates to the other colourful goddess, Aurora. Iris instructed him to finally illuminate them, as they were bothering her son, Phineas, and who were abhorrent to humankind. He killed one of the Harpes, and then ostracising the other from Thrace.
*********************************************************
0h UT (J2000) Mag Δ r El. Con
DATE R.A. Decl. V A.U. A.U. o
hh mm.m o ′
*********************************************************
12 Jan 13 20.9 -14 37 10.8 2.595 2.725 087 Vir
26 Jan 13 29.4 -15 51 10.7 2.422 2.749 099 Vir
09 Feb 13 33.8 -16 43 10.5 2.254 2.772 111 Vir
23 Feb 13 33.5 -17 07 10.3 2.101 2.793 125 Vir
08 Mar 13 28.1 -16 59 10.0 1.976 2.813 140 Vir
22 Mar 13 18.2 -16 15 09.7 1.891 2.832 156 Vir
05 Apr 13 05.6 -15 00 09.5 1.857 2.849 171 Vir
19 Apr 12 52.8 -13 27 09.6 1.879 2.864 166 Crv
03 May 12 42.4 -11 53 09.9 1.956 2.879 151 Crv
17 May 12 36.0 -10 35 10.2 2.079 2.891 136 Vir
31 May 12 34.2 -09 44 10.5 2.238 2.902 122 Vir
14 Jun 12 36.8 -09 22 10.7 2.420 2.912 109 Vir
28 Jun 12 43.2 -09 27 10.9 2.615 2.920 097 Vir
12 Jul 12 52.7 -09 56 11.1 2.814 2.926 086 Vir
26 Jul 13 04.9 -10 44 11.2 3.009 2.931 076 Vir
09 Aug 13 19.2 -11 46 11.3 3.195 2.935 066 Vir
23 Aug 13 35.2 -12 59 11.4 3.367 2.936 057 Vir
06 Sep 13 52.7 -14 18 11.4 3.520 2.937 048 Vir
20 Sep 14 11.5 -15 42 11.4 3.650 2.935 039 Vir
04 Oct 14 31.3 -17 06 11.4 3.756 2.933 030 Lib
18 Oct 14 52.1 -18 27 11.3 3.834 2.928 021 Lib
01 Nov 15 13.7 -19 44 11.2 3.883 2.922 013 Lib
15 Nov 15 36.0 -20 54 11.0 3.900 2.915 004 Lib
29 Nov 15 58.9 -21 55 11.0 3.887 2.906 005 Sco
13 Dec 16 22.0 -22 45 11.1 3.842 2.895 014 Sco
27 Dec 16 45.2 -23 23 11.2 3.766 2.883 023 Oph
*********************************************************
Iris is certainly fairly disappointing for observers during 2008. Opposition will be reached on 6th April in southern Virgo, when the magnitude rises to 9.5. At the beginning of the year, Iris is well placed for southern observers, and can be seen about midnight. However, it will be around mid-March when Iris will be visible in binoculars. During mid-April, this minor planet crosses for several weeks into the non-zodical constellation of Corvus before returning back into Virgo. After early July, Iris will drop below 11th magnitude, reaching in mid-September minimum magnitude of 11.4 — at the elongation of 44° — which is well before conjunction. Iris will continue its approach to solar conjunction on 23rd November. It will be best observed again after mid-March 2009.
*********************************************************
0h UT (J2000) Mag Δ r El. Con
DATE R.A. Decl. V A.U. A.U. o
hh mm.m o ′
*********************************************************
10 Jan 17 08.3 -23 48 11.3 3.661 2.869 032 Oph
24 Jan 17 30.9 -24 00 11.3 3.528 2.854 041 Oph
07 Feb 17 52.7 -23 58 11.3 3.371 2.838 050 Sgr
21 Feb 18 13.4 -23 45 11.2 3.193 2.820 059 Sgr
07 Mar 18 32.4 -23 22 11.1 2.998 2.800 069 Sgr
21 Mar 18 49.4 -22 51 11.0 2.791 2.779 079 Sgr
04 Apr 19 03.8 -22 14 10.8 2.578 2.757 089 Sgr
18 Apr 19 14.9 -21 35 10.6 2.364 2.733 101 Sgr
02 May 19 22.1 -20 57 10.4 2.157 2.708 112 Sgr
16 May 19 24.5 -20 24 10.1 1.966 2.681 125 Sgr
30 May 19 21.5 -19 58 09.7 1.800 2.654 139 Sgr
13 Jun 19 13.1 -19 39 09.4 1.671 2.625 155 Sgr
27 Jun 19 00.2 -19 26 08.9 1.586 2.594 171 Sgr
11 Jul 18 45.1 -19 17 08.9 1.554 2.563 171 Sgr
25 Jul 18 31.2 -19 08 09.2 1.574 2.531 155 Sgr
08 Aug 18 21.2 -19 02 09.4 1.639 2.498 139 Sgr
22 Aug 18 16.9 -18 59 09.7 1.740 2.464 125 Sgr
05 Sep 18 18.8 -18 58 09.9 1.865 2.429 112 Sgr
19 Sep 18 26.3 -18 57 10.1 2.002 2.393 100 Sgr
03 Oct 18 38.7 -18 51 10.2 2.144 2.357 089 Sgr
17 Oct 18 55.2 -18 36 10.3 2.284 2.320 080 Sgr
31 Oct 19 15.0 -18 08 10.4 2.417 2.283 070 Sgr
14 Nov 19 37.5 -17 25 10.4 2.539 2.246 062 Sgr
28 Nov 20 02.0 -16 22 10.4 2.648 2.209 054 Sgr
12 Dec 20 28.0 -15 00 10.4 2.741 2.173 046 Cap
26 Dec 20 55.3 -13 17 10.3 2.817 2.137 038 Aqr
*********************************************************
*********************************************************
0h UT (J2000) Mag Δ r El. Con
DATE R.A. Decl. V A.U. A.U. o
hh mm.m o ′
*********************************************************
09 Jan 21 23.4 -11 13 10.2 2.877 2.101 031 Aqr
23 Jan 21 52.1 -08 51 10.1 2.919 2.067 025 Cap
06 Feb 22 21.3 -06 11 10.0 2.946 2.034 018 Aqr
20 Feb 22 51.0 -03 16 09.8 2.957 2.002 012 Aqr
06 Mar 23 21.1 -00 11 09.7 2.953 1.972 007 Psc
20 Mar 23 51.6 +03 01 09.5 2.937 1.945 004 Psc
03 Apr 00 22.7 +06 16 09.6 2.910 1.920 006 Psc
17 Apr 00 54.4 +09 31 09.7 2.873 1.897 011 Psc
01 May 01 27.0 +12 39 09.7 2.827 1.878 016 Psc
15 May 02 00.4 +15 35 09.8 2.773 1.862 021 Ari
29 May 02 34.7 +18 15 09.8 2.713 1.850 025 Ari
12 Jun 03 09.8 +20 32 09.8 2.646 1.841 030 Ari
26 Jun 03 45.7 +22 24 09.8 2.574 1.837 035 Tau
10 Jul 04 21.9 +23 45 09.8 2.496 1.836 040 Tau
24 Jul 04 58.1 +24 34 09.8 2.412 1.839 045 Tau
07 Aug 05 33.7 +24 51 09.8 2.322 1.846 050 Tau
21 Aug 06 08.3 +24 35 09.8 2.226 1.857 056 Gem
04 Sep 06 41.1 +23 50 09.8 2.123 1.872 062 Gem
18 Sep 07 11.7 +22 40 09.7 2.014 1.890 068 Gem
02 Oct 07 39.4 +21 11 09.6 1.898 1.911 075 Gem
16 Oct 08 03.7 +19 29 09.5 1.777 1.935 083 Cnc
30 Oct 08 23.8 +17 42 09.4 1.652 1.961 092 Cnc
13 Nov 08 39.1 +15 57 09.2 1.528 1.990 102 Cnc
27 Nov 08 48.5 +14 25 09.0 1.410 2.021 114 Cnc
11 Dec 08 51.1 +13 12 08.7 1.304 2.054 127 Cnc
25 Dec 08 46.5 +12 26 08.4 1.223 2.088 142 Cnc
*********************************************************
*********************************************************
0h UT (J2000) Mag Δ r El. Con
DATE R.A. Decl. V A.U. A.U. o
hh mm.m o ′
*********************************************************
08 Jan 08 35.3 +12 11 08.1 1.178 2.123 158 Cnc
22 Jan 08 20.3 +12 22 07.9 1.179 2.158 172 Cnc
05 Feb 08 05.6 +12 49 08.2 1.232 2.195 164 Cnc
19 Feb 07 55.3 +13 20 08.7 1.333 2.232 148 Gem
05 Mar 07 51.2 +13 46 09.1 1.474 2.269 133 Gem
19 Mar 07 53.5 +14 01 09.5 1.646 2.305 120 Gem
02 Apr 08 01.3 +14 02 09.8 1.836 2.342 108 Cnc
16 Apr 08 13.5 +13 47 10.1 2.039 2.378 097 Cnc
30 Apr 08 28.7 +13 15 10.3 2.246 2.414 087 Cnc
14 May 08 46.2 +12 26 10.5 2.453 2.449 078 Cnc
28 May 09 05.3 +11 22 10.7 2.654 2.484 069 Cnc
11 Jun 09 25.4 +10 03 10.8 2.847 2.517 061 Leo
25 Jun 09 46.1 +08 32 10.9 3.028 2.550 053 Leo
09 Jul 10 07.2 +06 48 11.0 3.194 2.581 045 Leo
23 Jul 10 28.5 +04 55 11.0 3.343 2.612 038 Sex
06 Aug 10 49.9 +02 54 11.0 3.471 2.641 030 Sex
20 Aug 11 11.3 +00 46 11.0 3.577 2.669 022 Leo
03 Sep 11 32.7 -01 24 10.9 3.659 2.696 015 Leo
17 Sep 11 53.9 -03 38 10.8 3.715 2.722 008 Vir
01 Oct 12 15.0 -05 53 10.8 3.744 2.746 004 Vir
15 Oct 12 36.0 -08 05 10.9 3.744 2.769 010 Vir
29 Oct 12 56.7 -10 15 11.1 3.716 2.791 018 Vir
12 Nov 13 17.1 -12 20 11.2 3.658 2.811 027 Vir
26 Nov 13 37.0 -14 18 11.3 3.572 2.830 036 Vir
10 Dec 13 56.1 -16 08 11.3 3.459 2.847 045 Vir
24 Dec 14 14.3 -17 47 11.3 3.321 2.863 054 Vir
*********************************************************
*********************************************************
0h UT (J2000) Mag Δ r El. Con
DATE R.A. Decl. V A.U. A.U. o
hh mm.m o ′
*********************************************************
07 Jan 14 31.2 -19 16 11.2 3.162 2.877 064 Lib
21 Jan 14 46.1 -20 32 11.2 2.986 2.890 075 Lib
04 Feb 14 58.6 -21 35 11.1 2.799 2.901 086 Lib
18 Feb 15 07.9 -22 24 10.9 2.607 2.911 098 Lib
03 Mar 15 13.2 -22 55 10.7 2.420 2.919 111 Lib
17 Mar 15 13.7 -23 08 10.5 2.248 2.925 124 Lib
31 Mar 15 09.2 -22 58 10.2 2.102 2.931 139 Lib
14 Apr 14 59.9 -22 22 09.9 1.995 2.934 155 Lib
28 Apr 14 47.3 -21 21 09.6 1.938 2.936 171 Lib
12 May 14 33.8 -20 02 09.6 1.937 2.937 170 Lib
26 May 14 22.0 -18 40 09.9 1.991 2.936 154 Lib
09 Jun 14 13.9 -17 28 10.2 2.094 2.933 139 Vir
23 Jun 14 10.5 -16 38 10.5 2.234 2.929 124 Vir
07 Jul 14 11.7 -16 13 10.7 2.399 2.923 111 Vir
21 Jul 14 17.1 -16 13 10.9 2.579 2.916 099 Vir
04 Aug 14 26.2 -16 32 11.1 2.764 2.907 088 Lib
18 Aug 14 38.3 -17 08 11.2 2.946 2.897 077 Lib
01 Sep 14 53.0 -17 54 11.2 3.119 2.885 067 Lib
15 Sep 15 09.8 -18 47 11.3 3.278 2.872 058 Lib
29 Sep 15 28.6 -19 42 11.3 3.418 2.857 049 Lib
13 Oct 15 48.9 -20 35 11.3 3.536 2.841 040 Sco
27 Oct 16 10.6 -21 24 11.2 3.629 2.823 031 Sco
10 Nov 16 33.4 -22 05 11.1 3.695 2.803 022 Oph
24 Nov 16 57.2 -22 36 11.0 3.733 2.783 014 Oph
08 Dec 17 21.8 -22 54 10.8 3.741 2.761 005 Oph
22 Dec 17 46.8 -22 58 10.7 3.719 2.737 003 Sgr
*********************************************************
************************ Opposition Conjunction ************************ 05 Aug 2006 26 May 2007 *************************
The user applying this data for any purpose forgoes any liability against the author. None of the information should be used for either legal or medical purposes. Although the data is accurate as possible some errors might be present. The onus of its use is place solely with the user.