................................................................. . = T H E M A R T I A N C H R O N I C L E = . . . . The electronic newsletter by the International Mars Patrol, . . an observing program of the . . Association of Lunar and Planetary Observers . . Edited by: J.D. Beish . . August 1991 No. 7 . ................................................................. PREPARE FOR THE NEXT APPARITION OF MARS The 1990 Apparition of Mars is over and we wish to thank those brave souls who attempted, and often succeeded, in observing Mars during a period when Earth's weather did not cooperate fully. Although Mars will not appear as large in our telescopes during the next apparition, the Red Planet will be high the sky in 1993 for us Northern Hemisphere observers. With opposition falling on January 7, 1993, some of our observers will no doubt brave the cold mornings and nights to record the northern hemisphere of Mars. Hopefully, observing conditions will be improved. MARS IN 1992 AND 1993 For observers located in the northern hemisphere of Earth; sum- mer, autumn, and early winter of 1992-1993 will provide an oppor- tune time to investigate the northern hemisphere of Mars. Over the last five years, the southern hemisphere of Mars has been exposed to ground-based observers; however, the next four apparitions, 1993, 1995, 1997, and 1999, will be Aphelic. So, Mars' northern hemisphere will be most favorably positioned for us. For many observers Mars' north will be a new experi- ence. Mars will be favorably placed in the sky, north of the celestial equator throughout the entire 1992-93 apparition. The term "apparition" refers to the time span during which a planet is observable, i.e. from when one first can view the planet after it emerges from conjunction into the morning dawn sky to the time just before the next conjunction, when the planet is seen low in the western sky after sunset. Practically speaking, however, quality telescopic observations of Mars commence when its apparent diameter is greater than 6 arc-seconds. Furthermore, at the extremes of the apparition, Mars is low in the sky, where turbulence of Earth's atmosphere is severe. Despite these problems A.L.P.O. astronomers are encouraged to make observations even at these times. A red (Wratten 25 or equivalent) filter lessens the apparent seeing effects, since red wavelengths are refracted less, and improves image contrast. While little or no fine detail can be discerned when the planet is low and of small apparent size, gross features, such as Syrtis Major, can be seen. If the observer has been regularly recognizing such features and suddenly notes their disappear- ance, one is led to suspect an obscuration, such as a dust storm. Mars has an average 15.8-year seasonal opposition cycle, which consists of three or four aphelic oppositions and three convec- tive perihelic oppositions. The 1992-93 apparition will be considered an aphelic apparition because opposition occurs only 48 degrees before aphelion (70dg Ls). Mars will be closest to Earth on January 3, 1993 (20 dg. Ls) and will reach opposition on January 7, 1993 (22 dg. Ls). MARS OBSERVER SPACECRAFT and GROUND-BASED SUPPORT The Mars Observer Space probe will be launched in mid-Septem- ber 1992 and arrive for a three month calibration/test period 353 days later in September 1993. Mars Observer will begin a full scale investigation of the Red Planet in a polar orbit on 29 November 1993 and is scheduled to continue its surveillance a full Martian year through October 1995. This period will provide Earth-based observers with an opportunity to record, from a distance, the planet Mars while receiving close up observations from a Mars orbiting space station. The 1992-93 and 1994-95 apparitions of Mars will be important for IMP as well as for the professional planetary scientists. CALENDAR OF EVENTS -- MARS, 1992-93 DATE PHENOMENA ---- ---------------------------------------------------- 23 Apr 92 Disk diameter is now 4.8 arcsec. Maximum earthward tilt of 25 dg. of the Martian North pole for this apparition. Dust clouds may be present. 10 May 92 Disk diameter is now 5 arcsec. Mars crosses into celestial northern hemisphere. Dust? 15 May 92 Mars at Perihelion, watch for dust clouds. Major dust storms have been reported in the past during this Martian season (1956, 1971, 1973, and 1977). Blue and white cloud activity at minium. 16 Jun 92 Northern Winter/Southern Summer Solstice. Mars' north polar region covered with bright hood. North Polar Cap (SPC) should be near maximum diameter. Disk diameter only 5.5 arcseconds ("). Mars rises 3.5 hours before Sun. 18 Jul 92 Mars 6 arcsec. Look for orographics clouds (violet filter). 29 Aug 92 Disk diameter is now 6.9 arcsec. Major dust storms have occurred during thius period (1956, 1971, 1973, and 1977). 30 Oct 92 Disk diameter is now 10 arcsec. NPC large, hood present. Quality micrometer measurements of NPC possi- ble. Views of surface details better. Some photogra- phy now possible. Discrete (white) clouds and white areas should be seen. Measure latitude of NPH. 21 Nov 92 Northern Spring/Southern Autumn Equinox. Disk diame- ter is now 11.8 arcsec. NPH breaking up, NPC should be exposed. 23 Nov 92 Disk diameter is now 12 arcsec. Begin high resolution visual observations and high quality photography be- gins. Blue and white clouds increasing in number and brightness. 03 Jan 93 Closest Approach at 1336 UT, Mars 14.95 arcsec. Mars is at largest apparent diameter this apparition. 07 Jan 93 Opposition at 2237 UT, Dec=26 dg, De=7.5 dg, Disk diameter is now 14.9 arcsec. 30 Jan 93 eclination at 27 dg, Disk diameter now 13.8 arcsec. 13 Apr 93 NPC Rima Tenuis reported during this season. (1980, 1982, and 1984). 23 Apr 93 Aphelion, Declination 23.7 dg, disk diameter is now 6.6 arcsec. Increasing cloud activity. 08 Jun 93 Northern Summer/Southern Winter Solstice. Orographics over the Tharsis volcanoes -- W-Cloud? Blue and white clouds numerous and bright in blue and violet filters. Mars 5.1 arcsec in apparent diameter, Declination 15.7 dg. ---------------------------------------------------------------- APPARITIONS OF MARS FOR THE NEXT TEN YEARS Opposition Dec. Closest Dia. Photographic Period Date dg Approach arcsec 12 arcsec or more 1993 Jan 07 26.0 1993 Jan 03 14.95 1992 Nov 23 - 1993 Feb 11 1995 Feb 12 18.0 1995 Feb 11 13.85 1995 Jan 11 - 1995 Mar 16 1997 Mar 17 04.7 1997 Mar 20 14.20 1997 Feb 15 - 1997 Apr 26 1999 Apr 24 -11.6 1999 May 01 16.18 1999 Mar 16 - 1999 Jun 25 2001 Jun 13 -26.5 2001 Jun 21 20.79 2001 Apr 15 - 2001 Sep 15 2003 Aug 28 -15.8 2003 Aug 27 25.11 2003 May 29 - 2003 Nov 22 SEASONS OF MARS Mars has seasonal periods similar to Earth's. Mars and Earth have four comparable seasons because their axes of rotation are each tilted at about the same angle to their respective orbital planes. Mars' axial tilt is 25.2 degrees as compared to 23.5 degrees for that of the Earth. The Martian year is 687 Earth days, nearly twice as long as ours, so that the Martian seasons are similarly longer. While Earth's are nearly equal in dura- tion, the length of a Martian season can vary by as much as 51 days because of the greater eccentricity of the orbit of Mars. Areocentric Martian Season Duration of seasons longitude Northern Southern Mars Earth of the Sun Hemisphere Hemisphere Ls (dg) Sols Days Days ----------------------------------------------------------- 000 - 089 Spring Autumn 194 199 92.9 090 - 179 Summer Winter 178 183 93.6 180 - 269 Autumn Spring 143 147 89.7 270 - 360 Winter Summer 154 158 89.1 --- ---- ----- 669 687 365.3 note: Days = (23h 56m 4.09s) Sols = Martian days (24h 37m 22.665s) Ls = Areocentric longitude of the Sun. HISTORY OF ALPO MARS OBSERVATIONS -------Ls------ Opposition Ls Observation Dates Span Range 1968 May 31 165 1968 Nov 22 - 1970 Mar 12 075 - 336 262 1971 Aug 10 232 1970 Nov 29 - 1972 Feb 18 097 - 347 251 1973 Oct 25 306 1973 Feb 24 - 1974 May 19 160 - 050 251 1975 Dec 15 357 1975 Mar 18 - 1976 Jul 19 197 - 096 260 1978 Jan 22 036 1977 Jun 26 - 1978 Aug 05 286 - 124 199 1980 Feb 25 070 1979 Jun 06 - 1980 Oct 22 300 - 187 248 1982 Mar 31 105 1981 Jul 28 - 1983 Jan 01 354 - 238 245 1984 May 11 145 1983 Aug 11 - 1985 Mar 29 021 - 331 311 1986 Jul 10 202 1985 Sep 19 - 1987 Jun 22 059 - 038 340 1988 Sep 28 280 1987 Nov 09 - 1989 Jun 12 100 - 053 314 1990 Nov 27 340 1990 Jan 25 - 1991 May 24 157 - 064 268 NUMBER OF OBSERVATIONS Opposition Observers Visual Photo Microm CCD Total 1969 May 31 31 415 6 0 0 421 1971 Aug 10 115 1633 345 0 0 1978 1973 Oct 25 78 1050 305 0 0 1355 1975 Dec 15 54 888 124 0 0 1012 1978 Jan 22 30 494 38 0 0 532 1980 Feb 25 41 1118 45 145 0 1308 1982 Mar 31 56 1551 143 309 0 2003 1984 May 11 57 1267 194 149 0 1610 1986 Jul 10 90 1623 555 172 0 2350 1988 Sep 28 306 4818 2038 191 16 7063 1990 Nov 27 75 1067 536 22 44 1669 --------------------------------------------------------- Average 53 1451 394 90 5 1940 Total 935 15958 4329 988 60 21335 Note 1. Photographic Period refers to the ideal apparent diameter for most telescopes, "Dec" refers to the declination, and "Dia" is the apparent diameter of Mars. Note 2. Ls is the Planetocentric longitude of the Sun, reckoned from 0 degrees as the first day of northern spring on Mars. Note 3. ALPO Mars observations began in 1947. This history reflects only those observations cataloged by the ALPO Mars Section at this time. Note 4. "Actual" refers to the actual number of degrees Ls that were observed, Micro refers to polar cap micrometer measurements, and CCD refers to the number of tapes of CCD imaging of Mars. MISCELLANEOUS INFORMATION ABOUT MARS Equatorial diameter of Mars ........ 6778.84 km (4212.16 mi) Rotation period .................... 350.891986 dg/day Sidereal day ....................... 24h 37m 22.655s Solar day .......................... 24h 39m 35.238s Sidereal year ...................... 686.97964 days Synodic period ..................... 779.94657 days Simi-major axis .................... 227,970,000 km (1.52 A.U.) Perihelion distance ................ 206,650,000 km (1.38 A.U.) Aphelion distance .................. 249,180,000 km (1.67 A.U.)