Note: Archive copy. Original site was: http://www.tnni.net/~dustymars/2007_Mars.htm

THE 2007 APHELIC APPARITION OF MARS
By: Jeffrey D. Beish

ABSTRACT

Always an intriguing world, Mars offers both casual and serious observers many challenges and delights. It also provides astronomers a laboratory to study the atmosphere and surface of another planet, including the behavior of condensates and their effects on its atmosphere and surface. Mars is similar to Earth in that it has four seasons, exhibits global climates, changing weather patterns, annual thawing and growing of polar caps, storm clouds of water ice, howling dusty winds, and a variety of surface features that predictably change in color and size and appear to shift position over extended periods of time.


INTRODUCTION

Mars appears more Earth-like to us than most of the other planets because we can observe its surface, atmospheric clouds and hazes, and its brilliant white polar caps. The latter are composed of frozen CO2 and underlying water ice, and wax and wane during the Martian year. These aspects, along with the changing seasons and the possibility of life, have made Mars one of the most studied planets in our solar system.

The Red Planet Mars offers both casual and serious observers many challenges and delights, as well as providing astronomers a laboratory to study another planet's atmosphere and surface. Some Martian features even appear to shift position around the surface over extended periods of time.

There are several cooperating international Mars observing programs under way to assist both professional and amateur astronomers. These include the International Mars Patrol (I.M.P.) coordinated by the Mars Section of the Association of Lunar and Planetary Observers (A.L.P.O), the International MarsWatch, the Terrestrial Planets Section of the British Astronomical Association (B.A.A.), and the Mars Section of the Oriental Astronomical Association (O.A.A.).

Information for observing Mars during a typical apparition is presented in a separate report titled, "General Information for Apparitions of Mars." This report can be found on the Internet at URL: http://www.tnni.net/~dustymars/General_Info_Mars.htm

With the advent of modern CCD camera technology the amateur can produce useful images of Mars when it is as small as 3.5 arcsec. Early in an apparition, Mars rises in the east or morning sky and sets with the rotation of the Earth in the western or evening sky. During the past few apparitions (2001-2005), observers began to take CCD images when Mars was only 32 degrees away from the Sun. Since Mars was only a visual magnitude of ~1.8 then the planet would have been difficult to locate bright twilight hours.

In the pre-apparition reports the observer will find the motion of Mars in our sky, the characteristics for that particular apparition, information pertaining to the polar cap(s) and any special events that may be seen during that particular apparition. As usual a calendar of events will be included with each report that contains cardinal dates for seasonal activity and orbital information of Mars.

MOTION OF MARS IN OUR SKY

As a general rule, an "apparition" begins when a planet emerges from the glare of the Sun shortly after conjunction. Mars will be in conjunction when the Sun on October 23, 2006 (124.5deg Ls); however, Mars will disappear behind the Sun around October 11, 2006 and will not emerge from the Sun until 24 days later on November 04.

The apparent declination of Mars begins at -23.2deg in mid-January 2007, and then begins to climb northward until crossing through the celestial equator on May 21, 2007 in the constellation Pisces. Mars continues to increase in declination and will reach 26.7deg on opposition day. This is good news for those observing in the Northern Hemispheres because Mars will be seen high in their sky. Mars will continue to be above the celestial equator to the remainder of the apparition crossing from the constellation Pisces into Aries during the end of June. By September 18, 2007, a '0' visual magnitude Mars is seen rising early in the morning sky in the constellation Taurus, it will be at western quadrature (90deg west of the Sun) and the phase or terminator will be at its widest (44deg).

In 2007 Mars begins retrogression, or retrograde motion against the background stars nearly thirteen months after conjunction November 16, 2007 (348deg Ls) through January 31, 2008 (25.2deg Ls). Each night for this brief period before, during and after opposition the Red Planet will appear to move backwards toward the western sky from the constellation Gemini into Taurus.

Since the Martian year is about 687 Earth days long -- nearly twice as long as ours, the Martian seasons are similarly extended. While the Earth's seasons are nearly equal in duration, the Martian seasons can vary by as much as 52 days from each other due to that planet's greater orbital eccentricity (see Figure 1)

Figure 1. A heliographic chart of the orbits of Mars and the Earth showing the relative seasons of both planets in the planetocentric longitude system Ls. Graphic Ephemeris for the 2007 Aphelic Apparition of Mars. Original graph prepared by C.F. Capen and modified by J.D. Beish.


2007 APPARITION CHARACTERISTICS

Another general rule for predicting oppositions of Mars is from the following: the planet has an approximate 15.8-year periodic opposition cycle, which consists of three or four Aphelic oppositions and three consecutive Perihelic oppositions. Perihelic oppositions are also called "favorable" because the Earth and Mars come closest to each other on those occasions. We sometimes refer to this as the seven Martian synodic periods. This cycle is repeated every 79 years (+/- 4 to 5 days) and, if one were to live long enough, one would see this cycle nearly replicated in approximately 284 years. The 2007 Mars apparition is considered transitional because the orbital longitude at opposition will be only 63deg from the aphelion longitude 70deg Ls (Ls will be defined later).

Closest approach occurs at 0018 UT on December 19, 2007 (4.7deg Ls) with an apparent planetary disk diameter of 15.9'' at a distance of 0.589466803488 astronomical units (AU) or 54,794,253 miles (88,182,979 km). [NOTE: one (1) A.U. equals 92,955,621 miles or 149,597,870 km]. It should also be noted that closest approach between Earth and Mars is not necessarily coincident with the time of opposition but varies by as much as two weeks.

Opposition occurs fourteen months after conjunction, when Mars is on the opposite side of the Earth from the Sun. At that time, the two planets will lie nearly in a straight line with respect to the Sun, or five weeks after that retrogression begins. Opposition will occur at 1941 UT on December 24, 2007 (7.1deg Ls), with an apparent planetary disk diameter of 15.8 arcsec. Mars will remain visible for eleven months after opposition and then become lost in the glare of the Sun again (November 23, 2008) as it approaches the next conjunction (December 05, 2008). The cycle is complete in 780 Earth days.

Figure 2. A simulated view of the appearance of Mars during opposition at 1941 UT on December 24, 2007 (7.5deg Ls).


The observable disk diameter of Mars will be greater than 6 arcsec from June 14, 2007 [7.2deg d] (257.1deg Ls) and will not fall below this value until April 24, 2008 (62.8deg Ls), lasting 10 and a half months or 166 degrees Ls. During a similar profile in 2005 Mars began at 6 arcsec on April 07, 2005 [-19.6deg d] (188.7deg Ls) and continued March 24, 2006 (29.3deg Ls), equaling 11 and a half months or 200 degrees Ls. Imaging by CCD devices may begin with a disk diameter of 4 arcsec or less, commencing on January 10, 2007.

During closest approach in 2007 the apparent diameter of Mars will be more than 4 arcsec smaller than it was at the same period in 2005; however, it will be 10 degrees higher in the sky much better for observing the Red Planet helping to make up for the smaller size.

The Sub-Earth (De) and Sub-Solar (Ds) points are graphically represented in Figures 3 and 4. The 2007 and 2008 Ephemeris of Mars is tabulated the following URL: http://www.tnni.net/~dustymars/eph07_08.html A glossary of Terms appears at the end of this table.

Figure 5 graphically illustrates the ephemeris of Mars for 2007, showing the apparent diameter of the planet. Figure 6 illustrates the Martian apparitions for 2001, 2003, 2005 and 2007.

Figure 3. As it approaches Earth, it will swell from a small apparent disk of 6" in June 14, 2007 to a maximum diameter on December 18, 2007, and then shrink as it moves away. Closest approach occurs on December 19, 2007 (Opposition December 24, 2007). From June 2007 through April 2008 are the prime observing months.


Figure 4. Graphic Ephemeris of Mars during the 2007-2008 apparition from January 1, 2007 through December 31, 2008. Opposition and 6 arcsec apparent diameter range arc indicated. Plot illustrates the Declination (black line), the latitude of the Sub-Earth point (De) or the apparent tilt (brown line) in areocentric degrees, and the latitude of the Sub-Solar point (green line) in areocentric degrees. The areocentric longitude (Ls) of the Sun, shown along the bottom edge of the graph defines the Martian seasonal date. The value of Ls is 0deg at the vernal equinox of the northern hemisphere, 70deg when Mars is at aphelion, and 90deg at the summer solstice of the northern hemisphere 250deg when Mars is at perihelion, and 180deg is northern autumn.


Figure 5. Graphic Ephemeris of Mars from January 1, 2007 through December 31, 2008 Plot illustrates the apparent diameter of Mars in seconds of arc. The areocentric longitude (Ls) of the Sun, shown along the bottom edge of the graph defines the Martian seasonal date.
Figure 6. Graphic plot comparing the declination of Mars during the 2001, 2003, 2005 and 2007 apparitions. The Areocentric longitude (Ls) of the Sun, shown along the bottom edge of the graph, defines the Martian seasonal date. Oppositions years are shown at top of vertical lines. Opposition date 2001[177deg Ls] - (blue line), for 2003[249deg Ls] - (green line), 2005 [320deg Ls] - (orange line), and 2007 [7deg Ls] (violet line).
THE NORTH AND SOUTH POLAR REGIONS

Astronomers will have a view of both polar regions during the next apparition. On January 9, 2007 the Martian South Polar Region (SPR) began to tilt toward the Earth and will remain so until September 13th when it reaches 0deg De. Also, the terminator may begin to cover the cusp of the polar cap because the Ds will then begin to move southward, or more negative, along with the southward direction of the De. After that, the South Pole will be in the shadow of the southern portion of the limb terminator. By the first week week in March (195deg Ls), the SPC should be free of its hood, enough so to begin micrometer measurements. The north polar region will begin to tilt towards Earth in september and remain positive until the end of 2007. For more detailed information on the south polar cap go to and click: http://www.tnni.net/~dustymars/SPR.htm
or the north polar cap click:
http://www.tnni.net/~dustymars/NPR.htm

DUST STORMS

Observations of Mars indicate that major dust storms tend to be more frequent when Mars is closest to the Sun during southern hemisphere spring and summer. While predicting these events is nearly impossible to make our studies show that the Martian dusty season should begin about the third week in May (241deg Ls) throughout the first week in July 2007 (270deg Ls). The highest probability of dust storms occurring will be on or about June 11, 2007 (255deg Ls) and a sensitive area for the development of dust storms is in northwest Hellas.

Massive, planet-encircling storms usually occur in southern hemisphere summer and that will come by the middle of September (315deg Ls). Observers should be alert for dust clouds in the northeast Hellas Basin, the Serpentis-Noachis region, and the Solis Lacus region. If the Red Planet behaves as it did in 2001 and 2003, then 2007 may be a time when Mars may be very dusty indeed! For more detailed information on Martian dust storms click to the URL: http://www.tnni.net/~dustymars/2003_DUST.htm

SPECIAL EVENTS

For those interested in catching a glimpse of possible "flashes" from the surface of Mars there will be two periods when possible "flashes" may be seen on Mars. When the De and Ds are coincident will be on or about December 20, 2007. See table below for dates when De = Ds +/- 1.0deg:

First Period: EST = UT - 4 || Di = 5.7" 5.9"

Date
Rise
Transit (EDT)
De
Ds
De - Ds
i
May 28
0734
1344 (0944)
-23.6
-22.6
1.0
37.9
May 29
0732
1343 (0943)
-23.5
-22.7
0.8
38.0
May 30
0731
1341 (0941)
-23.4
-22.8
0.6
38.1
May 31
0729
1340 (0940)
-23.3
-22.9
0.4
38.3
June 01
0727
1339 (0939)
-23.2
-23.0
0.2
38.4
June 02
0725
1338 (0938)
-23.1
-23.1
0.0
38.5
June 03
0723
1337 (0937)
-22.9
-23.2
-0.3
38.6
June 04
0722
1336 (0936)
-22.8
-23.3
-0.5
38.7
June 05
0720
1334 (0934)
-22.7
-23.4
-0.7
38.8
June 06
0718
1333 (0933)
-22.5
-23.5
-1.0
38.9

Second Period: EST = UT - 5 || Di = 15.9"

Date
Rise
Transit (EST)
De
Ds
De - Ds
i
December 18
2257
0606 (0119)
2.6
1.7
0.9
6.3
December 19
2251
0601 (0114)
2.4
1.9
0.5
5.5
December 20
2246
0555 (0108)
2.2
2.2
0.0
4.7
December 21
2240
0549 (0103)
2.0
2.4
-0.4
3.9
December 22
2234
0543 (0058)
1.8
2.6
-0.8
3.2
                 NOTE: Di = apparent diameter of Mars
                                    De = Declination of Earth from Mars
                                    Ds = Declination of Sun from Mars
                            De - Ds = coincident
                                        i = phase defect in degrees


Table 2. CALENDAR OF EVENTS -- MARS, 2007

DATE PHYSICAL REMARKS
2006 Oct 10 Ls 118deg Conjunction Ingress. Mars will disappear behind the limb of the Sun.
2006 Oct 23 Ls 125deg Conjunction. Mars is behind the Sun ~2.5939 AU.
2006 Nov 07 Ls 132deg Conjunction Egress. Mars will emerge from behind the limb of the Sun.
2007 Feb 08 Ls 180deg
De -9.5deg
Ds -0.1deg
RA 19:11
Dec -23.1deg
A.Dia 4.3
Equinox - Northern Autumn/Southern Spring.South Polar Cap (SPC) maximum diameter, subtending ~ 60.5deg W. Is the North Polar Hood present. Does SPH or frost cover Hellas? Hellas should begin to clear and darken. Are W-clouds present? South cap emerges from darkness of Winter. SPH thinning and forms "Life Saver Effect."
2007 Jun 03 Ls 250.2deg
De -22.9deg
Ds -23.2deg
RA 00:53
Dec 4.1deg
A.Dia 5.8
Mars at Perihelion.Late southern spring. SPC in rapid retreat. Novus Mons smaller. Dust clouds expected over Serpentis-Hellaspontus (Ls 250deg - 270). Syrtis Major narrow. Frost in bright deserts? Orographic clouds (W-clouds) possible. Elysium and Arisa Mons bright? Frost in bright deserts? Novus Mons smaller. Note: Several "planet-encircling dust storms have been reported during this season. High probability 255deg Ls. . (SPC W ~ 25.0deg +/-2.6deg).
2007 Jun 14 Ls 257.1deg
De -21.3 deg
Ds -24.1deg
RA 01:23
Dec 7.2deg
A.Dia 6
Apparition begins for observers using 4-inch to 8-inch apertures telescopes and up. Begin low-resolution CCD imaging. Views of surface details not well defined. Novus Mons reduced to a few bright patches and soon disappears. Windy season on Mars begins, dust clouds present? Watch for initial dust clouds in south. White patches in bright areas? Hellas bright spots? Numerous bright patches (SPC W ~ 20.8deg +/-1.0deg).
2007 Jul 05 Ls 270deg
De -17.1deg
Ds -24.8deg
RA 02:21
Dec 12.6deg
A.Dia 6.4
Solstice - Northern Winter/Southern Summer. W-clouds present? NPH extends 50deg N? Decreased number of White clouds. Atmosphere clearing of blue clouds? White areas in deserts? Dust clouds in south until 270deg Ls? Watch for planetary system clouds bands? (SPC W ~17.7deg +/-1.2deg).
2007 Aug 29 Ls 304.1deg
De -03.4deg
Ds -20.3deg
RA 04:49
Dec 21.6deg
A. Dia 8
White areas? Orographic clouds over the Tharsis volcanoes. W-Cloud? SPC very small, difficult to see.(SPC W ~ 10.2 +/-0.5deg).
2007 Oct 06 Ls 325.9deg
De 4.4deg
Ds -13.6deg
RA 06:13
Dec 23.5deg
A.Dia 10
Wave or frontal cloud activity from NPR? Bright spots in Hellas?
Hellas Ice-fog activity?(SPC W ~9.4deg +/-0.5deg).
2007 Oct 30 Ls 339.0deg
De 7.0deg
Ds -8.6deg
RA 06:46
Dec 23.9deg
A.Dia 12
NPC large hood present. W-Cloud? Orographic cloud over Arsia Mons? Topographic cloud over Libya? Topographic cloud over Edom?
2007-Nov-16 Ls 348deg
De 7.0deg
Ds -5.0deg
RA 06:54
Dec 24.5deg
A.Dia 13.7
Retrogression Begins. Mars begins retrogression, or retrograde motion against the background stars nearly 390 days after conjunction, when it appears to move backwards toward the west for a brief period before, during and after opposition.
2007 Dec 10 Ls 0.0deg
De 4.2deg
Ds 0.0deg
RA 06:36
Dec 26.0deg
A.Dia 15.7
Equinox - Northern Spring/Southern Autumn. North Polar Hood (NPH) breaking up, North Polar Cap (NPC) should be exposed and near to 55deg areographic latitude. ("Areo-" is a prefix often employed when referring to Mars or "Ares.")
2007 Dec 18 Ls 0.4deg
De 2.6deg
Ds 1.7deg
RA 06:23
Dec 26.5deg
A.Dia 15.9
Mars at Closest Approach. High-resolution CCD imaging and photography.
2007 Dec 24 Ls 7.1deg
De 1.4deg
Ds 3.0deg
RA 06:13
Dec 26.7deg
A.Dia 15.8
Mars at Opposition.North Polar Hood (NPH) breaking up, North Polar Cap (NPC) should be exposed Hellas and Argyre bright? (NPC Width ~65deg).
2008-Jan-31 Ls 25.2deg
De -2.5deg
Ds 10.3deg
RA 05:33
Dec 26.7deg
A.Dia 12.2
Retrogression Ends.Mars begins westward motion against the background stars.

2008 Feb 01 Ls 25.6deg
De -2.5deg
Ds 10.4deg
RA 05:33
Dec 26.7deg
A.Dia 12
NPC nearly static or entering erratic retreat, hood dissipating? Limb clouds and hazes should start to increase. (NPC Width ~65deg).
2008 Feb 20 Ls 34.3deg
De -1.2deg
Ds 13.7deg
RA 05:43
Dec 26.4deg
A.Dia 10
Limb clouds and hazes should start to increase. Few clouds. Limb arcs increasing in frequency or intensity? Arctic hazes and clouds?
(NPC W ~43.4deg).
2008 Mar 15 Ls 45.1deg
De 2.4deg
Ds 17.3deg
RA 06:16
Dec 26.0deg
A.Dia 8
Few clouds. Limb arcs increasing in frequency or intensity? Arctic hazes and clouds? (NPC W ~46.0deg +/-1.4deg)
2008 Apr 24 Ls 62.8deg
De 10.5deg
Ds 21.9deg
RA 07:35
Dec 23.6deg
A.Dia 6
Watch for "Aphelic Chill" in North Polar region (NPR) (usually between 60deg and 70deg Ls) and possible halt in thawing of NPC. Views of surface details well defined. Rima Tenuis may appear (140deg and 320deg areographic meridians). Cloud activity in north increasing? (NPC W ~44.5deg +/-1.0deg).
2008 May 11 Ls 70deg
De 14.1deg
Ds 23.2deg
RA 08:12
Dec 21.7deg
A.Dia 5.6
Mars at Aphelion. Is North Cap fairly static or entering rapid retreat phase. Watch for "Aphelic Chill" in NPR (usually between 60deg and 70deg Ls). Antarctic hazes, hood. South polar regions becoming difficult to observe. Any signs of SPH? Cloud activity increases. Are limb arcs increasing in frequency, intensity? (NPC W ~37.4deg +/-0.8deg)..
2008 Nov 21 Ls 161deg Conjunction Ingress.Mars will disappear behind the limb of the Sun.
2008 Dec 05 Ls 169deg Conjunction. Mars is behind the Sun ~2.477AU.