MARS OPPOSITION OF 2010 --------------------- John Pazmino NYSkies Astronomy Inc firstname.lastname@example.org www.nyskies.org 2010 January 4
Introduction ---------- Mars in his orbit around the Sun passes by Earth once in about two years and seven months. When he lines up with Earth and Sun, he is near his closest distance from Earth. Mars and Earth are then on the same side of the Sun in their orbits. From Earth's eye, Mars is on the line from Sun thru Earth to Mars. To see Mars we face away from the Sun, so this aspect of Mars relative to Sun and Earth is called opposition. At other times we look toward various angles away from the Sun, but not directly opposite, at 180 degrees. Mars has an orbit more elliptical than Earth's. His distance from Earth at opposition varies widely by almost 2:1 between the closest approach when Mars is nearest to the Sun as he passes Earth and when he is farthest from Sun. The effect of this varying distance near opposition is that Mars, which already is a small planet, presents a tiny disc to us in small telescopes. It is tough enough to inspect the planet when he is at a close opposition, but in 2010 he rounds an opposition near the farthest possible distance away. The disc is then about the smallest.
Watching Mars ----------- All of this article assumes only bare eye and binocular viewing. No telescope of high magnification is discussed here. Just about any binoculars are suitable, so long as it produces clear sharp images. Dirty, banged-up, loose instruments should be repaired or discarded. Now binoculars costing mid tens to low hundreds of dollars are thoroly adequate. Expensive units are simply not needed. The binoculars should be comfortable and light and small to easily support by hand. Large heavy models require support like a camera tripod. They are clumsier to handle and less spontaneous to use. Have a star atlas by which to plot Mars among the stars. An all- 0sky starchart or a simple constellation chart has too few stars and too small a scale. A US letter size chart with Castor-Pollux on the right and Regulus on the left has a good scale. To avoid spoiling a good book of maps, work with photocopies. In 2010 Mars spends his prime time between stars Castor and Pollux and Regulus. A planetarium program or mechanical planisphere shows where in the sky these stars are. They are in the evening sky fro January thru late spring, but in different directions and altitudes above the horizon. No other planet invades this region to confuse with Mars.
Apohelion ------- In an elliptical orbit, the point closest to the Sun is the perihelion; farthest, apohelion. This is also spelled 'aphelion' but the tendency is to pronounce the 'ph' as a 'f', at least in English. The word is 'app-HEH-lee-yonn', not 'a-FEH-lee-yonn'. Leaving the 'o' in place forces the better pronunciation by separating the 'p' and 'h', 'a-poh-HEH-lee-yonn'. Because in 2010 Mars is near apohelion at opposition, this round is known as an apohelic opposition. The disc of the planet attains only 14.1 arcsecond diameter, the size of a US 25-cent coin seen from 350 meters away! This is tiny in the typical home telescopes. Most home astronomers will see little texture on the planet. In the months before and after the opposition date, the planet shrinks in size to a pink dot in most home telescopes. That's why most home astronomers storm their views of Mars within the week or so of opposition. That's when the disc is largest with better chance of discerning his surface features. This round of Mars may be a downer in the telescope if you recall the close-in, perihelic, oppositions, of 2001, 2003, and 2005.
Spaceprobes --------- Much of the news about Mars is produced by the several spaceprobes at or on Mars. More news comes from ground or Earth-orbit observatories. Follow Mars developments thru the websites of the facilities and missions. The two rovers, Spirit and Opportunity, are still working after SIX YEARS on the planet. Spirit is still jammed in loose soil while Opportunity is running freely. Efforts to free Spirit so far have failed, but JPL is exploring further attempts. The orbiting probes, like Mars Express and Mars Recon Observer, are in good working order with a dense stream of information beamed back to Earth. NASA's Mars Science Lab and Russia's Phobos-Grunt probes were not ready in time for the 2010 opposition. They had to be launched a couple months ahead of the opposition, in fall 2009. They are nearly complete, and will be ready in early 2010 but they missed the current launch window. The next launch window to visit Mars is near yearend 2011, before the 2012 opposition. During the 2010 opposition Mars is in his northern spring and summer. The south hemisphere of Mars is in autumn and winter. The north pole of Mars is tilted toward Earth, letting us to see it in the clear and the Sun to heat it.
Mars geography ------------ You really should use the pure word, 'areography' by analogy with mapping of Earth. It is increasingly common to use Earth terms with a qualifier for the instant celestial body. You will hear and see 'Mars geology' in place of 'areology' and 'Mars geophysics; for 'areophysics'. The prefix comes from the Greek name for Mars, Ares. The light and dark spots and blotches on Mars, as seen from Earth, were originally thought to be seas and land. They were given names still in use today. The regions are coarse areas of the planet, the size, in proportion, to entire countries on Earth. Spacecraft visited Mars and observed topographic features: plains, mountains, canyons, craters, cliffs, river beds, and so on. These were named separately from the dark/light names. In some cases a vague patch seen from Earth is part of a real landform on Mars. In such cases, the new name was made from the old. Nix Olympica, a white spot on Earthly maps, is really the ice and snow on top of a huge volcano, now named Mons Olympus. Thus, Mars has two independent systems of place names! The ones on Mars maps for Earth use (ground or close orbit) have the light/dark names. The light/dark scheme is also the 'albedo' scheme, based on the reflective property of the various parts of the planet. Those for use at or on Mars have the topographic names. In both systems, the names are Latin or Latinized words, requiring at the worst a continental pronunciation. Saying them like English words can result in nonsense sounds. One amazing fact is that the land area of Mars, which is the entire area of his globe, is quite equal to the land area of Earth! Recall that while Earth has four times the total global area as Mars, only a quarter of it is land. The rest is open water.
Mars seasons ---------- Mars has a regime of seasons analogous to Earth. With no open water and only a thin atmosphere, Mars does not have the same weather mechanism as Earth. When Mars's north pole is titled toward the Sun, and in view of Earth, the north hemisphere enjoy spring and summer. With the pole tilted away from Sun, and from Earth, the north hemisphere is in autumn and winter. The difference among seasons is mainly of raw influx of solar radiation and ground temperature. The seasons are roughly twice the length of Earth's, due to the Mars year being about 2 Earth years. On Earth, the seasons are about of equal length, because the orbit of Earth is nearly circular and Earth travels in it at about the same speed all year long. The Mars seasons vary widely in length due to the more excentric orbit of the planet. The planet spends a greater or lesser time in each season according as the varying speed of the planet in his orbit.
Time and calendar --------------- As yet there is no global system of calendar or time for Mars. many schemes are proposed but none earned general favor over an other; As an example, the two Mars rovers count elapsed Mars days starting from their own landing on the planet. Opportunity started work a couple days after Spirit, making their day counts out of synch. A common name for a day on Mars, or on any other planet, is 'sol'. Most schemes skip dividing the Mars year into anything like weeks or months. These units on Earth are based on the Moon's phases or cultural legacy, both lacking on Mars. It seems best to merely assign a say count within each year, as is done for data networks and payroll management. As yet there is no agreement for a zero year. One common method of giving the place of Mars in his orbit, amounting to a Mars calendar date, is to cite the longitude of the Sun along the Mars ecliptic. This parallels the method on Earth where the location of the Sun on Earth's ecliptic is the date within the Earth year. In fact, some starcharts label the ecliptic with both degrees of longitude and calendar dates for the location of the Sun. In this system, the Mars vernal equinox is at solar longitude 0 deg, like for Earth. The summer solstice is 90 deg; autumnal equinox, 180 deg; winter solstice, 270 deg. The Mars clock hour is based on the actual longitude on Mars, there being no timezones. The Mars day is divided into 24 'hours', each then cut into 'minutes' and 'seconds'. These units are a trifle longer than those of Earth because the Mars day is 24h 37m of Earth time, 2.6% longer. This slippage of hours between Earth and Mars causes real headaches for scientists working with Mars spacecraft. They must keep track of Mars time, yet conduct their work on Earth time!
Apparition -------- The apparition of a planet is the entire span of time from when it emerges from twilight after passing by the Sun to when it is lost in twilight before passing the Sun again. There is a dead period when the planet is absent from the sky while passing the Sun. In the old days, it was impossible to follow the planet in this dead zone, also called the 'Sun gap'. With the SOHO spaceprobe photographing the sky around the Sun, you can follow a planet on the SOHO pictures! The images are too coarse to see any detail on the planet, but you satisfy yourself that the planet is moving along as it should. Mars, without the aid of SOHO, resolves out of the morning dawn as the Sun leaves it behind in darker sky. It is, due to his distance from us, a dim star of 2nd magnitude, a bit tough to discern in a bright twilight sky. By convention, the dead zone for Mars is one month before and after his conjunction with the Sun. On successive mornings, Mars edges farther from the Sun into eventually a night sky, where he is then an obvious new 'star' in the zodiac. Mars is gliding eastward thru the zodiac, just like the Sun, but at a slower pace. Mars is lagging the Sun, allowing him to be seen earlier and earlier in the night as the month roll by. When Mars falls behind the Sun to stand 90 degrees west from him, this is west quadrature, or square, or quartile. This moment is informally the start of the telescope viewing season for most home astronomers. By this time Mars is close enough to Earth to present a reasonably large (still small!) disc in the telescope and maybe something can be seen of his surface markings. Mars continues to fall behind the Sun until he seems to slow his forward march and enter the retrograde loop. This is explained more fully below. All the while, the planet is drawing nearer to Earth, growing larger in angular size and in brilliance. He is already a magnitude 0 or brighter star, outshining other stars around him. The opposition moment is in the middle of the retrograde loop, when he is running westward at the fastest pace. He is then 180 degrees west (or 180 east) of the Sun, as directly as possible opposition in the sky from the Sun. Mars at opposition is near his largest angular size and brilliance. This maximum of size and brightness is a peak that within a week is noticeably weakened. Most home astronomers storm their observing within a week or so of opposition. After opposition Mars runs a bit farther west, then slows and stops. He then leaves the retrograde loop, resuming direct, east, motion again. he is moving a bit slower than the Sun, so the Sun is now catching up to Mars, decreasing the spacing between the two bodies. Mars eventually stands 90 degrees east of the Sun, in east quadrature, and informally ends the telescope viewing season for this apparition. He is still a bright star by eye but his disc is rather too small for easy detection of surface details. Mars slowly creeps along the zodiac with the Sun gaining on him. He shrinks in size and wanes in luster. He remains a considerable star in the zodiac, easy to spot until twilight engulfs him. Eventually the twilight glow around the Sun catches up to Mars, pulling him into the dusk sky. And then Mars is swallowed in strong twilight to end the apparition. By convention this happens a month before the next solar conjunction as Mars enters the Sun gap. Mars is visible, if at an inconvenient hour, for quite two years of its two years and seven week circuit around the sky. He is lost to sight for a month before to a month after sliding around the Sun. One hideous mistake many people make is to WAIT UNTIL the night of opposition for their first look at Mars. They also cease looking immediately after opposition. Both actions crudelly ruin you of your due and owing appreciation of the celestial dance of planets. You should watch Mars routinely for several months leading to and from opposition. At the very least, cover the interval between the two squares, west and east.
Opposition and proximity ---------------------- Often these are treated as equivalent events. If the orbits of Mars and Earth were both circular and the planets coursed in them at constant speeds, the opposition and proximity would coincide. Due to the elliptical shape of the orbits and varying speeds of the planets in them, proximity and opposition almost never can coincide. proximity is the linear closest approach of Mars to Earth, the point of minimum signal travel time and all that. It occurs on January 27 with a separation of 99.33 million kilometers, about 2/3 the distance from Earth to Sun. The lineup of Mars, Earth-Sun comes on the 29th, at 99.41 million kilometers. The difference is slight, but the two events have entirely distinct definitions. Even at opposition Mars is not exactly 180 degrees from the Sun. Mars is a little north of the ecliptic on the 29th, so is a wee bit off the earth-Sun line. The separation from the Sun is a maximum, more like 178 degrees, but not quite 180. For convenience sake, we work only with the longitude of Mars, his downrange distance along the ecliptic, and ignore his displacement in latitude north or south of the ecliptic. So Mars is at opposition when his longitude is 180 degrees from the Sun's, not when he is actually 180 degrees away.
Retrograde loop ------------- All of the planets do a really sturrange act once during each of its cycles around the sky. They all after proceding eastward thru the zodiac, slow down, stop, backtrack westward. They run westward for a while at a fast pace. Then they slow again, stop, reverse, and resume direct motion. This is the retrograde loop. The effect is entirely one of perspective from Earth. We view mars, a moving planet, from Earth, an other moving planet. The line of sight from Earth to Mars swings to and fro according as the relative speeds between the two planets. The two inner planets Mercury and Venus go thru their loops in twilight or daylight. We just don't notice them. Mars and the other outer planets go thru their loops in night, where we can marvel at them. The loop is run during the weeks leading to and from opposition. Mars entered the loop on 2009 December 22. He is in retrograde at opposition in the middle of the loop on 2010 January 29. On 2010 March 11 he comes out of retrograde and takes up prograde motion again. The term 'loop' implies a circle or lasso shape. In fact the path traced out in the stars varies substantially from opposition to opposition. It ranges from a loose 'S' shape, to an aerobatic up-&- over or down-&-under curve, to a lazy back-&-forth sway. In 2010 it's an up-&-over, a bit flattened, curve. In all cases there is a definite point at each end, a cusp or vertex or apex, where the planet shifts direction from east to west or west to east. These points are the 'station' points, because for a day or two Mars is standing still. When Mars is within the loop, running westward, he is nearest to Earth and largest in angular size. In space, this part of the loop is actually closer to Earth, like looking at a turntable from its side. The leads to and from the loop are farther away. Mars outside the loop is much dimmer and smaller.
Mars in 2008-2011 --------------- Altho this article is written in January 2010, the tables here give the principal events for the entire circuit of Mars from the previous conjunction with the Sun to the next. This gives a complete view of the behavior of the planet. Dates and hours are jimmied for the best view from New York. Dawn events are in the east toward the sunrise point; dusk, west, sunset point. You may better understand the movement of Mars by watching two days before the event date thru two days after it. -------------------------- NYC date | hour | event ------------+------+--------------------- 2008 Dec 5 | -- | conjunction with Sun 2009 Jan 5 | dawn | emerges from dawn, start of apparition 2009 Jan 27 | dawn | 4 deg S of Mercury 2009 Feb 17 | dawn | 1 deg S of Jupiter 2009 Mar 3 | dawn | 1 deg N of Mercury 2009 Apr 21 | dark | 6 deg S of Venus 2009 Apr 20 | -- | perihelion, 1.38146 AU Sun 2009 Apr 21 | dark | 4 deg S of Venus 2009 Jun 21 | dark | 2 deg N of Venus 2009 Jul 12 | dark | 5 deg S of Alcyone 2009 Jul 26 | dark | 4 deg N of Aldebaran 2009 Aug 12 | -- | increase to +1.0 magnitude 2009 Aug 20 | -- | ascending node, north of ecliptic 2009 Oct 7 | dark | 6 deg S of Pollux 2009 Oct 24 | -- | increase to +0.5 magnitude 2009 Oct 27 | -- | vernal equinox, northern spring begins 2009 Oct 29 | -- | west square, magn +0.5, diam 7.8sec 2009 Nov 1 | dark | inside Beehive cluster 2009 Nov 26 | -- | increase to +0.0 magnitude 2009 Dec 19 | -- | increase to -0.5 magnitude 2009 Dec 20 | -- | begins retrograde westward in Cancer 2009 Jan 9 | -- | increase to -1.0 magnitude 2010 Jan 27 | -- | proximity, 0.66399 AU, 99.33 million km 2010 Jan 29 | -- | opposition, 0.66456 AU, mag -1.3, diam 14.1sec 2010 Feb 5 | dark | 3 deg N of Beehive cluster 2010 Feb 17 | -- | decrease to -1.0 magnitude 2010 Mar 4 | -- | decrease to -0.5 magnitude 2010 Mar 11 | -- | resumes prograde eastward in Cancer 2010 Mar 23 | -- | decrease to -0.0 magnitude 2010 Mar 29 | -- | apohelion, 1.66594 AU Sun, 1.00674 AU Earth 2010 Apr 15 | -- | decrease to +0.5 magnitude 2010 Apr 17 | dark | 1 deg N of Beehive cluster 2010 May 4 | -- | east square, magn +0.8, diam 7.1sec 2010 May 18 | -- | decrease to +1.0 magnitude 2010 Jun 7 | dark | 1 deg N of Regulus 2010 Jul 23 | -- | decrease to +1.5 magnitude 2010 Jul 30 | dark | 2 deg S of Saturn)-convention Venus-Saturn 2010 Aug 19 | dark | 2 deg N pf Venus ) 2010 Sep 6 | dark | 2 deg N of Spica)-convention Spica-Venus 2010 Oct 6 | dusk | 6 deg N of Venus) 2010 Oct 1 | -- | in dusk, sets at nightfall 2010 Nov 11 | dusk | 4 deg N of Antares 2010 Nov 13 | -- | autumnal equinox, northern fall begins 2010 Nov 21 | dusk | 2 deg N of Mercury 2010 Dec 12 | dusk | 1 deg S of Mercury 2010 Jan 9 | -- | immerges into dusk, end of apparition 2011 Feb 9 | -- | conjunction with Sun ----------------------------------------------------- For the most part, telescopic viewing of Mars pretty much ends when he reaches the east square, standing 90 degrees east of the Sun. He fades slowly there after and is far less prominent among the stars. In spite of this waning luster, Mars configures with Venus and Saturn and then with Spica and Venus in fall 2010 for a last hurrah.
Mars and the Moon --------------- The table below gives the conjunctions of Mars with the Moon. Because the Moon moves so swiftly thru the stars, the conjunction can unravel on the previous or next day and can even be loose on the event day as seen from New York. The age, elongation, and offset to Mars are for the actual conjunction, and can only approximate the situation when the pair is visible from New York many hours away. ----------------------------------------- NYC date | hour | Mars | Age | Elong | Phase ------------+------+------+------+-------+------ 2008 Dec 26 | dawn | 5d S | 29.1 | 6 W } new Moon 2009 Jan 24 | dawn | 4d S*| 28.5 | 15 W | waning crescent 2009 Feb 23 | dawn | 6d S | 27.8 | 21 W | | 2009 Mar 24 | dawn | 4d S | 27.3 | 23 W | | 2009 Apr 22 | dawn | 6d S | 26.9 | 32 W | | 2009 May 21 | dark | 7d S | 26.5 | 38 W | | 2009 Jun 19 | dark | 6d S | 26.0 | 44 W | | 2009 Jul 18 | dark | 5d S | 25.3 | 58 W | | 2009 Aug 16 | dark | 3d S | 24.6 | 60 W | \|/ 2009 Sep 12 | dark | 1d S | 23.9 | 69 W | ------- 2009 Oct 12 | dark | 1d N*| 22.8 | 92 W | 3rd quarter 2009 Nov 9 | dark | 3d N | 21.8 | 98 W | 3rd quarter 2009 Dec 6 | dark | 5d N | 19.9 | 113 W | waning gibbous 2010 Jan 2 | dark | 7d N | 17.6 | 145 W | waning gibbous 2010 Jan 29 | dark | 7d N | 14.8 | 179 E | full Moon 2010 feb 25 | dark | 5d N | 11.8 | 146 E | waxing gibbous 2010 Mar 24 | dark | 5d N | 9.6 | 117 E | waxing gibbous 2010 Apr 21 | dark | 5d N | 8.0 | 97 E | 1st quarter 2010 May 19 | dark | 5d N | 6.7 | 81 E | 1st quarter 2010 Jun 16 | dark | 6d N | 5.6 | 68 E | waxing crescent 2010 Jul 15 | dark | 6d N | 4.8 | 58 E | | 2010 Aug 12 | dark | 6d N | 3.9 | 48 E | | 2010 Sep 10 | dusk | 5d N | 3.2 | 40 E | | 2010 Oct 9 | dusk | 4d N | 2.5 | 31 E | | 2010 Nov 7 | dusk | 2d N | 1.8 | 22 E | \|/ 2010 Dec 6 | dusk | 1d S*| 1.4 | 15 E | ------- 2011 Jan 4 | dusk | 5d S | 0.7 | 8 E | new Moon 2011 Feb 2 | dusk | 7d S | 0.1 | 0 E | new Moon ------------------------------------------------------ The starred entries under 'Mars' are instances where the Moon passes right over the planet for a rare occultation. None of these is observable from New York because they occur when the Moon is down. We must be satisfied with only an approach or reproach of the tow bodies. It is a happy feature that the current apparition starts and ends with such a hiding behind the Moon! As a practical matter conjunction with the Moon can't be seen well at all until the elongation is about 20 east or west of the Sun and the ecliptic is inclined steeply to the local horizon to get the Moon to higher altitude and darker twilight.
Other attractions --------------- About halfway between Castor-Pollux and Regulus is the Beehive star cluster. This is in downtown Cancer, a constellation of dim stars usually missed in a sky with luminous graffiti. This cluster is about 2 degrees across and appears as a misty spot in dark skies. In binoculars the Beehive resolves into a couple dozen stars. The group is about 590 lightyears away. Mars retrograde loop circulates among three bright planetary stars! Pollux, Algieba (gamma Leonis) and rho1 Cancri have their own planets. rho1 Cancri needs binoculars to see well while Pollux and Algieba are naked-eye targets. You will not, of course, see the planets, but the fact you can see the stars induces a wonder if the folk up there are gazing back at us. Castor is the closest system of SIX stars. It stands 52 lightyears away and has three pairs of stars. Two pairs are close together to combine their light into the Castor you see in the sky. The third pair is very dim with no contribution to the luster of Castor. Binoculars show Castor only as a single point with no hint of its detail.
Conclusion -------- Oppositions of Mars are exciting events to watch, even if you don't got a telescope. In fact, for this 2010 round, a telescope may present you with a poorly defined pink dot. Yet to the eye and binoculars Mars is a brilliant visitor in Cancer, gyrating thru his retrograde loop. Later in 2010 he jives with other planets on his way into twilight around the Sun.