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(Updated Aug. 5, 2008)
Mars24 is a cross-platform Java application which displays a Mars "sunclock", a graphical representation of Mars showing the current day- and nightsides of Mars, along with numerical readouts of the time in 24-hour format. Other displays include a plot showing the relative orbital positions of the four inner planets, a panorama showing the solar path as seen from a given location on Mars, and the Mars analemma.
Mars24 cannot accurately determine the time on Mars unless your computer's time, time zone and date are set correctly.
Please read the accompanying Technical Notes on Mars Solar Time for a more detailed discussion about the meaning of the various display values and for definition of Mars time units.
When first launched, Mars24 displays three windows: a settings window for controlling display options, a small display window showing the time on Mars and on Earth, and a large display window which can show either 1) a sunclock map of Mars, 2) an orbital positions plot, 3) a local panorama plot for a location on Mars, or 4) the Mars analemma. If you close a window, you can make it visible again using the appropriate command in the Window menu. The Window menu also allows you to display the help pages.
Many computers allow you to quit an application by closing all its open windows. However, if you wish Mars24 to use your same window configuration (size and placement on the screen), you must instead use the "Quit" command in the menus. If you are using a Macintosh computer, you must always use the Quit command when you are done.
When you quit Mars24, it saves the settings of the various controls to a preferences file, The next time you use the program, it will open that preferences file and initialize the controls using the prefs it finds.
If you are using Mars24 on a Windows computer, you must use the "Quit" item in the File menu if you Mars24 to remember exactly which program windows were open and to show them the next time you launch the program.
If you would like to save several different configurations of the controls, you can use the Open and Save Settings commands in Mars24's File menu to do so. Saved prefs files must be given the extension .m24. A few sample prefs files are included with Mars24. (Macintosh users: if you doubleclick on a .m24 prefs file, Mars24 should automatically open it.)
This "Mars24 Settings" window is divided into three tabbed panels: one tab allows you to specify how to set the display time for both Earth and Mars, the second to specify properties of the large graphical display, and the third a few general options.
We'll start by taking a look at the third tab, which is labeled "Gen'l", for "general". This set of controls includes three pop-up menus for general settings which you are likely to set and then rarely change.
The first pop-up offers a choice of longitude-latitude coordinate systems. The two choices are "planetocentric" and "planetographic". These are two schemes for specifying the location of a spot on a planet's surface used by planetary scientists, and because both systems are used (by different research groups), we offer the choice in Mars24. The most obvious difference between thse coordinates is that in the p'centric system, longitude values are specified with positive values meaning east of the prime meridian and negative values west of the meridian. Conversely, positive longitude values in p'graphic coordinates are west of the prime meridian. Thus, 45° p'centric equals -45° p'graphic. There difference between latitudes in p'centric vs. p'graphic coordinates is more complex and depend on whether latitude is measured as the angle of arc from the equatorial plane (p'centric) or reference to the line normal (perpendicular) to the mean surface (p'graphic). The difference between latitude values is greatest for planets which are highly oblate (non-sperical), such as Jupiter and Saturn, but even on Mars it can be as much as 0.3° degrees at ±45° latitude.
The second pop-up in the general settings tab is the font which you would like used in all the display read-outs. The choices will be limited to those fonts on your computer which Mars24 had determined are monospaced, i.e., all letters and numbers are of equal width. We have found that Andale Mono, Lucida Console, Monaco, and OCR A Std (if available) all look good.
The third pop-up is a choice of default file format to use whenever you decide to save a copy of the image in one of the two displays. The choices are GIF and PNG for bitmap images, and PDF and Postscript (PS) for vector art. However, when you do save an image, you can always opt to specify a different format at that time.
The Earth time settings in the first tabbed panel gives you four choices for specifying what time on Earth should be used in making all the various calculations that Mars24 must perform, both in determining the Mars time and generating the displays.
The first (default) Earth time choice is to use the current time, i.e., now, whenever "now" happens to be.
The second choice is to add some offset to the current time on Earth. For example, if you need information about the time on Mars exactly 100 Earth hours from now, you would select this option and enter "100" in the hours field. Note that when you select this option, the clocks in the time display keep on ticking, but are just offset from the current time by whatever amount have entered.
To find out the time on Mars that corresponds to a specific Earth time, you would select the third choice and enter a time of day in the first input field and a date in the second field. The time and date must be in UT (Universal Time), which is in everyday usage effectively the same as Greenwich Mean Time. Please note that the Java routine which we use to parse the date entry is a little finicky about the format of the entered date.
The fourth and final option for choosing what Earth time should be displayed is specification of the Julian Date (JD). This is the number of days that have passed since noon on Jan. 1, 4713 BCE. This count is a very useful value in astronomy and is often used to indicate the dates of astronomical events and observations, especially those which predate use of the modern Gregorian calendar. Because the Julian Date for modern dates is a relatively large and unwieldy number, your input here should instead be of the easier-to-use Modified Julian Date, the number of days since midnight starting Nov. 17, 1858.
Also in the Earth time settings is a checkbox which allows you to specify how you would like Earth date shown in the display windows. Normally it is shown in ISO format, i.e., "YYYY-MM-DD", but if you opt to show the date as day-of-year (a scheme that planetary mission controllers often use) then the format changes to "YYYY-DDD".
And last in the Earth time settings is a menu listing a choice of distance units. The distnace in question is that between Earth and Mars, and the choices are in kilometers (actually mega-kilometers), astronomical units, and light time.
The Mars time settings effectively gives you two choices, to either display the local time for some particular place on Mars or to display the mission time for one of the current lander projects. If you choose the first option, you also need to select a time format. When Mars24 is first launched, the default is to display the Local Mean Solar Time on the Mars prime meridian.
For example, if you would like to display the time at a Olympus Mons, you would click the "local time" radio button and enter into the location fields longitude 133.10°W and latitude 18.60°N.1 (Actually, the N-S latitude doesn't matter when calculating the time, so you could just leave the latitude field at 0°N.) The adjacent format menu gives you the option of displaying the time in either Local Mean Solar Time (LMST), Local True Solar Time (LTST), or local mean zonal time (MTC+N). Zonal time is marked by a suffix indicating the time zone, e.g., "MTC-2" identifies the time zone two hours behind (west of) the prime meridian. (See the "Notes about Mars Time" help page for further information about these formats.).
The alternative Mars time setting is to display the mission time for the current lander missions, i.e., MER-A Spirit, MER-B Opportunity, and Mars Phoenix. The mission time is shown as a time of day and a Sol value. The latter is the count of the number of Martian days since landing. For MER-A and MER-B, "Sol 1" is defined as the Martian solar day on which the lander touched down, and the day before landing was "Sol -1". For Phoenix, mission planners specified touchdown day as "Sol 0". The time of day displayed for each mission is offset from the Local Mean Solar Time at each individual landing site. The difference from LMST is the result of decisions made during mission planning. See the "Notes about Mars Time" help page or the FAQ for further detail on the offset amounts. (If you are displaying the time for an Earth date prior to landing, the time of day will instead read either "Not Launched" or "In Flight".)
We'll come back to discussing the plot settings tab below when we discuss the graphic display window.
This window is divided into four quarters, grouped two above and two below. Let's take a look at the bottom two first.
The most prominent items in the bottom two quarters of the time display are the Earth time readouts, at left in UTC (Coordinated Universal Time) and at right in the user's local time zone, according to the choice selected in the Earth time settings. Below each of these is the corresponding date. Remember, both UTC and local time (and consequently the time on Mars) will not be correct unless your computer's time and time zone have been set correctly.
At left, below the Earth UTC time and date is the corresponding Modified Julian Date (MJD), which was described above.
At right, below the user's local time and date is the distance between Earth and Mars. If you have chosen light minutes or light seconds in the distance units menu, the value shown here is the one-way light time (OWLT), i.e., the amount of time a photon would take to traverse the distance between the two planets. Depending on the current relative orbital positions of the two planets, this value ranges between 3 and 22 minutes.
In the upper half of the time display window are the Mars time read-outs. If you have selected the default choice in the settings, then just as for Earth the top left will show the "standard Mars time" and the top right a local time. The latter is determined by the location you specified in the Mars time settings.
The "standard Mars time" is given using the designation "MTC", or Coordinated Mars Time. In analogy to Earth's UTC, this is the Local Mean Solar Time at Mars' prime meridian, which is defined by the location of the crater Airy-0.
As we noted above, the local Mars Time readout is given for a specific longitude and latitude and uses one of three different time formats which you may choose from in the settings. The lon-lat chosen is shown immediately below the local time.
The upper half of the time display window also contains a few other numeric readouts. At left, below the MTC, are three items giving some information about the Mars "date". At present, there is no recognized Mars calendar so these data are shown in an alternative fashion. First, in analogy to the Julian Date on Earth, there is a readout for MSD, or Mars Sol Date, i.e., a count of the Mars days — sols — that have elapsed since humans began to make useful observations of the surface features of Mars in the late 19th century. MSD 0.0 is approximately the same moment in time as MJD 5521.5 (noon on Dec. 29, 1873) on Earth.
Below the MSD is a readout of the Areocentric Solar Longitude, denoted (LS), the angle that Mars has reached in its orbit relative to vernal (spring) equinox in the northern hemisphere. Below the LS value is an indication of the corresponding Martian season. The abbreviation "NH" or "SH" which appears here stands for "northern hemisphere" or "southern hemisphere", as appropriate.
On the right side of the Mars time info, below the local time readout, are entries for the solar elevation and solar azimuth. For the location on Mars at which the local time is being calculated, these two values indicate the current position of the Sun, the elevation indicating its position above the horizon and the azimuth its position clockwise from due north.
The layout of the upper half of the time display, i.e., the sections displaying the time on Mars, will re-arrange itself if you have used the time settings to specify a mission time display. The only change in what is actually displayed is that the local time and solar position are replaced by the appropriate lander mission time and that the solar position is omitted.
The largest window displayed by Mars24 is the graphic display, which initially shows a sunclock of Mars. The other three types of plots which may shown in this window are an orbital position plot, a local panorama plot, and the Mars analemma. Use the menu at the top of the plot tab in the settings window to choose which of these to display.
The sunclock settings allow you to specify what map projection should be used to render the map, where that map should be centered, and what special markings should be drawn on the map.
The source map control allows you to choose between viewing a visually realistic map created for the National Geographic Society ("Mars_NGS_Map") or a color-coded altitude map ("Mars_MOLA_Topo"). Both were created by the Mars Global Surveyor project MOLA and MOC teams. The first of these maps is embedded in the Mars24 application; the second is in a directory called "sourcemaps". If you have other full global equirectangular maps of Mars, centered on the prime meridian, you can drop them into this directory and they will become available for Mars24 to use the next time you launch the program.
(When using the "NGS map", please keep in mind that this map came from a composite of Mars Global Surveyor imagery acquired during northern hemisphere winter, when the north polar ice cap was relatively large and the solar polar ice cap relatively small compared to their average extents. During southern hemisphere winter, the south polar cap becomes significantly larger, with a layer of frost extending almost all the way to the edge of Hellas Planitia.)
At start, Mars24 defaults to using an "orthographic" map projection, which if you are displaying the NGS map, renders a fairly realistic view of how Mars looks from space. The projection menu provides ten other choices, the two most popular of which are probably the equirectangular and Mollweide projections.
Next, you may choose the location on which the map projection should be centered. The controls allow you to select from a variety of landmarks, including a number of lander and geographic sites, or to specify a particular longitude and latitude. Alternatively, you can shift-click on the map itself, and the map will re-center at location where you clicked. (Note: Only the orthographic projection can be centered at a latitude off the equator.)
You can also specify "how dark" you would like the nightside of Mars shaded, with 100% meaning completely black and 0% no shading at all. A value of about 70% works well, but depending on your computer monitor you might find it helps to raise or lower this value a bit.
The next three lines of controls affect whether and how a longitude-latitude grid and the datum line should be drawn on the sunclock map. Although it looks a bit like a coastline, the datum line is really just the line of average altitude and has nothing to do with seas or oceans which may or may not have existed on Mars in the past.
The final set of options in the sunclock settings is a table of checkboxes indicating which, if any, of a set of locations should be marked on the map. The first two checkboxes are to mark the "Subsolar point" and the "Sub-Earth point", by a yellow circle and blue circle, respectively. The subsolar point is the location on Mars for which the Sun is directly overhead. Likewise, the sub-Earth point the location at which Earth is directly overhead, or for an observer on Earth looking at Mars, it is the spot directly in the middle of the hemisphere in view.
The next 11 points of interest in the table are lander sites, in order, the Mars Exploration Rover mission sites, the planned Mars Phoenix landing site, the three past successful landers (Viking 1 and 2 and Pathfinder), and five failed landers2. Following the landers in the table is a selection of notable surface features. The coordinates of all of the fixed locations are taken from the "marslandmarks.xml" file which is included in the Mars24 distribution and which Mars24 reads in when it first starts.
The second graphic display option is a plot of the orbital positions of the four inner planets: Mercury, Venus, Earth and Mars. Depending on how you have sized the plot window, part of Jupiter's orbit might also be visible. This plot has no special options which can be set using the controls in the prefs panel.
Mars's orbit is shown as a red ellipse and the planet's position is marked by a capital M, Earth is in light blue and marked by a capital E, Venus is in yellow and marked by a capital V, Mercury is in white and marked by a lower-case m, and Jupiter, if visible, is in orange and marked by a capital J. The orbits of the other planets beyond Mars are not shown because they are much too big to fit into the display window.
The other small markings on the orbital ellipses indicate the locations of perihelion, marked with a small p, and the northern hemisphere vernal (spring) equinox, marked ve. Perihelion is a planet's closest approach to the Sun; its aphelion, or farthest distance from the Sun, is indicated by an unlabeled tick mark on the far side of the orbital ellipse from perihihelion. Similarly, the start of the other seasons are indicated by unlabeled tick marks at 90° intervals from the vernal equinox tick.
You might find it interesting to use the Earth time settings to specify an Earth time and date in the morning of Aug. 27, 2003, and then examine the orbital positions plot. You'll see that Earth and Mars lie almost on the same line from the Sun, with Mars at its perihelion and Earth about 45° from its aphelion. This was the Great Mars Opposition of 2003, when Earth and Mars were the closest they had been in about 59,000 years. The light distance between the two planets on that date was just 3 minutes and 6 seconds. (Note: astronomical opposition was actually on Aug. 28, but because Earth and Mars orbit in slightly different planes, their closest approach was on Aug. 27.)
The panorama display shows the locations of the Sun and Earth in the sky, as seen from the location on Mars which you specified in the Mars time tab. The Sun is marked by a yellow circle and Earth by smaller blue circle. A grid is marked on the plot indicating the four cardinal directions.
Below the panorama is a table of numerical readouts which lists the times during the day of certain events related to the positions of the Sun and Earth. These include the time of highest ascent in the sky (for the Sun, that's true solar noon) and lowest descent (for the Sun, true midnight), plus the times of crossing the horizon (sunrise, sunset, Earthrise and Earthset).
If you specify that the location of the panorama is either the MER-A Spirit or MER-B Opportunity landing site, the plot will use a panorama photo taken by the appropriate lander as a backdrop. Otherwise it will use a solid Martian reddish color to represent the ground.
The first setting or the panorama display allows you to alter whether the panorama plot or the readout table is omitted from the display. This is useful if you want to draw the plot bigger or if you want to be able to see the entire readout table without scrolling.
The other settings for this display allow you to specify whether the Sun and Earth should be shown on the panorama plot as plain dots (yellow for the Sun, blue for Earth) or with their paths marked. The paths can be rendered as simple curves or as curves with tick marks. The ticks indicate where the Sun or Earth will be at intervals of one Mars-hour.
The determination of sunrise and sunset accounts for the fact that the Sun is not a pinpoint light source but has, on average, an apparent radius of 0.175° as seen from Mars. (It ranges from 0.193° at perihelion to 0.160° at aphelion.) Denoting sunrise as the time when the limb of the Sun reaches the horizon, then on average sunrise begins when the center of the Sun is 0.175° below the horizon.
Please note that the determination of times of sunrise, sunset, earthrise, and earthset does not adjust for any refraction of sunlight by Mars' atmosphere, nor is there any accounting for local topography at the location selected. Also note that the accuracy of the calculations of these event times will be improved if you specify correct planetographic latitude and longitude when you select the location for which you wish to see the panorama.
This diagram plots the Equation of Time (the difference between difference between the True Solar Time (TST) and the Mean Solar Time (MST)) and the solar declination as functions of the areocentric longitude, Ls. Or in other words, for a given position in Mars orbit, what are 1) the discrepancy between true solar noon and mean solar noon, and 2) the Sun's angle relative to the equatorial plane. The first of these is measured along the plot's x-axis and the second along the y-axis. The units of the x-axis are Mars minutes.
For example, on the first sol of Mars' northern hemisphere spring (Ls=0), you'll see that the solar declination is zero (exactly as it should be for an equinox) and that the discrepancy between true and mean solar time is a bit more than 41 minutes.
1. You can look up the coordinates of various features on Mars using the US Geological Survey's Gazetteer of Planetary Nomenclature's Mars page. Be sure to reference the index which uses planetographic latitude with west longitude.
2. Following is a roster of lander missions and a few notes about each. Again, all locations are in planetographic coordinates.
Active Landers (as of 2008-08-04):
MERA = Mars Exploration Rover A Spirit: NASA probe which landed Jan. 4, 2004, (UTC; late Jan. 3 in US time) at Columbia Memorial Station, in Gusev Crater, 175.48°E -14.75°N (p'centric) (image 1, image 2). Nominal mission duration was 90 sols (i.e., to Apr. 4, 2004), but as of Aug. 4, 2008, the rover was still in operation more than 1600 sols after landing.
MERB = Mars Exploration Rover B Opportunity: NASA probe which landed Jan. 25, 2004 at Challenger Memorial Station, in Meridiani Planum, 354.47°E -1.95°N (p'centric) (image 1, image 2). Nominal mission duration was 90 sols (i.e., to Apr. 25, 2004), but as of Aug. 4, 2008, the rover was still in operation more than 1600 sols after landing.
PHX
= Mars Phoenix:
NASA Mars Scout probe landed on Mars the late afternoon (U.S. time) of May 25, 2008.
The planned landing site was
in the Vastitas Borealis
at 233.98°E 68.15°N (p'centric)
(image 1
image 2).
Nominal mission period extends to late October 2008.
As of Aug. 5, 2008, the lander was in operation and in good health after 67
sols.
Planned Landers:
MSL =
Mars Science Laboratory:
The next rover mission should launch in autumn 2009 and land in summer 2010.
Its landing site site has not yet been decided. As of July 2008,
seven location were under consideration.
Past Successful Landers:
VIK1 = Viking 1 Lander: NASA probe which landed July 20, 1976, at Thomas Mutch Memorial Station, in Chryse Planitia, approx. 47.95°W 22.70°N (image 1, image 2). The Viking 1 lander was active until Nov. 13, 1982.
VIK2 = Viking 2 Lander: NASA probe which landed Sep. 3, 1976, at Gerald Soffen Memorial Station, in Utopia Planitia, approx. 225.72°W 48.27°N (image 1). The Viking 2 lander was active until Apr. 11, 1980.
MPF = Mars Pathfinder: NASA probe which landed July 4, 1997, at Carl Sagan Memorial Station, in Ares Vallis, approx. 33.25°W 19.47°N (image 1, image 2). The Mars Pathfinder lander was active until Sep. 27, 1997.
VIK and MPF coordinates are per Folkner et al. (1977), with longitude adjustment due to redefinition of prime meridian in Seidelman et al. (2002).
Unsuccessful Landers:
M2 = Mars 2 Lander: Soviet Union probe which crashed Nov. 27, 1971 in Hellas Planitia, 302°W 45°S. It was probably damaged by descent during a global dust storm. Its companion orbiter worked for several months.
M3 = Mars 3 Lander: Soviet Union probe which landed Dec. 2, 1971 in Terra Sirenum, 158°W 45°S. It began transmitting a test image on landing, but fell permanently silent 20 sec. later. It may have been damaged by descent during a global dust storm, or the dust storm may have caused a corona discharge. Its companion orbiter worked for several months.
M6 = Mars 6: Soviet Union probe which crashed Mar. 12, 1974 near Samara Valles, 19.42°W 23.90°S. A few minutes of descent data (unreadable due to a computer chip flaw) were transmitted, but transmissions ceased in "direct proximity to the surface".
MPL = Mars Polar Lander: American probe which apparently crashed Dec. 3, 1999, in the Planum Australae, at approx. 195.3°W 76.1°S. Failure is believed due to premature engine shutdown. MPL also carried two small Deep Space 2 microprobes to be dropped during =descent and which presumably impacted about 60 km away at approx. 196.5°W 75.0°S.
BEA = Beagle 2: ESA/British Mars Express probe which was to land Dec. 25, 2003 in Isidis Planitia (approx. 269.5°W 11.6°N). Communication with Beagle 2 was never established after it separated from the Mars Express orbiter. It was effectively declared lost on Feb. 11, 2004.