Mars
JPL orbital parameters (1.5237 AU, 686.98 d), 780-day synodic opposition cycle, 25.1″ maximum disk, and telescope observing guide for Mars.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Peak perihelic opposition magnitude (V) | -2.94 mag | -2.94 to 1.86 mag | JPL ephemeris photometry (swings by 4.8 magnitudes between perihelic opposition and aphelic conjunction) | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Orbital semi-major axis | 1.52368 AU | ± 0.00001 AU | JPL DE441 planetary ephemeris (eccentricity e = 0.0934) | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Sidereal orbital period | 686.98 d | ± 0.01 d | JPL DE441 ephemeris (1.8808 Julian years; synodic opposition period = 779.94 d) | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Planetary mass | 0.10745 M⊕ | ± 0.00001 M⊕ | Spacecraft tracking (6.4171 × 10^23 kg) | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mean volumetric radius | 0.532 R⊕ | ± 0.001 R⊕ | MOLA laser altimetry (3,389.5 km) | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Apparent diameter at opposition | 0.418 arcmin | 0.058 to 0.418 arcmin | Ranges from 3.5″ at conjunction to 13.8″ at aphelic opposition and 25.1″ at perihelic opposition | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Mars (Terrestrial Planet & Opposition Cycle) at RA 04h 30m 00.00s, Dec +22° 00′ 00.0″ within Ecliptic (Zodiac), alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Mars, the fourth planet from the Sun and the outermost of the four rocky terrestrial planets, has a diameter of 6,779 kilometers (0.532 Earth radii) and a mass of 0.107 Earth masses, giving it a surface gravity 38% of Earth's. In 1609 Johannes Kepler used Tycho Brahe's 20-year compilation of naked-eye positional measurements of Mars to prove that planetary orbits are ellipses rather than circles—discovering Kepler's first two laws of planetary motion solely because Mars's high orbital eccentricity (e = 0.0934) produced an 8-arcminute discrepancy from circular models.
Mars rotates on its axis in 24 hours 37 minutes 22.7 seconds (a Martian 'sol')—only 41 minutes longer than Earth's day—and has an axial obliquity of 25.19° (compared to Earth's 23.44°), making it the only planet whose solid surface features, dark basaltic albedo markings, and waxing/waning seasonal water-and-CO2 polar ice caps can be watched directly in backyard telescopes.
Although today's Martian atmosphere is a cold, thin carbon dioxide envelope with a mean surface pressure of just 6.1 millibars (~0.6% of Earth's sea-level pressure), orbital spectroscopy and rovers (Spirit, Opportunity, Curiosity, and Perseverance) have proved that early Noachian Mars (~3.7–4.1 billion years ago) hosted deep crater lakes, branching river deltas, and phyllosilicate clays.
Practical Visual Observing Guide
- Mars reaches opposition only once every 780 days (2 years and 50 days)—the longest synodic interval of any major planet—so telescopic observing windows last only ~3 to 4 months around each opposition.
- In a 100–200 mm telescope at 180×–300× during the months around opposition, look for the brilliant white North or South Polar Cap (and dark melt band), triangular dark Syrtis Major, Sinus Sabaeus, Mare Acidalium, and bright Hellas Basin.
- Because Mars's solar day is 24h 37m, observing at the same clock hour on consecutive nights shifts Martian surface longitudes backward by ~9° per night, letting you map the entire globe over a 40-day cycle.
Catalog Cross-Identifications & Aliases
Common Aliases: The Red Planet · Sol IV
| Catalog Authority | Identifier |
|---|---|
| WIKIDATA | Q111 |
Related Objects, Comparisons & Guides
Jupiter (Gas Giant & Galilean Moons)
JPL orbital parameters (5.2038 AU, 11.862 yr), opposition magnitude −2.94, 50.1″ angular disk, Galilean moons, and observing guide for Jupiter.
Saturn (Ringed Giant & Cassini Division)
JPL orbital parameters (9.5826 AU, 29.457 yr), ring tilt cycle, Cassini Division resolution, and telescope observing guide for Saturn.
Aldebaran (Alpha Tauri Orange Giant)
Coordinates, Hipparcos distance (66.6 ly), 45.1 R☉ radius, Hyades foreground alignment, and observing guide for Aldebaran in Taurus.
Betelgeuse (Alpha Orionis Red Supergiant)
Coordinates, competing optical vs radio distances (168 vs 222 pc), radius, Great Dimming physics, and observing guide for Betelgeuse.
Solar System Planets & Moons Opposition Guide
How to observe Jupiter, Saturn, Mars, Titan, and Europa around opposition using high magnification, atmospheric dispersion control, and transit timing.
Suburban & Urban Light-Pollution Targets Guide
Practical observing guide to high-surface-brightness targets—planets, double stars, open clusters, and planetary nebulae—that cut through Bortle 6–8 skyglow.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Scientific Sources & Dataset Provenance
- NASA/JPL Solar System Dynamics & Planetary Fact Sheets (DE441 (2021/2026)): Park, R. S., et al. 2021, AJ, 161, 105 (The JPL Planetary and Lunar Ephemerides DE440 and DE441) — NASA Jet Propulsion Laboratory / GSFC