Solar day unknown: Titan, Europa. No admitted heliocentric period: Moon, Titan, Europa. No parent year or satellite orbit substituted.
Rotation is one turn relative to the stars; solar day is the mean Sun-to-Sun cycle. A year uses Atlas’s two-body heliocentric period. Select a value for its resolved record and provenance.
The solar-day CSV stays in evidence; the full dataset CSV includes all three series.
Values / method / sources
Mean solar day ranking
Mercury has the longest mean solar day: 4,223 hours. Jupiter has the shortest mean solar day: 9.926 hours.
Titan and Europa have no published mean solar day and are shown without a rank.
Values and sources
Mean solar days · Earth reference
Every row keeps its reference level, resolution state, and source attached. Derived means Atlas calculated the value from published inputs with a registered formula.
Published comparison values. Day length is shown in hours; ratios use Earth as the reference. Shared ranks use the stored comparison tolerance.
Rank
World
Value
vs. Earth
Reference level
State
Evidence
1Rank 1
MercuryReference
4,223 hours
176×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Mercury
Source passport: Mercury
Published value
4,223 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: 1,408 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Mercury Fact Sheet (2024-02-04 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Mercury Fact Sheet. Archived 2024-02-04; retrieved 2026-09-02.Locator: Mercury/Earth comparison table, Length of day: Mercury 4222.6 hRetrieved 2026-09-02 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Mercury row, Sidereal Rotation Period: 58.6462 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
2Rank 2
VenusReference
2,802 hours
117×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Venus
Source passport: Venus
Published value
2,802 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: -5,832 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Venus Fact Sheet (2024-02-04 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Venus Fact Sheet. Archived 2024-02-04; retrieved 2026-09-02.Locator: Venus/Earth comparison table, Length of day: Venus 2802.0 hRetrieved 2026-09-02 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Venus row, Sidereal Rotation Period: -243.018 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
3Rank 3
MoonReference
708.7 hours
29.5×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Moon
Source passport: Moon
Published value
708.7 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: 655.7 hoursNASA Goddard Space Flight Center National Space Science Data CenterShared provenance — at least one underlying source also supports the comparison value.
Sources
Moon Fact Sheet (2024-10-03 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Moon Fact Sheet. Archived 2024-10-03; retrieved 2026-08-30.Locator: Moon/Earth comparison table, Sidereal rotation period: Moon 655.720 h; Moon/Earth comparison table, Synodic period: Moon 29.53 dRetrieved 2026-08-30 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. The companion fact-sheet notes define surface acceleration as rotation-inclusive.
4Rank 4
PlutoReference
153.3 hours
6.39×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Pluto
Source passport: Pluto
Published value
153.3 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: -153.3 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Pluto Fact Sheet (2024-02-04 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Pluto Fact Sheet. Archived 2024-02-04; retrieved 2026-09-02.Locator: Pluto/Earth comparison table, Length of day: Pluto 153.2820 hRetrieved 2026-09-02 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Pluto row, Sidereal Rotation Period: -6.3872 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
5Rank 5
MarsReference
24.66 hours
1.03×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Mars
Source passport: Mars
Published value
24.66 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: 24.62 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Mars Fact Sheet (2024-09-15 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Mars Fact Sheet. Archived 2024-09-15; retrieved 2026-08-30.Locator: Mars/Earth comparison table, Length of day: Mars 24.6597 hRetrieved 2026-08-30 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Mars row, Sidereal Rotation Period: 1.02595676 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
6Rank 6
EarthDefault baselineReference
24.00 hours
1×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Earth
Source passport: Earth
Published value
24.00 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: 23.93 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Earth Fact Sheet (2024-11-16 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Earth Fact Sheet. Archived 2024-11-16; retrieved 2026-09-02.Locator: Earth Fact Sheet, Orbital parameters, Length of day: 24.0000 hRetrieved 2026-09-02 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Earth row, Sidereal Rotation Period: 0.99726968 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
7Rank 7
UranusReference
17.24 hours
0.718×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Uranus
Source passport: Uranus
Published value
17.24 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: -17.24 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Uranus Fact Sheet (2024-10-07 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Uranus Fact Sheet. Archived 2024-10-07; retrieved 2026-08-30.Locator: Uranus/Earth comparison table, Length of day: Uranus 17.24 hRetrieved 2026-08-30 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Uranus row, Sidereal Rotation Period: -0.71833 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
8Rank 8
NeptuneReference
16.11 hours
0.671×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Neptune
Source passport: Neptune
Published value
16.11 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: 16.11 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Neptune Fact Sheet (2024-10-06 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Neptune Fact Sheet. Archived 2024-10-06; retrieved 2026-08-30.Locator: Neptune/Earth comparison table, Length of day: Neptune 16.11 hRetrieved 2026-08-30 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Neptune row, Sidereal Rotation Period: 0.67125 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
9Rank 9
SaturnReference
10.66 hours
0.444×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Saturn
Source passport: Saturn
Published value
10.66 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: 10.66 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Saturn Fact Sheet (2024-10-04 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Saturn Fact Sheet. Archived 2024-10-04; retrieved 2026-08-30.Locator: Saturn/Earth comparison table, Length of day: Saturn 10.656 hRetrieved 2026-08-30 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Saturn row, Sidereal Rotation Period: 0.44401 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
10Rank 10
JupiterReference
9.926 hours
0.414×
Not applicable
Settled
Source passportSettledNASA Goddard Space Flight Center National Space Science Data Center for Jupiter
Source passport: Jupiter
Published value
9.926 hours
Primary source
NASA Goddard Space Flight Center National Space Science Data Center
Definition
mean solar day: the average interval from one local solar transit to the next
sidereal rotation period, signed so that a negative value records retrograde rotation: 9.925 hoursNASA Jet Propulsion Laboratory Solar System DynamicsIndependent provenance — the underlying source sets do not overlap.
Sources
Jupiter Fact Sheet (2024-10-04 NASA NSSDC archive capture)NASA Goddard Space Flight Center National Space Science Data CenterNASA NSSDC. Jupiter Fact Sheet. Archived 2024-10-04; retrieved 2026-09-02.Locator: Jupiter/Earth comparison table, Length of day: Jupiter 9.9259 hRetrieved 2026-09-02 · published Not statedTier B · us-government-work · reuse allowedThe live NSSDC host was unavailable during review, so Atlas cites a dated, immutable capture transparently. Each candidate locator transcribes the cited field's label, value, and unit.
Planetary Physical ParametersNASA Jet Propulsion Laboratory Solar System DynamicsJPL Solar System Dynamics. Planetary Physical Parameters. NASA Jet Propulsion Laboratory. Retrieved 2026-08-30.Locator: Planet table, Jupiter row, Sidereal Rotation Period: 0.41354 dRetrieved 2026-08-30 · published Not statedTier A · us-government-work · reuse allowedNumerical facts are retained with NASA/JPL credit; linked third-party references keep their own terms.
—
TitanReference
Not established
—
Not applicable
Not established
Source passportNot establishedNo admissible source for Titan
Source passport: Titan
Canonical value
Not established
Canonical source
No admissible source
Definition
mean solar day: the average interval from one local solar transit to the next
Reference level
Not applicable
Epoch
Not tied to a stated epoch
Resolution state
Not established
Provenance details
Uncertainty
Not stated
Alternatives
No competing admissible value
Value ID
titan:day_length:mean_solar_day:unknown:0
Dataset version
0.1
Related context
sidereal rotation period, signed so that a negative value records retrograde rotation: 382.7 hoursInternational Astronomical Union Working Group on Cartographic Coordinates and Rotational ElementsProvenance relationship not established.
Related context sources
Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015International Astronomical Union Working Group on Cartographic Coordinates and Rotational ElementsArchinal, B. A., et al. (2018). Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015. Celestial Mechanics and Dynamical Astronomy, 130, 22. https://doi.org/10.1007/s10569-017-9805-5Locator: Saturn VI Titan rotational elements: W = 186.5855° + 22.5769768° dRetrieved 2026-08-30 · published 2018-01-17Tier A · facts-with-citation · reuse allowedAtlas retains cited reference radii and rotational constants only; the report and its typography remain under their upstream terms.
—
EuropaReference
Not established
—
Not applicable
Not established
Source passportNot establishedNo admissible source for Europa
Source passport: Europa
Canonical value
Not established
Canonical source
No admissible source
Definition
mean solar day: the average interval from one local solar transit to the next
Reference level
Not applicable
Epoch
Not tied to a stated epoch
Resolution state
Not established
Provenance details
Uncertainty
Not stated
Alternatives
No competing admissible value
Value ID
europa:day_length:mean_solar_day:unknown:0
Dataset version
0.1
Related context
sidereal rotation period, signed so that a negative value records retrograde rotation: 85.23 hoursInternational Astronomical Union Working Group on Cartographic Coordinates and Rotational ElementsProvenance relationship not established.
Related context sources
Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015International Astronomical Union Working Group on Cartographic Coordinates and Rotational ElementsArchinal, B. A., et al. (2018). Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015. Celestial Mechanics and Dynamical Astronomy, 130, 22. https://doi.org/10.1007/s10569-017-9805-5Locator: Jupiter II Europa rotational elements: W = 36.022° + 101.3747235° d plus periodic termsRetrieved 2026-08-30 · published 2018-01-17Tier A · facts-with-citation · reuse allowedAtlas retains cited reference radii and rotational constants only; the report and its typography remain under their upstream terms.
Why the result changes
Why this order?
A mean solar day is the average interval from one local noon to the next. It can differ sharply from sidereal rotation because a world moves along its orbit while it turns.
Mean solar days set the ranking. Titan and Europa remain visible without a rank; the Sun has no single comparable day because it rotates differentially.
The longest days belong to Mercury, then Venus.
Definition and evidence
What this comparison means.
Definitions
mean solar day: the average interval from one local solar transit to the next
Sidereal rotation stays visible in each passport. Retrograde rotation carries a minus sign there; ranked solar days stay positive. Mercury's slow turn and fast orbit stretch its solar day far beyond one rotation. For Saturn and Neptune, small physical differences are lost at the sources' published precision, so their displayed solar and sidereal values can appear tied or reversed.
Resolution states
Settled
Admissible values agree.
Derived
Calculated from published inputs.
Contested
Admissible values disagree.
Not established
No admissible value fits the definition.
Identity marks—not to scale
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Moon
Titan
Europa
Pluto
Credit: Blue Marble, March 2014 — NASA/GSFC; Europa full disk, Galileo — NASA/JPL; Full Moon — NASA/GSFC; High-resolution Jupiter globe — NASA/JPL/University of Arizona; Mars global mosaic — NASA/USGS; Mercury globe — NASA/JHUAPL/Carnegie Institution of Washington; Neptune, Voyager 2 — NASA/JPL; Pluto color view — NASA/JHUAPL/SwRI; Saturn, Cassini — NASA/JPL/Space Science Institute; Titan natural-color composite, Cassini — NASA/JPL/Space Science Institute; Uranus, Voyager 2 — NASA/JPL-Caltech; Venus radar-data globe — NASA/JPL
Yale Thomas. Atlas of Worlds. “Days / years: rotation, solar day and heliocentric year” View: default. Dataset 0.1. https://yalethom.as/worlds/day-length/. Accessed [the date you viewed this page].
Replace the bracketed access-date instruction with the date you viewed this page.
Download the table
Includes stable body, role, definition, value, provenance, version, attribution, and license fields in display order.
