Description
Convert a proleptic Gregorian date and uniform-day seconds to fractional Julian day.
Geodesy distinguishes a mathematical reference ellipsoid, a realized coordinate datum and the physical gravity field. Geodetic latitude follows the ellipsoid normal; geocentric latitude follows a radius from the center. Ellipsoidal height, orthometric height and geoid undulation are separate signed quantities. Keep the declared ellipsoid, coordinate axes, angular units and time scale with a result.
Convert a proleptic Gregorian date and uniform-day seconds to fractional Julian day.
A Julian date has a noon-based day origin, so midnight dates end in a half day. This calendar arithmetic must remain separate from the choice or conversion of physical time scale.1
When to use this tool
Use this tool when you need to convert a proleptic Gregorian date and uniform-day seconds to fractional Julian day.
How to use the tool and how it works
- Enter gregorianDate, secondsSinceMidnight using the definitions below.
- Run the operation. Resolve input-format errors before interpreting an output.
- Read result.julianDay, using the stated boundary, ordering, sign and absence conventions.
Validate an exact YYYY-MM-DD proleptic Gregorian date, compute its integer Julian day number, then subtract 0.5 and add secondsSinceMidnight/86,400.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| gregorianDate | Exact proleptic Gregorian YYYY-MM-DD date with year 0001–9999 and a valid month/day. | Text, at most 8,192 UTF-16 code units; narrower grammar/range rules also apply. |
| secondsSinceMidnight | Seconds on the supplied calendar day, from zero up to but excluding 86,400. | Finite numeric value satisfying the stated comparisons. |
| Output field | Interpretation |
|---|---|
| result | Object containing the fields below. |
| result.julianDay | Proleptic Gregorian date/time as Julian day, including fraction. |
{
"input": {
"gregorianDate": "2000-01-01",
"secondsSinceMidnight": 43200
},
"output": {
"result": {
"julianDay": 2451545
}
}
}Limitations and assumptions
- Years are 0001–9999 and seconds in [0,86,400). Calendar validation includes Gregorian leap years; no local time zone, Julian-calendar switchover or UTC leap-second parsing is included. The supplied time scale is retained.
- All quantities are finite and retain the units stated for this operation. Ellipsoid-parameter tools use semi-major axis 1–10⁸ m and dimensionless flattening 0–0.02; explicit-axis tools use 0.9a≤b≤a unless a tighter bound is stated. These tools do not fetch datums, geoid grids, satellite observations or Earth-orientation updates.
- Every declared outer field is required and unknown outer fields are rejected. Strings and JSON text have size limits, lists are bounded to 128 entries, and JSON nesting/node counts are bounded. Tighter operation-specific bounds stated above take precedence.
- Numeric results must be finite. Large physical magnitudes are allowed by the output evidence checks, while integer fields and source schemas retain their exactness rules. Source indexes are zero-based. Floating-point residues can remain even where an ideal formula gives an exact zero.
Alternative or Complementary methods
Use a coordinate transform for a change of representation and explicit datum parameters for a change of reference frame. Preserve model and convergence metadata, and use observation and datum information appropriate to a real survey before interpreting a computed tolerance as accuracy.
References
-
Converting between Julian dates and Gregorian calendar dates — U.S. Naval Observatory
-
Tool behavior and example: Julian Date from Calendar Date Standard Converter — tool.io
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