# `AstroUtils.Time`
[🔗](https://github.com/jakedjohnson/astro_utils/blob/v0.1.0/lib/astro_utils/time.ex#L1)

Time-scale helpers for astronomical computation.

Julian centuries from J2000.0 is the standard time argument for polynomial
expressions in celestial mechanics (Meeus, IERS, IAU). J2000.0 is the epoch
JD 2451545.0 TT, i.e. 2000 January 1 at 12:00 TT.

This module only rescales a Julian Date; it does not convert between time
scales. Converting UTC to TT (leap seconds plus the 32.184 s TAI offset)
is the caller's responsibility.

# `julian_centuries`

```elixir
@spec julian_centuries(number()) :: float()
```

Convert a Julian Date (TT) to Julian centuries elapsed since J2000.0.

This is the standard `T` argument used in Meeus polynomials, IERS Earth
orientation series, and IAU precession/nutation models. Dates before
J2000.0 give negative values; there is no clamping.

## Examples

    iex> AstroUtils.Time.julian_centuries(2451545.0)
    0.0

    iex> AstroUtils.Time.julian_centuries(2451545.0 + 36525.0)
    1.0

    iex> AstroUtils.Time.julian_centuries(2451545.0 - 36525.0)
    -1.0

---

*Consult [api-reference.md](api-reference.md) for complete listing*