Calculating your "birth position"

birthpos.jl

using Dates, TimeZones, SatelliteToolbox

"""
    upcoming_birthpos gives you the exact time and date within the
    next year, at which the earth arrives again closest to where it
    was when you were born (relative to the sun). It also gives
    this minimum distance value in km.
"""
function upcoming_birthpos(y,m,d,h,min,s,tzstr="Asia/Kolkata")
    dob = ZonedDateTime(y,m,d,h,min,s,0,TimeZone(tzstr))
    jdthen = datetime2julian(dob.utc_datetime)
    jdnow = datetime2julian(now(tz"UTC").utc_datetime)
    pthen = sun_position_i(jdthen)
        # This is position in earth-centered inertial MOD frame.
        # This means we can use it as relative position of earth
        # from sun as well. To check that this is true, if you
        # calculate the corresponding sun_velocity_i(jdthen),
        # you'll find it correlates well with the earth's orbital
        # speed.
    onemin = 1/(24*60)
    start = 1.0
    trange = (jdnow-start):onemin:(jdnow-start+365)
    dist(p1,p2) = sqrt(sum((p1-p2).^2))
    exact_ix = argmin(dist(pthen, sun_position_i(t)) for t in trange)
    exact_jd = (jdnow-start) + (exact_ix-1)*onemin
    pnow = sun_position_i(exact_jd)
    (;years = (exact_jd - jdthen) / 365.25,
      birthday = ZonedDateTime(julian2datetime(exact_jd), TimeZone(tzstr), from_utc=true),
      distance_from_birthpos_km = dist(pnow,pthen)/1000)
end