Module pymap3d.sidereal
manipulations of sidereal time
Source code
# Copyright (c) 2014-2018 Michael Hirsch, Ph.D.
""" manipulations of sidereal time """
from math import pi
from datetime import datetime
from .timeconv import str2dt
try:
from astropy.time import Time
import astropy.units as u
from astropy.coordinates import Longitude
except ImportError:
Time = None
"""
The "usevallado" datetime to julian runs 4 times faster than astropy.
However, AstroPy is more accurate.
"""
__all__ = ["datetime2sidereal", "juliandate", "julian2sidereal"]
def datetime2sidereal(time: datetime, lon_radians: float, usevallado: bool = True) -> float:
"""
Convert ``datetime`` to sidereal time
from D. Vallado "Fundamentals of Astrodynamics and Applications"
time : datetime.datetime
time to convert
lon_radians : float
longitude (radians)
usevallado : bool, optional
use vallado instead of AstroPy (default is Vallado)
Results
-------
tsr : float
Sidereal time
"""
if isinstance(time, (tuple, list)):
return [datetime2sidereal(t, lon_radians) for t in time]
usevallado = usevallado or Time is None
if usevallado:
jd = juliandate(str2dt(time))
# %% Greenwich Sidereal time RADIANS
gst = julian2sidereal(jd)
# %% Algorithm 15 p. 188 rotate GST to LOCAL SIDEREAL TIME
tsr = gst + lon_radians
else:
tsr = Time(time).sidereal_time(kind="apparent", longitude=Longitude(lon_radians, unit=u.radian)).radian
return tsr
def juliandate(time: datetime) -> float:
"""
Python datetime to Julian time
from D.Vallado Fundamentals of Astrodynamics and Applications p.187
and J. Meeus Astronomical Algorithms 1991 Eqn. 7.1 pg. 61
Parameters
----------
time : datetime.datetime
time to convert
Results
-------
jd : float
Julian date
"""
if isinstance(time, (tuple, list)):
return list(map(juliandate, time))
if time.month < 3:
year = time.year - 1
month = time.month + 12
else:
year = time.year
month = time.month
A = int(year / 100.0)
B = 2 - A + int(A / 4.0)
C = ((time.second / 60.0 + time.minute) / 60.0 + time.hour) / 24.0
return int(365.25 * (year + 4716)) + int(30.6001 * (month + 1)) + time.day + B - 1524.5 + C
def julian2sidereal(Jdate: float) -> float:
"""
Convert Julian time to sidereal time
D. Vallado Ed. 4
Parameters
----------
Jdate: float
Julian centuries from J2000.0
Results
-------
tsr : float
Sidereal time
"""
if isinstance(Jdate, (tuple, list)):
return list(map(julian2sidereal, Jdate))
# %% Vallado Eq. 3-42 p. 184, Seidelmann 3.311-1
tUT1 = (Jdate - 2451545.0) / 36525.0
# Eqn. 3-47 p. 188
gmst_sec = 67310.54841 + (876600 * 3600 + 8640184.812866) * tUT1 + 0.093104 * tUT1 ** 2 - 6.2e-6 * tUT1 ** 3
# 1/86400 and %(2*pi) implied by units of radians
return gmst_sec * (2 * pi) / 86400.0 % (2 * pi)Functions
def datetime2sidereal(time, lon_radians, usevallado=True)-
Convert
datetimeto sidereal timefrom D. Vallado "Fundamentals of Astrodynamics and Applications"
time : datetime.datetime time to convert lon_radians : float longitude (radians) usevallado : bool, optional use vallado instead of AstroPy (default is Vallado)
Results
tsr:float- Sidereal time
Source code
def datetime2sidereal(time: datetime, lon_radians: float, usevallado: bool = True) -> float: """ Convert ``datetime`` to sidereal time from D. Vallado "Fundamentals of Astrodynamics and Applications" time : datetime.datetime time to convert lon_radians : float longitude (radians) usevallado : bool, optional use vallado instead of AstroPy (default is Vallado) Results ------- tsr : float Sidereal time """ if isinstance(time, (tuple, list)): return [datetime2sidereal(t, lon_radians) for t in time] usevallado = usevallado or Time is None if usevallado: jd = juliandate(str2dt(time)) # %% Greenwich Sidereal time RADIANS gst = julian2sidereal(jd) # %% Algorithm 15 p. 188 rotate GST to LOCAL SIDEREAL TIME tsr = gst + lon_radians else: tsr = Time(time).sidereal_time(kind="apparent", longitude=Longitude(lon_radians, unit=u.radian)).radian return tsr def julian2sidereal(Jdate)-
Convert Julian time to sidereal time
D. Vallado Ed. 4
Parameters
Jdate:float- Julian centuries from J2000.0
Results
tsr:float- Sidereal time
Source code
def julian2sidereal(Jdate: float) -> float: """ Convert Julian time to sidereal time D. Vallado Ed. 4 Parameters ---------- Jdate: float Julian centuries from J2000.0 Results ------- tsr : float Sidereal time """ if isinstance(Jdate, (tuple, list)): return list(map(julian2sidereal, Jdate)) # %% Vallado Eq. 3-42 p. 184, Seidelmann 3.311-1 tUT1 = (Jdate - 2451545.0) / 36525.0 # Eqn. 3-47 p. 188 gmst_sec = 67310.54841 + (876600 * 3600 + 8640184.812866) * tUT1 + 0.093104 * tUT1 ** 2 - 6.2e-6 * tUT1 ** 3 # 1/86400 and %(2*pi) implied by units of radians return gmst_sec * (2 * pi) / 86400.0 % (2 * pi) def juliandate(time)-
Python datetime to Julian time
from D.Vallado Fundamentals of Astrodynamics and Applications p.187 and J. Meeus Astronomical Algorithms 1991 Eqn. 7.1 pg. 61
Parameters
time:datetime.datetime- time to convert
Results
jd:float- Julian date
Source code
def juliandate(time: datetime) -> float: """ Python datetime to Julian time from D.Vallado Fundamentals of Astrodynamics and Applications p.187 and J. Meeus Astronomical Algorithms 1991 Eqn. 7.1 pg. 61 Parameters ---------- time : datetime.datetime time to convert Results ------- jd : float Julian date """ if isinstance(time, (tuple, list)): return list(map(juliandate, time)) if time.month < 3: year = time.year - 1 month = time.month + 12 else: year = time.year month = time.month A = int(year / 100.0) B = 2 - A + int(A / 4.0) C = ((time.second / 60.0 + time.minute) / 60.0 + time.hour) / 24.0 return int(365.25 * (year + 4716)) + int(30.6001 * (month + 1)) + time.day + B - 1524.5 + C