L0#

sunpy.coordinates.sun.L0(
time='now',
light_travel_time_correction=True,
nearest_point=True,
aberration_correction=False,
)[source]#

Return the L0 angle for the Sun at a specified time, which is the apparent Carrington longitude of the Sun-disk center as seen from Earth.

Observer corrections can be disabled, and then this function will instead return the true Carrington longitude.

Parameters:
  • time (tuple, list, str, pandas.Timestamp, pandas.Series, pandas.DatetimeIndex, datetime.datetime, datetime.date, numpy.datetime64, numpy.ndarray, astropy.time.Time) – Time to use in a parse_time-compatible format

  • light_travel_time_correction (bool) – If True, apply the correction for light travel time from Sun to Earth. Defaults to True.

  • nearest_point (bool) – If True, calculate the light travel time to the nearest point on the Sun’s surface rather than the light travel time to the center of the Sun (i.e., a difference of the solar radius). Defaults to True.

  • aberration_correction (bool) – If True, apply the stellar-aberration correction due to Earth’s motion. Defaults to False.

Returns:

Longitude – The Carrington longitude

Notes

This longitude is calculated using current IAU values (Seidelmann et al. [SAAhearn+07] and later), which do not include the effects of light travel time and aberration due to Earth’s motion (see that paper’s Appendix). This function then, by default, applies the light-travel-time correction for the nearest point on the Sun’s surface, but does not apply the stellar-aberration correction due to Earth’s motion.

We do not apply the stellar-aberration correction by default because it should not be applied for purposes such as co-aligning images that are each referenced to Sun-disk center. Stellar aberration does not shift the apparent positions of solar features relative to the Sun-disk center.

The Astronomical Almanac applies the stellar-aberration correction in their printed published L0 values (see also Urban & Kaplan 2007). Applying the stellar-aberration correction due to Earth’s motion decreases the apparent Carrington longitude by ~20.5 arcseconds.

References

  • Urban & Kaplan (2007), “Investigation of Change in the Computational Technique of the Sun’s Physical Ephemeris in The Astronomical Almanac” (link)