Handle geocentric parallax

[rhannequin]

The geocentric parallax is the phenomenon which makes appear close observed bodies at different locations in the sky depending on where the observer is at the surface of the Earth. It takes into account the distance of the body, and the fact that the Earth surface is not a perfect sphere.

This introduces a GeocentricParallax class which can calculate the parallax angle and apply it to true equatorial coordinates into apparent equatorial coordinates.

moon_earth_distance = 358_586_861 # meters

parallax_angle = Astronoby::GeocentricParallax.angle(
  distance: moon_earth_distance
)

parallax_angle.str(:dms)
# => "+1° 1′ 8.9999″"

latitude = Astronoby::Angle.as_degrees(50)
longitude = Astronoby::Angle.as_degrees(-100)
elevation = 60
time = Time.utc(1979, 2, 26, 16, 45)
true_coordinates = Astronoby::Coordinates::Equatorial.new(
  right_ascension: Astronoby::Angle.as_hms(22, 35, 19),
  declination: Astronoby::Angle.as_dms(-7, 41, 13)
)
distance = 358_586_861

apparent_coordinates = described_class.for_equatorial_coordinates(
  latitude: latitude,
  longitude: longitude,
  elevation: elevation,
  time: time,
  coordinates: true_coordinates,
  distance: distance
)

true_coordinates.right_ascension.str(:hms)
# => "22h 35m 19.0s"
apparent_coordinates.right_ascension.str(:hms)
# => "22h 36m 43.2195s"

true_coordinates.declination.str(:dms)
# => "-7° 41′ 13.0″"
apparent_coordinates.declination.str(:dms)
# => "-8° 32′ 17.3947″"