Class: Astronoby::Coordinates::Equatorial

Inherits:
Object
  • Object
show all
Defined in:
lib/astronoby/coordinates/equatorial.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(declination:, right_ascension:, hour_angle: nil, epoch: Epoch::DEFAULT_EPOCH) ⇒ Equatorial

Returns a new instance of Equatorial.



8
9
10
11
12
13
14
15
16
17
18
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 8

def initialize(
  declination:,
  right_ascension:,
  hour_angle: nil,
  epoch: Epoch::DEFAULT_EPOCH
)
  @right_ascension = right_ascension
  @declination = declination
  @hour_angle = hour_angle
  @epoch = epoch
end

Instance Attribute Details

#declination ⇒ Object (readonly)

Returns the value of attribute declination.



6
7
8
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 6

def declination
  @declination
end

#epoch ⇒ Object (readonly)

Returns the value of attribute epoch.



6
7
8
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 6

def epoch
  @epoch
end

#hour_angle ⇒ Object (readonly)

Returns the value of attribute hour_angle.



6
7
8
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 6

def hour_angle
  @hour_angle
end

#right_ascension ⇒ Object (readonly)

Returns the value of attribute right_ascension.



6
7
8
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 6

def right_ascension
  @right_ascension
end

Instance Method Details

#compute_hour_angle(time:, longitude:) ⇒ Object 



20
21
22
23
24
25
26
27
28
29
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 20

def compute_hour_angle(time:, longitude:)
  lst = GreenwichSiderealTime
    .from_utc(time.utc)
    .to_lst(longitude: longitude)

  ha = (lst.time - @right_ascension.hours)
  ha += Constants::HOURS_PER_DAY if ha.negative?

  Angle.from_hours(ha)
end

#to_ecliptic(epoch:) ⇒ Object

Source:

Title: Celestial Calculations
Author: J. L. Lawrence
Edition: MIT Press
Chapter: 4 - Orbits and Coordinate Systems



60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 60

def to_ecliptic(epoch:)
  mean_obliquity = MeanObliquity.for_epoch(epoch)

  y = Angle.from_radians(
    @right_ascension.sin * mean_obliquity.cos +
    @declination.tan * mean_obliquity.sin
  )
  x = Angle.from_radians(@right_ascension.cos)
  r = Angle.atan(y.radians / x.radians)
  longitude = Util::Trigonometry.adjustement_for_arctangent(y, x, r)

  latitude = Angle.asin(
    @declination.sin * mean_obliquity.cos -
    @declination.cos * mean_obliquity.sin * @right_ascension.sin
  )

  Ecliptic.new(
    latitude: latitude,
    longitude: longitude
  )
end

#to_epoch(epoch) ⇒ Object 



82
83
84
85
86
87
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 82

def to_epoch(epoch)
  Precession.for_equatorial_coordinates(
    coordinates: self,
    epoch: epoch
  )
end

#to_horizontal(time:, observer:) ⇒ Object 



31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
 
# File 'lib/astronoby/coordinates/equatorial.rb', line 31

def to_horizontal(time:, observer:)
  latitude = observer.latitude
  longitude = observer.longitude
  ha = @hour_angle || compute_hour_angle(time: time, longitude: longitude)
  t0 = @declination.sin * latitude.sin +
    @declination.cos * latitude.cos * ha.cos
  altitude = Angle.asin(t0)

  t1 = @declination.sin - latitude.sin * altitude.sin
  t2 = t1 / (latitude.cos * altitude.cos)
  azimuth = Angle.acos(t2)

  if ha.sin.positive?
    azimuth =
      Angle.from_degrees(Constants::DEGREES_PER_CIRCLE - azimuth.degrees)
  end

  Horizontal.new(
    azimuth: azimuth,
    altitude: altitude,
    observer: observer
  )
end