astro
Amateur astronomical computations
https://github.com/aligusnet/astro
LTS Haskell 22.36: | 0.4.3.0 |
Stackage Nightly 2024-10-04: | 0.4.3.0 |
Latest on Hackage: | 0.4.3.0 |
astro-0.4.3.0@sha256:b660c6d248b247343b416b6c9dd622b031f8f2703f12fef29e1e51c97abc914c,3698
Module documentation for 0.4.3.0
Amateur astronomical computations
Usage
Install stack
It will take care of everything.
Build the project
stack build
Run unit tests
stack test
Documentation
Useful types
Decimal hours and Decimal degrees
Types to represent hours (used in celestial coordinate systems and as time zone) and degrees (used in coordinate systems).
import Data.Astro.Types
-- 10h 15m 19.7s
dh :: DecimalHours
dh = fromHMS 10 15 19.7
-- DH 10.255472222222222
(h, m, s) = toHMS dh
-- (10,15,19.699999999999562)
-- 51°28′40″
dd :: DecimalDegrees
dd = fromDMS 51 28 40
-- DD 51.477777777777774
(d, m, s) = toDMS dd
-- (51,28,39.999999999987494)
Geographic Coordinates
import Data.Astro.Types
-- the Royal Observatory, Greenwich
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
-- GeoC {geoLatitude = DD 51.4778, geoLongitude = DD (-0.0014)}
Time
The main time datetime type used in the library is JulianDate
defined in Data.Astro.Time.JulianDate
. JulianDate is just a number of days since noon of 1 January 4713 BC:
import Data.Astro.Time.JulianDate
-- 2017-06-25 9:29:00 (GMT)
jd :: JulianDate
jd = fromYMDHMS 2017 6 25 9 29 0
-- JD 2457929.895138889
LocalCiviTime
and LocalCivilDate
are Julian dates with time zones:
import Data.Astro.Time.JulianDate
import Data.Astro.Types
-- 2017-06-25 10:29:00 +0100 (BST)
lct :: LocalCivilTime
lct = lctFromYMDHMS (DH 1) 2017 6 25 10 29 0
-- 2017-06-25 10:29:00.0000 +1.0
lctJD :: JulianDate
lctJD = lctUniversalTime lct
-- JD 2457929.895138889
lctTZ :: DecimalHours
lctTZ = lctTimeZone lct
-- DH 1.0
lcd :: LocalCivilDate
lcd = lcdFromYMD (DH 1) 2017 6 25
lcdJD :: JulianDate
lcdJD = lcdDate lcd
-- JD 2457929.5
lcdTZ :: DecimalHours
lcdTZ = lcdTimeZone lcd
-- DH 1.0
Celestial coordinate systems
The celestical coordinate systems are defined in Data.Astro.Coordinate
.
If you would like to locate Sirius in the sky you need to know the altitude or ‘how far up’ angle in the sky and azimuth - ‘how far round’ angle from the north direction to the east. this describes the Horizontal coordinate system:
import Data.Astro.Coordinate
import Data.Astro.Types
hc :: HorizonCoordinates
hc = HC (DD 30.5) (DD 180)
-- HC {hAltitude = DD 30.0, hAzimuth = DD 180.0}
Unfortunately the Horizontal coordinate system values depend on the position of the observer. And it’s not handy when you need to share coordinates of some celestial object with your friend in Japan.
The second coordinate system is the Equatorial coordinate system. This coordinate system uses the location of the centre of the Earth as the zero point so it does not depend on the observer’s location.
We have two flavours of equatorial coordinates:
-
the first one uses the vernal equinox as a starting direction for the ‘how far round’ coordinate (right ascension, α),
-
the second one uses the meridian instead of the vernal equinox (hour angle).
We can consider the second one as a transition coordinate system between the horizontal one and the ‘true’ equatorial one.
import Data.Astro.Coordinate
import Data.Astro.Types
ec1 :: EquatorialCoordinates1
ec1 = EC1 (DD 71.7) (DH 8)
-- EC1 {e1Declination = DD 71.7, e1RightAscension = DH 8.0}
ec2 :: EquatorialCoordinates2
ec2 = EC1 (DD 77.7) (DH 11)
-- EC2 {e2Declination = DD 77.7, e2HoursAngle = DH 11.0}
Transformations
Say, now is 2017-06-25 10:29 BST and we are somewhere near the Royal Observatory, Greenwich.
Let convert the current location of the Sun in horizon coordinates (altitude: 49°18′21.77″, azimuth: 118°55′19.53″) to equatorial coordinates and back to horizon ones:
import Data.Astro.Time.JulianDate
import Data.Astro.Coordinate
import Data.Astro.Types
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
dt :: LocalCivilTime
dt = lctFromYMDHMS (DH 1) 2017 6 25 10 29 0
sunHC :: HorizonCoordinates
sunHC = HC (fromDMS 49 18 21.77) (fromDMS 118 55 19.53)
-- HC {hAltitude = DD 49.30604722222222, hAzimuth = DD 118.92209166666666}
sunEC2 :: EquatorialCoordinates2
sunEC2 = horizonToEquatorial (geoLatitude ro) sunHC
-- EC2 {e2Declination = DD 23.378295912623855, e2HoursAngle = DH 21.437117068873537}
sunEC1 :: EquatorialCoordinates1
sunEC1 = EC1 (e2Declination sunEC2) (haToRA (e2HoursAngle sunEC2) (geoLongitude ro) (lctUniversalTime dt))
-- EC1 {e1Declination = DD 23.378295912623855, e1RightAscension = DH 6.29383725890224}
sunEC2' :: EquatorialCoordinates2
sunEC2' = EC2 (e1Declination sunEC1) (raToHA (e1RightAscension sunEC1) (geoLongitude ro) (lctUniversalTime dt))
-- EC2 {e2Declination = DD 23.378295912623855, e2HoursAngle = DH 21.437117068873537}
sunHC' :: HorizonCoordinates
sunHC' = equatorialToHorizon (geoLatitude ro) sunEC2'
-- HC {hAltitude = DD 49.30604722222222, hAzimuth = DD 118.92209166666666}
You can use function-shortcuts to simplify transformation EquatorialCoordinates1 <-> HorizonCoordinates: ec1ToHC
and hcToEC1
:
import Data.Astro.Time.JulianDate
import Data.Astro.Coordinate
import Data.Astro.Types
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
dt :: LocalCivilTime
dt = lctFromYMDHMS (DH 1) 2017 6 25 10 29 0
sunHC :: HorizonCoordinates
sunHC = HC (fromDMS 49 18 21.77) (fromDMS 118 55 19.53)
-- HC {hAltitude = DD 49.30604722222222, hAzimuth = DD 118.92209166666666}
sunEC1 :: EquatorialCoordinates1
sunEC1 = hcToEC1 ro (lctUniversalTime dt) sunHC
-- EC1 {e1Declination = DD 23.378295912623855, e1RightAscension = DH 6.29383725890224}
sunHC' :: HorizonCoordinates
sunHC' = ec1ToHC ro (lctUniversalTime dt) sunEC1
-- HC {hAltitude = DD 49.30604722222222, hAzimuth = DD 118.92209166666666}
Stars
The ancient astronomers noted that there were 2 types of stars: some of them were fixed, travelling the same way across the sky every sidereal day and another were wanderers (planetai in ancient Greek).
Of course, stars are not fixed, they are travelling with high speeds but distances to them are so high that their movement is very difficult to note. So we can assume that they are fixed for our purposes.
Given the “fixed” equatorial coordinates of the star we only need to transform them to the horizon coordinates to find out where the star in the sky.
In the example below we will use Data.Astro.Star
module which defines equatorial coordinates of some stars:
import Data.Astro.Time.JulianDate
import Data.Astro.Coordinate
import Data.Astro.Types
import Data.Astro.Star
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
dt :: LocalCivilTime
dt = lctFromYMDHMS (DH 1) 2017 6 25 10 29 0
-- Calculate location of Betelgeuse
betelgeuseEC1 :: EquatorialCoordinates1
betelgeuseEC1 = starCoordinates Betelgeuse
-- EC1 {e1Declination = DD 7.407064, e1RightAscension = DH 5.919529}
betelgeuseHC :: HorizonCoordinates
betelgeuseHC = ec1ToHC ro (lctUniversalTime dt) betelgeuseEC1
-- HC {hAltitude = DD 38.30483892505852, hAzimuth = DD 136.75755644642248}
Rise and Set
Data.Astro.CelestialObject.RiseSet
module defines RiseSet
type to represent time and azimuth of rise and set.
Let calculate rise and set time of Rigel:
import Data.Astro.Time.JulianDate
import Data.Astro.Coordinate
import Data.Astro.Types
import Data.Astro.Effects
import Data.Astro.CelestialObject.RiseSet
import Data.Astro.Star
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
today :: LocalCivilDate
today = lcdFromYMD (DH 1) 2017 6 25
-- Calculate location of Betelgeuse
rigelEC1 :: EquatorialCoordinates1
rigelEC1 = starCoordinates Rigel
verticalShift :: DecimalDegrees
verticalShift = refract (DD 0) 12 1012
-- DD 0.5660098245614035
rigelRiseSet :: RiseSetLCT
rigelRiseSet = riseAndSetLCT ro today verticalShift rigelEC1
-- RiseSet (2017-06-25 06:38:18.4713 +1.0,DD 102.51249855335433) (2017-06-25 17:20:33.4902 +1.0,DD 257.48750144664564)
As we can see Rigel rose today at 06:38:18 and will set at 17:20:33, azimuths of rise and set 102.51° and 257.49° correspondingly.
We used refract
function of Data.Astro.Effects
module with reasonable default parameters to calculate vertical shift.
Planets
The planets is completely different story. We cannot assume that the planets have “fixed” location in equatorial coordinates like stars.
What we can do is to describe details of the planets’ orbit and calculate their positions at any given moment.
Planets and planet details are defined in Data.Astro.Planet
module. j2010PlanetDetails
returns details for the given planet.
This module also defines planetPosition
, planetDistance1
and planetAngularDiameter
to calculate position of the given planet, distance to the planet and angular size of the planet correspondingly.
1
at the end of the planetDistance1
means that this function uses not very precise method to do calculations. Sometimes there are 2
-methods available in the library, but not always.
Let us do some planets-related calculations.
Do some initialisation:
import Data.Astro.Time.JulianDate
import Data.Astro.Coordinate
import Data.Astro.Types
import Data.Astro.Effects
import Data.Astro.CelestialObject.RiseSet
import Data.Astro.Planet
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
dt :: LocalCivilTime
dt = lctFromYMDHMS (DH 1) 2017 6 25 10 29 0
today :: LocalCivilDate
today = lcdFromYMD (DH 1) 2017 6 25
jupiterDetails :: PlanetDetails
jupiterDetails = j2010PlanetDetails Jupiter
earthDetails :: PlanetDetails
earthDetails = j2010PlanetDetails Earth
jupiterPosition :: JulianDate -> EquatorialCoordinates1
jupiterPosition = planetPosition planetTrueAnomaly1 jupiterDetails earthDetails
Calculate Jupiter’s coordinates:
jupiterEC1 :: EquatorialCoordinates1
jupiterEC1 = jupiterPosition (lctUniversalTime dt)
-- EC1 {e1Declination = DD (-4.104626810672402), e1RightAscension = DH 12.863365504382228}
jupiterHC :: HorizonCoordinates
jupiterHC = ec1ToHC ro (lctUniversalTime dt) jupiterEC1
-- HC {hAltitude = DD (-30.67914598469227), hAzimuth = DD 52.29376845044007}
As be can see Jupiter is below the horizon now (the altitude is negative), that’s unfortunate.
Now let us calculate distance to Jupiter:
jupiterDistance :: AstronomicalUnits
jupiterDistance = planetDistance1 jupiterDetails earthDetails (lctUniversalTime dt)
-- AU 5.193435872521039
1 Astronomical Unit is an average distance from the Earth to the Sun.
and calculate an angular size now:
jupiterAngularSize :: DecimalDegrees
jupiterAngularSize = planetAngularDiameter jupiterDetails jupiterDistance
-- DD 1.052289877865987e-2
toDMS jupiterAngularSize
-- (0,0,37.88243560317554)
Rise and Set
Calculate rise and set times of planets are not easy task, because planets change their equatorial coordinates during the day.
riseAndSet2
function of Data.Astro.CelestialObject.RiseSet
module applies iterative approach: calculates rise and set date for midday coordinates and then recalculates rise time for rise coordinates and set for set coordinates obtained from the previous step:
verticalShift :: DecimalDegrees
verticalShift = refract (DD 0) 12 1012
-- DD 0.5660098245614035
jupiterRiseSet :: RiseSetMB
jupiterRiseSet = riseAndSet2 0.000001 jupiterPosition ro verticalShift today
-- RiseSet
-- (Just (2017-06-25 13:53:27.3109 +1.0,DD 95.88943953535569))
-- (Just (2017-06-25 01:21:23.5835 +1.0,DD 264.1289033612776))
We can see now why at 10 am Jupiter is below horizon because it will rise only at 1:53 pm.
Sun
Some examples of doing the Sun’s related calculations:
import Data.Astro.Time.JulianDate
import Data.Astro.Coordinate
import Data.Astro.Types
import Data.Astro.Sun
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
dt :: LocalCivilTime
dt = lctFromYMDHMS (DH 1) 2017 6 25 10 29 0
today :: LocalCivilDate
today = lcdFromYMD (DH 1) 2017 6 25
jd :: JulianDate
jd = lctUniversalTime dt
verticalShift :: DecimalDegrees
verticalShift = refract (DD 0) 12 1012
-- distance from the Earth to the Sun in kilometres
distance :: Double
distance = sunDistance jd
-- 1.5206375976421073e8
-- Angular Size
angularSize :: DecimalDegrees
angularSize = sunAngularSize jd
-- DD 0.5244849215333616
-- The Sun's coordinates
ec1 :: EquatorialCoordinates1
ec1 = sunPosition2 jd
-- EC1 {e1Declination = DD 23.37339098989099, e1RightAscension = DH 6.29262026252748}
hc :: HorizonCoordinates
hc = ec1ToHC ro jd ec1
-- HC {hAltitude = DD 49.312050979507404, hAzimuth = DD 118.94723825710143}
-- Rise and Set
riseSet :: RiseSetMB
riseSet = sunRiseAndSet ro 0.833333 today
-- RiseSet
-- (Just (2017-06-25 04:44:04.3304 +1.0,DD 49.043237261724215))
-- (Just (2017-06-25 21:21:14.4565 +1.0,DD 310.91655607595595))
Moon
The Moon’s related calculations. Data.Astro.Moon
module defines 2 new types of functions we haven’t seen before: moonPhase
and moonBrightLimbPositionAngle
which calculate the phase (the area of the visible segment expressed as a fraction of the whole disk) and the position-angle which is the angle of the midpoint of the illuminated limb measured eastwards from the north point of the disk.
import Data.Astro.Time.JulianDate
import Data.Astro.Coordinate
import Data.Astro.Types
import Data.Astro.Effects
import Data.Astro.CelestialObject.RiseSet
import Data.Astro.Moon
ro :: GeographicCoordinates
ro = GeoC (fromDMS 51 28 40) (-(fromDMS 0 0 5))
dt :: LocalCivilTime
dt = lctFromYMDHMS (DH 1) 2017 6 25 10 29 0
today :: LocalCivilDate
today = lcdFromYMD (DH 1) 2017 6 25
jd :: JulianDate
jd = lctUniversalTime dt
-- distance from the Earth to the Moon in kilometres
mdu :: MoonDistanceUnits
mdu = moonDistance1 j2010MoonDetails jd
-- MDU 0.9550170577020396
distance :: Double
distance = mduToKm mdu
-- 367109.51199772174
-- Angular Size
angularSize :: DecimalDegrees
angularSize = moonAngularSize mdu
-- DD 0.5425033990980761
-- The Moon's coordinates
position :: JulianDate -> EquatorialCoordinates1
position = moonPosition1 j2010MoonDetails
ec1 :: EquatorialCoordinates1
ec1 = position jd
-- EC1 {e1Declination = DD 18.706180658927323, e1RightAscension = DH 7.56710547682055}
hc :: HorizonCoordinates
hc = ec1ToHC ro jd ec1
-- HC {hAltitude = DD 34.57694951316064, hAzimuth = DD 103.91119101451832}
-- Rise and Set
riseSet :: RiseSetMB
riseSet = riseAndSet2 0.000001 position ro verticalShift today
-- RiseSet
-- (Just (2017-06-25 06:22:51.4858 +1.0,DD 57.81458864497365))
-- (Just (2017-06-25 22:28:20.3023 +1.0,DD 300.4168238905249))
-- Phase
phase :: Double
phase = moonPhase j2010MoonDetails jd
-- 2.4716141948212922e-2
sunEC1 :: EquatorialCoordinates1
sunEC1 = sunPosition2 jd
-- EC1 {e1Declination = DD 23.37339098989099, e1RightAscension = DH 6.29262026252748}
limbAngle :: DecimalDegrees
limbAngle = moonBrightLimbPositionAngle ec1 sunEC1
-- DD 287.9869373767473