Lunar Libration

Geocentric and Topocentric libration

Use the lunar-libration end point to obtain either geocentric or topocentric lunar libration values.

Request format

The lunar-librationend point requires a date, and optionally accepts an observer latitude and longitude:

axios({
	"method": "GET",
	"url": "https://api.radiantdrift.com/lunar-libration/[DATE_TIME]",
	"params": {
		["obs": "[LAT,LNG]"]
	}
})

curl "https://api.radiantdrift.com/lunar-libration/[DATE_TIME][?obs=[LAT,LNG]]

Example 1: without observer location

The following request returns the lunar libration for March 20 2015 at 10:11:57.7 UTC:

GET https://api.radiantdrift.com/lunar-libration/2015-03-20T10:11:57.7Z

The expected response is:

{
  "query": {
    "name": "lunar-libration",
    "date": "2015-03-20T10:11:57.700Z"
  },
  "response": {
    "physicalObservations": {
      "physicalLibration": {
        "lat": 0.03829045,
        "lng": -0.03277045
      },
      "opticalLibration": {
        "lat": -1.22533368,
        "lng": 1.2851531
      },
      "totalLibration": {
        "lat": -1.18704323,
        "lng": 1.25238265
      },
      "selenographicPosition": {
        "lat": 0.26167655,
        "lng": 180.87616357
      },
      "selenographicColongitude": 269.12383643,
      "positionAngle": 335.07160049
    }
  }
}

Example 2: with observer location

If the observer location is given, the end point additionally calculates the total topocentric lunar libration. For example, in Svalbard in March 2015 for the total solar eclipse:

GET https://api.radiantdrift.com/lunar-libration/2015-03-20T10:11:57.7Z?obs=78.222133,15.650467

Expected response:

{
  "query": {
    "name": "lunar-libration",
    "date": "2015-03-20T10:11:57.700Z",
    "observer": {
      "lat": 78.222133,
      "lng": 15.650467
    }
  },
  "response": {
    "physicalObservations": {
      "physicalLibration": {
        "lat": 0.03829045,
        "lng": -0.03277045
      },
      "opticalLibration": {
        "lat": -1.22533368,
        "lng": 1.2851531
      },
      "totalLibration": {
        "lat": -1.18704323,
        "lng": 1.25238265
      },
      "selenographicPosition": {
        "lat": 0.26167655,
        "lng": 180.87616357
      },
      "selenographicColongitude": 269.12383643,
      "positionAngle": 335.07160049
    },
    "topocentricLibration": {
      "libration": {
        "lat": -0.25992041,
        "lng": 0.87406513
      },
      "positionAngle": 335.07397418
    }
  }
}

The topocentric libration is typically required for the purposes of simulating the appearance of the Moon at a given time/place, and for determining the effect of the lunar limb on solar eclipse circumstances.