# How to use lookAtMoon() in MoonSpec.js?

**URL:** <https://community.cesium.com/t/how-to-use-lookatmoon-in-moonspec-js/34856>\
**Category:** CesiumJS\
**Created:** [August 30, 2024, 12:59pm UTC](https://community.cesium.com/t/how-to-use-lookatmoon-in-moonspec-js/34856 "2024-08-30T12:59:09Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![jumpjack](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/jumpjack/32/3589_2.png) [@jumpjack](https://community.cesium.com/u/jumpjack)\
**Post date:** [August 30, 2024, 12:59pm UTC](https://community.cesium.com/t/how-to-use-lookatmoon-in-moonspec-js/34856/1 "2024-08-30T12:59:09Z")

</div>

I can’t find any example about [this function](https://github.com/CesiumGS/cesium/blob/2568dfee4b1f213f8adbbc6ba477067ff33d6dbb/packages/engine/Specs/Scene/MoonSpec.js#L29), and apparently Simon1994PlanetaryPositions returns wrong position for Sun and Moon.

My [sandcastle](https://sandcastle.cesium.com/#c=bZDRa8IwEMb/ldCnFlyKsBddlYFMEDYmKHvqS0xPDUvvJLlWuuH/vqTOMdQ8JXe/7/vu0ionWgNHcGIiEI5iBt40tfzoa2mZ6P49I2RlEFyZZE8llnjWSK8BQdZEKP2ejsGDXQO3hFY1OCW3tltT+h3aXIFng4oN4fgSujI14XA0elxahcDKdUvyJiJeaqoPDcNbiLoUF/iiHO8XYSw2ys5dCEmzQXSPtAWGsdg2qCOcZqLPjT30ZEFa2oX9CGd/7Nx2Yk0iZog0zMr0EFfLfpfmU4mneEsGSeG5szAtUfTn2dQHciwaZ1Mpc4ZgqRh8vmn0J7DU3kdhRIv8v7SoTCtMNbnz0UJb5X3obBtrV+YLymRa5IG/kVpSlcHdewvOqi5i++H09VyUUhZ5eN5XMpHdKHfl/AM).

Gray and Yellow: Simon1994 pointing (wrong)  
Red and Orange: [suncalc](https://www.suncalc.org/#/42,12,8/2024.08.30/14:40/1/3) and [mooncalc](https://www.mooncalc.org/#/42,12,8/2024.08.30/14:39/1/3) pointing (right)

Cesium **does** put the Moon and the Sun in the right positions… but WHERE does it store them and how can I access them?  
And how can I access lookAtMoon()? viewer.scene.lookAtMoon() does not work.

---

<div class="post-metadata">

**Author:** ![jumpjack](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/jumpjack/32/3589_2.png) [@jumpjack](https://community.cesium.com/u/jumpjack)\
**Post date:** [August 31, 2024, 2:05pm UTC](https://community.cesium.com/t/how-to-use-lookatmoon-in-moonspec-js/34856/2 "2024-08-31T14:05:14Z")

</div>

I found that rather than using lookAtMoon, I can just reuse its algorithm (but I am still curious about how to access any function which I can find in the source code):

```auto
var specificTime = Cesium.JulianDate.fromDate(new Date(Date.UTC(2024, 7, 31, 4, 0, 0))); // Define custom time
viewer.clock.currentTime = specificTime; // apply to view
const icrfToFixed = new Cesium.Matrix3(); // Setup Matrix to convert from ICRF reference to Fixed reference
Cesium.Transforms.computeTemeToPseudoFixedMatrix(specificTime, icrfToFixed); /// Use time to setup the conversion matrix
var moonPos = Cesium.Simon1994PlanetaryPositions.computeMoonPositionInEarthInertialFrame(specificTime); // Use time to calculate Moon position in ICRF reference
Cesium.Matrix3.multiplyByVector(icrfToFixed, moonPos, moonPos); //Convert moon position from ICRF to Fixed reference

```

Alternative syntax:

```auto
var specificTime = Cesium.JulianDate.fromDate(new Date(Date.UTC(2024, 7, 31, 4, 0, 0))); // Define custom time
viewer.clock.currentTime = specificTime; // apply to view
var icrfToFixed = new Cesium.Transforms.computeTemeToPseudoFixedMatrix(specificTime); /// Use time to make the conversion
var moonPos = Cesium.Simon1994PlanetaryPositions.computeMoonPositionInEarthInertialFrame(specificTime); // Use time to calculate Moon position in ICRF reference
var fixedPos = new Cesium.Matrix3.multiplyByVector(icrfToFixed, moonPos,new Cesium.Cartesian3()); //Convert moon position from ICRF to Fixed reference

```

Sandcastle: [link](https://sandcastle.cesium.com/#c=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)