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Added solar time. #156

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Added solar time. #156

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8f5890e
Added solar time.
camiteca Feb 4, 2022
f5ce838
Fixed readme not being in sync with the implementation.
camiteca Aug 11, 2022
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11 changes: 11 additions & 0 deletions README.md
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Expand Up @@ -153,8 +153,19 @@ Returns an object with the following properties:
By default, it will search for moon rise and set during local user's day (frou 0 to 24 hours).
If `inUTC` is set to true, it will instead search the specified date from 0 to 24 UTC hours.

### Solar time

```js
SunCalc.getSolarTime(/*Date*/ date, /*Number*/ latitude, /*Number*/ utcOffset)
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Based on the original source code, it appears this should use longitude.
Second parameter should be utcOffset and third parameter should be Longitude.

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Fixed. I've been trying different ways to achieve the same. Missed the readme. Thanks.

```

Returns the solar time of the given date in the given latitude and UTC offset.

## Changelog

#### 1.9.0 — Jan 22, 2022
- Added solar time.

#### 1.8.0 — Dec 22, 2016

- Improved precision of moonrise/moonset calculations.
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5 changes: 3 additions & 2 deletions package.json
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@@ -1,6 +1,6 @@
{
"name": "suncalc",
"version": "1.8.0",
"version": "1.9.0",
"description": "A tiny JavaScript library for calculating sun/moon positions and phases.",
"homepage": "https://github.com/mourner/suncalc",
"keywords": [
Expand All @@ -12,7 +12,8 @@
"sunset",
"twilight",
"moon",
"illumination"
"illumination",
"solar"
],
"author": "Vladimir Agafonkin",
"repository": {
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18 changes: 18 additions & 0 deletions suncalc.js
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Expand Up @@ -308,6 +308,24 @@ SunCalc.getMoonTimes = function (date, lat, lng, inUTC) {
return result;
};

// calculation for solar time based on https://www.pveducation.org/pvcdrom/properties-of-sunlight/solar-time

SunCalc.getSolarTime = function (date, utcOffset, lng) {
// calculate the day of year
var start = new Date(date.getFullYear(), 0, 0);
var diff = (date - start) + ((start.getTimezoneOffset() - date.getTimezoneOffset()) * 60 * 1000);
var dayOfYear = Math.floor(diff / dayMs);

var b = 360 / 365 * (dayOfYear - 81) * rad;
var equationOfTime = 9.87 * sin(2 * b) - 7.53 * cos(b) - 1.5 * sin(b);
var localSolarTimeMeridian = 15 * utcOffset;
var timeCorrection = equationOfTime + 4 * (lng - localSolarTimeMeridian);
var localSolarTime = date.getHours() + timeCorrection / 60 + date.getMinutes() / 60;

var solarDate = new Date(0, 0);
solarDate.setMinutes(+localSolarTime * 60);
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Is there a better way to handle the date object when it crosses between days? Using 23:58 as a starting time would be a good test.

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@thkruz thkruz Jul 27, 2022 •
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I would recommend switching to a date object as the return.

return new Date(date.getTime() + timeCorrection * 60 * 1000);

That will handle the above issue and allow the user to format the date however they want.

return solarDate;
};

// export as Node module / AMD module / browser variable
if (typeof exports === 'object' && typeof module !== 'undefined') module.exports = SunCalc;
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