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I had to require('./astronomy.js') instead of require('astronomy.js')
to get the nodejs demos working, now that I maintain a redundant
copy of astronomy.js in the demo directories.
78 lines
2.5 KiB
JavaScript
78 lines
2.5 KiB
JavaScript
/*
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moonphase.js - by Don Cross - 2019-05-13
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Example Node.js program for Astronomy Engine:
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https://github.com/cosinekitty/astronomy
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This program calculates the Moon's phase for a given date and time,
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or for the computer's current date and time if none is given.
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It also finds the dates and times of the subsequent 10 quarter phase changes.
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To execute, run the command:
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node moonphase [date]
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*/
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const Astronomy = require('./astronomy.js');
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function Pad(s, w) {
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s = s.toFixed(0);
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while (s.length < w) {
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s = '0' + s;
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}
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return s;
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}
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function FormatDate(date) {
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var year = Pad(date.getUTCFullYear(), 4);
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var month = Pad(1 + date.getUTCMonth(), 2);
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var day = Pad(date.getUTCDate(), 2);
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var hour = Pad(date.getUTCHours(), 2);
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var minute = Pad(date.getUTCMinutes(), 2);
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var svalue = date.getUTCSeconds() + (date.getUTCMilliseconds() / 1000);
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var second = Pad(Math.round(svalue), 2);
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return `${year}-${month}-${day} ${hour}:${minute}:${second} UTC`;
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}
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function ParseDate(text) {
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const d = new Date(text);
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if (!Number.isFinite(d.getTime())) {
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console.error(`ERROR: Not a valid date: "${text}"`);
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process.exit(1);
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}
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return d;
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}
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function Demo() {
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const date = (process.argv.length === 3) ? ParseDate(process.argv[2]) : new Date();
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// Calculate the Moon's current phase angle,
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// which ranges from 0 to 360 degrees.
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// 0 degrees = new moon,
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// 90 degrees = first quarter,
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// 180 degrees = full moon,
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// 270 degrees = third quarter.
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const phase = Astronomy.MoonPhase(date);
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console.log(`${FormatDate(date)} : Moon's phase angle = ${phase.toFixed(6)} degrees.`);
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console.log('');
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// Now we predict when the next 10 lunar quarter phases will happen.
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console.log('The next 10 lunar quarters are:');
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const QuarterName = ['New Moon', 'First Quarter', 'Full Moon', 'Third Quarter'];
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let mq;
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for (let i=0; i < 10; ++i) {
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if (mq === undefined) {
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// The first time around the for loop, we search forward
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// from the current date and time to find the next quarter
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// phase, whatever it might be.
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mq = Astronomy.SearchMoonQuarter(date);
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} else {
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// Use the previous moon quarter information to find the next quarter phase event.
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mq = Astronomy.NextMoonQuarter(mq);
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}
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console.log(`${FormatDate(mq.time.date)} : ${QuarterName[mq.quarter]}`);
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}
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}
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Demo();
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process.exit(0);
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