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Moon Phase Calculator

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Properti	Nilai
Phase
Illumination
Moon Age
Synodic Cycle
Next New Moon
Next Full Moon
Zodiac Constellation

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Moon Phase Calculator

The Moon Phase Calculator shows you exactly what the Moon looks like on any date from 1900 to 2100. Pick a day and instantly see an accurate moon disc, the phase name, illumination percentage, the Moon’s age in the current lunar cycle, and how many days remain until the next new and full Moons. A monthly calendar view reveals the whole lunation at a glance, and a Southern Hemisphere toggle flips the disc so the orientation matches what you see from your sky.

Cara Penggunaan

Open the calculator and pick any date in the date field. It defaults to today so you can see the current Moon at first glance.
Switch the Hemisphere selector to Southern if you are viewing from south of the equator. The moon disc flips horizontally so it matches your sky.
Read the phase name, illumination percentage, Moon age, next new Moon, next full Moon, and the zodiac constellation in the details panel.
Tick Show Monthly Calendar to render every day of the chosen month as its own miniature moon disc, with new, first quarter, full, and last quarter days labelled.
Gunakan Copy Details button to grab the report as plain text, or Unduh SVG to save the moon disc as a vector file you can drop into any design.

Fitur

Accurate phase math – Uses the synodic month and Julian Date to compute the lunar age and illumination from a known reference new Moon.
Visual moon disc – Renders the lit portion as a clean SVG path so the shape is precise at any size, with a subtle texture and glow for atmosphere.
Monthly calendar grid – Shows every day of the chosen month with its own mini moon, plus tags for major phase milestones.
Northern and Southern hemisphere – Mirrors the disc horizontally for viewers in the southern hemisphere, where the terminator faces the opposite way.
Zodiac constellation – Approximates the Moon’s ecliptic longitude so you can see which sign the Moon sits in on your chosen date.
Salin & unduh – Export the full phase report as text or save the moon disc as a scalable SVG.
Runs locally in your browser – No tracking, no API calls, no data leaves your device.

 Tanya Jawab Umum

What is a synodic month?

A synodic month is the average time it takes the Moon to return to the same phase as seen from Earth, about 29.530588 days. It is longer than the sidereal month (27.32 days) because the Earth-Moon system is also moving around the Sun, so the Moon has to travel slightly further to line up with the Sun again. The synodic period is the basis of every lunar phase calculation.
What does illumination percentage actually measure?

Illumination is the fraction of the Moon's Earth-facing disc that is currently lit by the Sun. It runs from 0% at new Moon to 100% at full Moon, following the formula (1 - cos(phase angle)) / 2. Because the relationship is sinusoidal rather than linear, the visible disc fills and empties faster around the quarters than it does near new or full Moon.
Why does the Moon look flipped in the Southern Hemisphere?

Observers in the Northern and Southern Hemispheres look at the Moon from opposite sides of the Earth, so the disc appears rotated by 180 degrees relative to each other. A waxing crescent that is lit on the right in the Northern Hemisphere is lit on the left for viewers near Sydney or Cape Town. Practically, you can think of it as the same moon viewed upside-down.
What is the difference between waxing and waning?

Waxing means the lit portion is growing, between new Moon and full Moon. Waning means the lit portion is shrinking, between full Moon and the next new Moon. Crescent describes any phase where less than half the disc is lit, while gibbous describes a phase where more than half is lit. Combining the two words gives the four intermediate phases: waxing crescent, waxing gibbous, waning gibbous, and waning crescent.
How accurate is a simple synodic-month phase calculation?

A linear synodic-month model is accurate to within a few hours over a span of a century or two, which is fine for everyday use, calendars, photography planning, and storytelling. Professional ephemerides instead use perturbation theory that accounts for the Moon's elliptical orbit, the Sun's gravity, and other forces to deliver sub-second precision. For visual phase prediction the simpler model is almost always good enough.