New Moon Explained: Why the Moon Disappears

New moon opens every lunar month. With the unlit side facing Earth, the Moon is usually invisible to the naked eye; it is an important reference point for calendar calculations.

What happens at new moon?

The Moon steps between the Sun and Earth, almost on one line. The Sun lights the far half of the lunar globe while the near half stays in shadow. From Earth the disc is invisible: illumination 0–1%, moon age ~0 days.

The exact astronomical instant is the conjunction of the Moon and the Sun in ecliptic longitude. In everyday life and in calendars, the whole calendar day counts as the new moon day.

Where is the Moon at new moon?

It travels across the sky together with the Sun:

So for most new moons the Moon is not visible at night: it is below the horizon, or above it but lost in the Sun's glare. By day the unlit disc is not visible either — it disappears in sunlight.

One caveat: in some months the conjunction happens well away from the ecliptic and the Moon stays a noticeable angle from the Sun. The evening sky is then not left empty.

Why is a new moon treated as dark-sky time?

Without moonlight the sky is usually noticeably darker than at other phases. How dark depends on other factors too — city light pollution, atmospheric transparency and how far the Sun sits below the horizon at twilight. For most observers that means:

• the best time for the Milky Way, galaxies and meteor showers;
• the reference point for astronomers and astrophotographers;
• the reason "dark sky" in calendars is marked around new moon.

To see the stars, plan a trip out of the city within ±3 days of new moon.

New moon and solar eclipses

A solar eclipse is possible only at new moon — and only when new moon occurs near a lunar node, where the Moon's orbit crosses the ecliptic plane. Because the lunar orbit is tilted by ~5°, the alignment happens not every month but 2–5 times a year. The total or annular phase is visible along a narrow path, while a partial eclipse covers a wider area.

Waxing crescent: the first sign of the new cycle

One or two days after new moon a thin waxing crescent ("neomenia") appears near the western horizon in the evening. In antiquity priests watched for it — this is how a new month began in lunar calendars. The crescent thickens every evening — the cycle is on its way to first quarter.

How to follow new moons on lunar.day

The moon/phase/[date] page for your city shows the selected date in the local time zone. On the new-moon day illumination is at its minimum and the lunar-day cycle begins again.

Summing up

New moon is the start of the cycle: ~0% illumination, an unobservable disc, the Moon walking the sky near the Sun. It begins the astronomical age count, offers the best observing on a clear moonless night, and opens the only window for solar eclipses.