NASA explains that the Moon is always half illuminated by the Sun; the changing phase is how much of that illuminated half we see from Earth as the Moon moves through its orbit.[2]

New Moon

At New Moon the Moon is near the Sun in our sky, so the illuminated side is largely turned away from Earth. This is the phase most associated with dark nights for the Milky Way, faint galaxies, nebulae and meteor showers.[3]

Crescent Moon

A thin crescent spends part of the night near the western or eastern twilight sky depending on whether it is waxing or waning. Because it is present for only part of the night, a crescent can provide a beautiful target without eliminating every dark observing hour.[4]

First and last quarter

At quarter phase we see half of the Moon's Earth-facing disk illuminated. The terminator, the boundary between lunar day and night, creates strong shadows that emphasize crater walls and mountains, making quarter phases especially rewarding in binoculars and telescopes.[5]

Full Moon

A Full Moon rises near sunset and sets near sunrise. Its light reduces contrast in the Milky Way and many faint objects, but Great Sand Dunes points out the other side: a bright Moon can illuminate the dunes and landscape enough to make moonlight the feature of the visit.[6][7]

There is no permanently dark side

NASA explains that the Moon rotates once during each orbit, keeping nearly the same face toward Earth. The far side still receives sunlight and experiences lunar day and night; it is not permanently dark.[8]

Binoculars and telescopes show different scales

Binoculars comfortably frame the whole Moon and make phase changes obvious. A telescope can reveal smaller crater, mountain and mare detail. Begin at low power, then add magnification when the atmosphere and instrument support it.[9]

Check rise and set time, not only phase

NASA notes that Moon rise and set timing changes systematically with phase. A night can begin moonlit and become dark after moonset, or begin dark and brighten when the Moon rises.[10]

For a Colorado Milky Way trip, use the dark hours. For moonlit snow, dunes or mountains, deliberately use the bright ones.[10]

Lunar eclipses

A lunar eclipse occurs when the Moon enters Earth's shadow. NASA notes that lunar eclipses are visible from the nighttime half of Earth and are safe to view directly with the eyes, binoculars or a telescope.[11]

Photography follows a different exposure

NASA's lunar photography guide recommends exposing for the bright Moon itself, stabilizing the camera or phone and using foreground elements when they improve the composition.[12]

Read the Milky Way planning guide.[12]

Sources

  1. [1]

    Photo: NASA / Bill Dunford, Phases of the Moon — science.nasa.gov/resource/phases-of-the-moon-2

  2. [2]

    NASA Science, Moon Phases — science.nasa.gov/moon/moon-phases

  3. [3]

    NASA Science, Moon Phases — science.nasa.gov/moon/moon-phases

  4. [4]

    NASA Science, Moon Phases — science.nasa.gov/moon/moon-phases

  5. [5]

    NASA Science, Moon Viewing Tips — science.nasa.gov/moon/observe-the-moon-night/overview

  6. [6]

    NASA Science, Moon Phases — science.nasa.gov/moon/moon-phases

  7. [7]

    National Park Service, Great Sand Dunes, Experience the Night — nps.gov/grsa/planyourvisit/experiencethenight.htm

  8. [8]

    NASA Science, Moon Phases — science.nasa.gov/moon/moon-phases

  9. [9]

    NASA Science, Skywatching Tips & Guides — Binoculars: A Great First Telescope — science.nasa.gov/skywatching/tips-guides

  10. [10]

    NASA Science, Moon Phases — science.nasa.gov/moon/moon-phases

  11. [11]

    NASA Science, Eclipses and the Moon — science.nasa.gov/moon/eclipses

  12. [12]

    NASA Science, Lunar Photography Guide — science.nasa.gov/moon/photography-guide