Light pollution, moonlight and honest expectations

What light pollution does

Stray light scattered into the sky hides the faint stars and leaves only the bright ones.

NASA explains (opens in a new tab) light pollution as stray light from car parks, sports grounds, streetlights and other human activity, scattered into the sky as a glow; the bigger the town, the more of it. There are many more faint stars than bright ones, and in bright urban skies only the brightest stars and planets show.

From a perfectly dark site a person with excellent eyesight may see a few thousand stars (opens in a new tab) at once; most people never have that, because light pollution drastically limits what can be seen across much of the world.

Sources for this section Preston Dyches, How to Find Good Places to Stargaze, NASA Science (2021) (opens in a new tab) · ; Kat Troche (Astronomical Society of the Pacific), Check Your Sky Quality with Orion!, NASA Night Sky Network (2023) (opens in a new tab)

The Moon is light pollution too

For about a week either side of full, moonlight washes out faint stars and the Milky Way.

When the Moon is near full, for the week or so before and after (opens in a new tab), it makes a lot of skyglow, with much the same effect as city light: faint stars and faint objects are harder to see. The darkest evenings are those around new moon, when the Moon is absent or sets early.

For the Milky Way, the Night Sky Network (opens in a new tab) recommends a new or crescent Moon; a full Moon washes it out. Tonight on Cool Moon Facts shows the Moon's phase.

Sources for this section Preston Dyches, How to Find Good Places to Stargaze, NASA Science (2021) (opens in a new tab) · ; Kat Troche (Astronomical Society of the Pacific), The Great Rift, NASA Night Sky Network (2025) (opens in a new tab)

How dark is your sky?

The faintest star you can see overhead is your sky's limiting magnitude.

Your sky's limiting magnitude (opens in a new tab) is the faintest star you can see straight up. If it is about 3, faint stars and meteor showers are a wasted effort; at about 5 you should see meteors and the Milky Way. The Night Sky Network's printable Dark Sky Wheel, with Orion on one side and Scorpius on the other, lets you measure it by eye.

Astronomers also use the Bortle scale (opens in a new tab), from class 1, the darkest skies on Earth, to class 9, the brightest city skies. NASA suggests that for most people a class 3 or 4 site is dark enough for a great evening, and that 20 to 30 miles from the city limits, higher ground, or a ridge between you and the city all help.

Sources for this section Kat Troche (Astronomical Society of the Pacific), Check Your Sky Quality with Orion!, NASA Night Sky Network (2023) (opens in a new tab) · ; Preston Dyches, How to Find Good Places to Stargaze, NASA Science (2021) (opens in a new tab)

What to expect, honestly

Your eyes, binoculars and a small telescope each show more, but never what a long-exposure photograph shows.

By eye from a dark site you can see the Orion Nebula (opens in a new tab) as a soft patch and the Andromeda Galaxy (opens in a new tab) as a fuzzy smudge; even from moderately light-polluted places a persistent observer can catch Andromeda's core.

Binoculars turn the Pleiades and Hyades into fields of stars (opens in a new tab) and show the galaxy M81 (opens in a new tab) as a faint patch; a moderately sized telescope is needed to see the Ring Nebula (opens in a new tab) as a ring.

Photographs show far more detail and colour than the eye can (opens in a new tab). A grey smudge seen with your own eyes is a real sighting of light that has travelled for thousands, or millions, of years.

Sources for this section Kat Troche (Astronomical Society of the Pacific), A Flame in the Sky – the Orion Nebula, NASA Night Sky Network (2023) (opens in a new tab) · ; Kat Troche (Astronomical Society of the Pacific), Catch Andromeda Rising!, NASA Night Sky Network (2024) (opens in a new tab) · ; Kat Troche (Astronomical Society of the Pacific), Spot the Young Stars of the Hyades and Pleiades, NASA Night Sky Network (2023) (opens in a new tab) · ; NASA Hubble, Messier 81 (opens in a new tab) · ; NASA Hubble, Messier 57 (the Ring Nebula) (opens in a new tab) · ; Kat Troche (Astronomical Society of the Pacific), The Great Rift, NASA Night Sky Network (2025) (opens in a new tab)