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Why Can't We See Stars in the Daytime?

Category: Space & Astronomy

At dusk the first star appears, then another, then dozens. It is easy to feel that the stars "come out" at night. But where were they at noon?

They were in the same places. Nothing switched them off. What changes between noon and midnight is the sky behind them, and that is the whole story of this note. We will see how a bright sky hides faint lights, how the sky darkens after sunset, and which objects can still be found in daylight.

1. The Stars Are Still There at Noon; the Sky Is Just Too Bright

Sunlight does not travel to your eyes only in a straight line from the Sun. On the way, it bumps into the molecules of the air and is knocked in every direction. Because you are surrounded by air, light seems to come from every part of the sky, and the whole sky glows[1].

Stars are far fainter than that glow. Scientific American compares looking for a star in the daytime sky to trying to hear a whisper at a heavy metal concert[1]. The whisper has not stopped. It is just buried.

So whether you can see a star depends on contrast: how bright the star is compared with the sky right behind it. At night the sky behind it is dark, so even a faint star stands out. At noon the sky behind it is bright, so the same star disappears.

2. After Sunset the Sky Darkens in Stages, and Fainter Stars Appear

The Sun does not turn off the moment it touches the horizon. The sky stays bright for a while, because the Sun is still lighting the upper air. Scientists describe this stretch of time, called twilight, by how far the center of the Sun has dropped below the horizon. The US National Weather Service lists three steps[2]:

  • Civil twilight, 6 degrees below the horizon: the brightest stars and planets can be seen, and you can still make out the horizon and objects on the ground.
  • Nautical twilight, 12 degrees: the horizon is still visible, even with no Moon. Sailors can take star readings.
  • Astronomical twilight, 18 degrees: the horizon is no longer clear, and moderately faint stars and planets can be seen with the naked eye, if the sky is free of light pollution.

Put the steps in order and you can watch the rule from section 1 at work: as the sky behind the stars gets darker, fainter and fainter stars rise above it. These degrees are guidelines. Clouds, haze, and city lights all change what you can see[2][3].

3. Venus and the Moon Can Be Found by Day Because They Are Very Bright

If a star is bright enough, it can beat the sky. Apart from the Sun and the Moon, Venus is the brightest object in the sky (not counting human-made satellites), and it can be seen in daylight, especially when it is close to the crescent Moon, which acts as a signpost[1]. The Moon itself is the easiest daytime target of all. Near first quarter it can be seen rising in the east before sunset[1].

Even so, Venus is not easy to spot. It is a tiny point of light, and observers advise focusing your eyes on something far away, such as the horizon, before searching, so that your eyes are relaxed for distance[3]. The RASC Calgary Centre, a group of amateur astronomers, lists Venus at about magnitude −4.6 and the Moon at −12.74. In this system a smaller number means a brighter object[3].

4. Ordinary Stars Need a Telescope or Careful Camera Work by Day

Stars are much dimmer than Venus. Amateur observers say the faintest star you could expect to see by day with a telescope is probably brighter than magnitude 4. In their own test on one clear morning, they found stars down to about magnitude 3.3 to 3.5[3]. That is far brighter than the stars visible on a dark night, where stars of about magnitude 6 can be seen[2][3]. (The 6 is a rule of thumb we are adding for comparison; the sources above do not state it directly.)

Scientists have measured daytime stars too. In tests of the Huntsman Telescope Pathfinder in 2024, a camera lens and digital camera measured 35 stars with the Sun up to 30 degrees above the horizon, and detected stars as faint as magnitude 4.6. It took very short exposures and thousands of images[1].

The amateur advice has a clever trick: use a polarizing filter and rotate it. Blue sky light is partly polarized, so the filter can darken the sky while the stars stay about the same. The same page suggests looking at objects about 90 degrees away from the Sun, where this works best[3]. In other words, the trick is not to make the star brighter. It is to make the sky behind it darker, which is the same idea as twilight.

5. Watch the Stars Arrive After Sunset, Safely

On a clear evening, go outside with an adult after the Sun has set. Every ten minutes, count the stars you can see and write down the number, plus a few words about the color of the sky. Does the count grow slowly at first and then faster? If you can, try again from a place with fewer streetlights and compare.

Never look at the Sun, and never point binoculars or a telescope anywhere near it. That includes looking for Venus: if you want to try, use only your eyes, and keep the Sun hidden behind a building or hill. Stay with an adult on dark paths.

If this made you curious, the sources below are the place to go next. The amateur observers' page on daytime stars has tables, tips, and a list of how bright different objects are.

Sources

This article is a personal summary based on the public sources listed below. Each page was fetched through a summarizing tool and not read word for word. We did not find a single source that gives the daytime sky's brightness in numbers, so we do not give one.

  1. Scientific American, "How to See Stars, Satellites, and More in the Daytime Sky." https://www.scientificamerican.com/article/how-to-see-stars-satellites-and-more-in-the-daytime-sky (Supplies the scattering explanation, the whisper comparison, Venus and the Moon by day, and the 2024 Huntsman Telescope Pathfinder figures. Read through a summarizing tool. It mentions no safety rules, so the safety advice is ours.)
  2. US National Weather Service, "Twilight Types." https://www.weather.gov/lmk/twilight-types (Supplies the 6, 12, and 18 degree definitions and what can be seen in each. It gives no star magnitudes, so the magnitude 6 figure in section 4 is a general rule of thumb of ours.)
  3. Royal Astronomical Society of Canada, Calgary Centre, "Seeing Stars in the Daytime." https://calgary.rasc.ca/daystars/index.htm (An amateur astronomers' guide. Supplies the magnitude table, the limit of about magnitude 4, their test result, focusing advice, and the polarizing filter. Read through a summarizing tool. It does not cover safety around the Sun.)

Revision History

  • First published.

Once an article is published, its text is rarely rewritten. If a mistake is found or the information goes out of date, it is corrected and the reason is recorded here.