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How many stars can you see on a moonless night?

How many stars can you see?

Imagine you’re far away from city lights, under a dark sky, on a night with no moon, no clouds and no haze. How many stars could you see with your unaided eye? There’s really no definitive answer to this question. No one has counted all the stars in the night sky, and astronomers use different numbers as theoretical estimates.

Considering all the stars visible in all directions around Earth, the upper end on the estimates is close to 10,000 visible stars. Here’s how one source, astronomytrek.com, comes up with that number:

The brighter the star, the lower the apparent magnitude value assigned to it, with the most luminous given a negative number. In total there are 22 stars with magnitudes of between -1 and 1, making them the night sky’s brightest stars. In the meantime, there are 71 stars of 2nd magnitude, 190 stars of 3rd magnitude, 610 of 4th magnitude, 1,929 of 5th magnitude, and 5,946 of 6th magnitude. When we include another 3,150 stars at the limit of our visual acuity of magnitude +6.5, then this adds up to 9,096 stars that it is possible to see in the night sky from both the Northern and Southern Hemispheres with the unaided eye.

Of course, in the Northern Hemisphere, for example, you can’t see stars below the southern horizon in the Southern Hemisphere. So, therefore, each hemisphere can only see about 5,000 stars. And, at any given time, half of Earth is in daylight. So only half the estimated number – perhaps 2,500 stars – would be visible from Earth’s night side. Plus, another fraction of those visible stars would be lost in the murk surrounding your horizon. That could bring you down to around 2,000, the most common number you’ll see for these estimates.

Black and white image of the Milky Way reflected in a large body of water with dark hills behind.
View at EarthSky Community Photos. | How many stars can you see? Well, twice as many if you count their reflections in the water. Chuck Reinhart in Vincennes, Indiana, captured this image on August 6, 2023. Chuck wrote: “This is a composite of 4 photos taken at different times and places to show the Milky Way on the Wabash River.” Thank you, Chuck!

Factors that affect your seeing

Why can’t astronomers agree on the number of visible stars? It’s because we don’t all see the sky in the same way. Even under ideal conditions, there’s a fair amount of variation between how well people can see the stars. Some of the factors include the strength of your vision and your age. As you get older, for example, your eyes become much less sensitive to faint light. Remember, too, that it takes up to 30 minutes for your eyes to adapt to the darkness.

You also have to take into account the brightness of your night sky. Even on a moonless night, the glow of lights from Earth’s surface brightens the sky.

Still, far from city lights – under absolutely perfect conditions of darkness and sky clarity – a young to middle-aged person with normal vision should be able to see thousands of stars.

Red-lit star party scene beneath starry sky including Andromeda galaxy and big streaks of light to one side.
View at EarthSky Community Photos. | Irwin Seidman captured this image on August 12, 2023. Irwin wrote: “This image is a 9-panel long-exposure panorama looking northward over the Fox Observatory (Bruce Peninsula, Ontario) at the Milky Way and the Andromeda galaxy. While still 2 hours before moonrise, the bright light behind the trees is the glow from the moon creeping over the horizon.” Thank you, Irwin!
How many stars? Vertical cloudy band of Milky Way with light glowing on the horizon and a dark tree in the foreground.
View at EarthSky Community Photos. | Mary Ditchie near Santa Margarita, California, captured this image on August 11, 2023. Mary wrote: “The town of Santa Margarita glows on the horizon through some clouds. The night sky was very clear there and the Milky Way showed up brilliantly next to an old oak tree.” Thank you, Mary! How many stars can you see in the night sky? Good luck counting all those!

Bottom line: Have you ever wondered how many stars are visible on a given night? It all depends on how dark your sky is, what your age is, and other limiting factors.

Visit the International Dark-Sky Association

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Posted 
September 13, 2023
 in 
Astronomy Essentials

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