5 ways our naked-eye views of the night sky deceive us

Observing the night sky consistently produces wondrous feelings of awe.

This image, taken in April of 2025, shows the completed and operational Vera C. Rubin Observatory with its dome open during its First Look observation activities. Overhead, the Beehive Cluster (Messier 41) shines bright, while below, the glow of nearby small cities shines in this mountainous landscape.

Overhead, the Moon, planets, and thousands of stars await.

It only happens once every 11 years, but occasionally, all five naked-eye planets are visible at once. Mercury is always the toughest to spot due to its proximity to the Sun, but sometimes Mars appears even smaller in angular diameter than Mercury. Venus is always the brightest planet, followed by Jupiter, and then usually followed by Mars and then either Mercury or Saturn, although any of those latter three is capable of outshining the others. Under favorable conditions, the much fainter but still technically naked-eye planet Uranus is sometimes visible as well. Here, the Moon is the bright point near Jupiter.

The Milky Way’s plane, plus several deep-sky objects, are often visible.

Although extended objects, like the plane of the Milky Way and a few distant galaxies beyond our own, are identifiable with the naked eye, there are only a few thousand stars that are capable of being seen and resolved with the naked eye. With flawless human eyesight and ideal dark sky conditions, most humans could observe between 6000 and 9000 stars if you could see the entirety of the night sky at once.

But naked eye appearances don’t always match reality.

Behind the dome of a series of European Southern Observatory telescopes, the Milky Way towers in the southern skies, flanked by the Large and Small Magellanic Clouds, at right. Although there are several thousand stars and the plane of the Milky Way all visible to human eyes, there are only four galaxies beyond our own that the typical unaided human eye can detect. We did not know they were located outside of the Milky Way until the 1920s: after Einstein’s general relativity had already superseded Newtonian gravity.

5.) Fully half of all stars aren’t isolated points of light.

This visible light image shows the T Tauri system along with the nearby nebula NGC 1555. Discovered way back in 1852, it is now known to be a young triple star system with a dusty disk of material surrounding the binary component, T Tauri South, which is too extincted to be observable in visible light even with today’s telescope technology.

Many glittering, twinkling stars aren’t singlets like our Sun.

This photo shows the bright, naked-eye star, Albireo. To the naked eye, it appears as just a single point of light. However, a binocular or telescope view shows that it’s actually two very different colored stars separated by a substantial fraction of a light-year: a wide binary system. Even thousands of years after its identification, we still don’t know if this is a bound system, or two stars that happen to be passing one another in close proximity.

50% of stars exist within multi-star systems, but unaided eyes can’t resolve multiple components.

This false-color look inside the star-forming region G333.23–0.06 shows ALMA data of multiple systems of high-mass protostars. Within these clumps of matter, ALMA has found multi-star systems, with singlet stars being a relative rarity. It is only with the spectacular resolution of a modern telescope or telescope array that multi-star components can often be separated within a stellar or protostellar system.

4.) Zero naked-eye stars are of the most common variety: red dwarfs.

The classification system of stars by color and magnitude is very useful. By surveying our local region of the Universe, we find that only 5% of stars are greater or equal to our Sun in mass. It is thousands of times as luminous as the dimmest red dwarf star, but the most massive O-stars are millions of times as luminous as our Sun. Among stars visible to the human eye, many are the rare O and B stars, with no M-class red dwarfs visible at all.

The closest star to our Sun, Proxima Centauri, wasn’t discovered until 1915.

This photo showcases Proxima Centauri: the closest star to our own Sun at present. Although it’s only 4.24 light-years away, Proxima Centauri is not even close to visible to the naked eye, as it’s intrinsically nearly 1000 times fainter than the Sun: typical of red dwarfs, the most common but faintest type of star in the Universe.

About 75% of all stars are faint, cool red dwarfs: too dim for the naked eye.

This graphic compares a Sun-like star with a red dwarf, a typical brown dwarf, an ultra-cool brown dwarf, and a planet like Jupiter. Only about 5% of all stars are like the Sun or more massive; K-type stars represent 15% of all stars, while red dwarfs represent 75-80% (or more) of all stars. Brown dwarfs, although they are failed stars, may be just as common as red dwarfs are, but are even cooler and lower in mass.

3.) Stars’ positions and brightnesses aren’t eternal and unchanging.

The stars that are closest to Earth will appear to shift periodically with respect to the more distant stars as the Earth moves through space in orbit around the Sun. The distances to the stars are so great that it wasn’t until the 1830s that the first parallax, with a 300 million km baseline, was detected. Today, we’ve measured the parallax of over 1 billion stars with ESA’s Gaia mission. The naked human eye cannot detect these changes, even over an entire human lifespan.

Stars move through the Universe just as we do, relative to us.

61 Cygni was the first star to have its parallax measured and published (back in 1838), but also is a difficult case due to its large proper motion. These two images, stacked in red and blue and taken almost exactly one year apart, show this binary star system’s fantastic speed. If you want to measure the parallax of an object to extreme accuracy, you’ll make your two ‘binocular’ measurements simultaneously, to avoid the effect of the star’s motion through the galaxy. Gaia is exceptionally good at characterizing the orbits of nearby stars with small separations from their companion, but faces more challenges with more distant, wider binary systems.

They also vary in brightness and evolve, mostly undetectable by human perceptions.

The Variable Star RS Puppis, with its light echoes shining through the interstellar clouds. Variable stars come in many varieties; one of them, Cepheid variables, can be measured both within our own galaxy and in galaxies up to 50–60 million light years away, with all Cepheid variables exhibiting a relationship between their period, or how long it takes them to reach maximum brightness again after fading, and their luminosity, or how intrinsically bright they are.

2.) Fewer stars are now visible from Earth than ever before.

Under a pristine night sky, the Milky Way’s center casts shadows. As light pollution worsens, nebulosity and stars disappear, until maybe a few dozen stars remain. The numbers 1 through 9 are the Bortle scale, which provides observers with a metric to measure the darkness and clarity of the sky overhead at their location. Only a few locations remain on Earth with pristine, dark skies.

Truly pristine, dark night skies reveal thousands of stars.

This animation changes between two 30-second exposure images taken with the same camera from a protected dark-sky site (at the summit of La Palma, dark) and from a typical modern rural sky (in Washington State near Mt. St. Helens, blue). The difference between the two images, as well as the difference in total sky brightness, is profound.

Light pollution, worsening globally by 9.6% annually, means fewer visible stars than ever.

This map of the world depicts light pollution as a function of geographic location. Every location with a yellow-or-brighter coloring has more brightness coming from the ground than the natural sky, highlighting the severity of light pollution across the world, particularly in Europe, Asia, and the Americas.

1.) Our cosmos is filled with galaxies.

The Milky Way and planet Jupiter shine brilliantly in this photo from the top of Mauna Kea. The yellow glow are the lights from the city of Hilo, located about 25 miles (40 km) away from the mountaintop summit.

Only five galaxies, including ours, are visible to human eyes.

The Large (top right) and Small (lower left) Magellanic Clouds are visible in the southern celestial hemisphere. In reality, the LMC is located some 165,000 light-years away, with the SMC slightly farther at 198,000 light-years. Both galaxies, along with Triangulum and Andromeda, make up the only extragalactic objects visible to the naked human eye, with the Milky Way itself making five total galaxies visible.

But trillions, mostly faint and far-flung, populate the observable Universe.

This comparison image, showing the same region as imaged by Hubble’s eXtreme Deep Field (top) and JWST’s JADES survey (bottom) showcases a selection of many ultra-distant galaxies found in the young Universe. When we observe the Universe at great distances, we’re seeing it as it was in the distant past: smaller, denser, hotter, and less evolved. Back to the limits of JWST’s capabilities, we see evidence for stars and galaxies everywhere.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.