Venus, Saturn and Andromeda Light Up September Skies as M31 Appears 2.5 Million Light-Years Away

Q: Why did a famous 18th-century astronomer completely miss one of the brightest galaxies in our night sky?

Charles Messier likely missed NGC 7331 not because it was invisible, but because it did not cross his path in the way his catalog was built. His list was never meant to be a complete inventory of bright deep-sky objects; it was a practical guide to help comet hunters avoid fuzzy objects that could be mistaken for comets. NGC 7331, a spiral galaxy in Pegasus about 45 to 50 million light-years away, is bright for a non-Messier object at about magnitude 9.25. But brightness alone did not guarantee inclusion. Messier worked selectively, largely from objects he encountered while sweeping the sky for comets from Paris in the late 18th century. If an object was outside his routine search areas, poorly placed seasonally, or simply never examined closely enough under his observing conditions, it could be left out. That helps explain why William Herschel discovered NGC 7331 in 1784, years after Messier had already compiled most of his catalog. Herschel was conducting a much broader and deeper survey of the heavens with different goals and more powerful telescopes, so he was far more likely to pick up overlooked galaxies such as this one. In short, NGC 7331 was omitted because Messier’s catalog was a working comet-hunter’s list, not a definitive catalog of the brightest galaxies. Its absence says more about Messier’s purpose and observing strategy than about the galaxy’s prominence.

Q: Are the companion galaxies of NGC 7331 actually a massive cosmic illusion hiding millions of light-years away?

Yes. At least some of the galaxies that appear to flank NGC 7331 are largely a line-of-sight illusion rather than true close neighbors. NGC 7331 itself is a bright spiral galaxy about 45 to 50 million light-years from Earth. In telescope images, galaxies such as NGC 7335 and NGC 7337 seem to sit close beside it, creating the impression of a tight interacting group. But distance measurements show those two are much farther away, at roughly 310 to 320 million light-years. That means they are background galaxies seen in nearly the same direction, not nearby companions physically clustered around NGC 7331. So the “massive cosmic illusion” is real in the visual sense: the sky compresses depth into a flat image, making unrelated galaxies look adjacent. They are not hiding just a little farther off, but hundreds of millions of light-years beyond NGC 7331. That does not make NGC 7331 scientifically unimportant. It remains the dominant bright member of the NGC 7331 Group and was important enough to be used by the Hubble Space Telescope in calibrating cosmic distance measurements. Astronomers also value it as a Milky Way-like spiral with unusual internal behavior, including a central bulge noted for counter-rotation. For skywatchers, the effect is a reminder that deep-sky photographs can be visually deceptive: objects that seem to be neighbors may actually be separated by vast cosmic distances.

Q: What secret lies hidden within the bizarre, backward-spinning core of the NGC 7331 galaxy?

The hidden “secret” in NGC 7331 is its counter-rotating core: the galaxy’s central bulge appears to spin in the opposite direction from the rest of its disk. Astronomers regard that backward motion as evidence of a violent past. The leading interpretation is that NGC 7331 absorbed a smaller satellite galaxy long ago. Stars from that intruder were likely deposited into the bulge while keeping their original retrograde motion, leaving behind what researchers describe as a fossil record of an ancient merger. That makes the odd core more than a visual curiosity. NGC 7331 is often treated as a Milky Way-like spiral because it is similar in size, mass, structure and star-formation rate, yet this reversed central spin marks an important difference. It suggests that even galaxies that look calm and orderly today may carry scars from earlier collisions and “galactic cannibalism.” Astronomers are still studying the feature, and some details of how the counter-rotation developed remain unsettled. But the strongest takeaway is that NGC 7331’s bizarre inner motion likely preserves the history of a swallowed companion galaxy, hidden in the heart of one of the sky’s brightest spiral systems.

3 articles · Updated · Island Free Press · Sep 2

Venus will shine above the western horizon just after sundown in September, setting shortly after 9 p.m., while Saturn rises in the east at about the same time.
About an hour after sundown, M31—the Andromeda Galaxy—becomes visible roughly 15 degrees above the northeastern horizon and can be seen with the naked eye from dark locations.
At about 2.5 million light-years away, Andromeda is the most distant object visible without optical aid and appears as a faint smudge despite containing about a trillion stars.
September’s lunar calendar may affect viewing conditions: Last Quarter falls on Sept. 4, New Moon on Sept. 10, First Quarter on Sept. 18, and Full Moon on Sept. 26.

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Venus, Saturn, and Andromeda Galaxy Visible in September Night Sky

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🌍 September's sky is full of wonders — from planetary encounters to the Harvest Moon and a change of seasons. ✨ September 2 — Venus appears near Spica in the evening sky.

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Look up! The waning gibbous #moon will rise in the east this evening with golden #Saturn for company. 🌖🪐🌌 For more sky events, visit EarthSky's night sky guide at EarthSky.org. 📸 Chart

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Why did a famous 18th-century astronomer completely miss one of the brightest galaxies in our night sky?

Are the companion galaxies of NGC 7331 actually a massive cosmic illusion hiding millions of light-years away?

What secret lies hidden within the bizarre, backward-spinning core of the NGC 7331 galaxy?

Venus, Saturn and Andromeda Light Up September Skies as M31 Appears 2.5 Million Light-Years Away

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