# Are there more stars in the night sky today? **URL:** \ **Category:** Factual Questions\ **Created:** [April 22, 2018, 3:31am UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889 "2018-04-22T03:31:24Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [April 22, 2018, 7:44pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/21 "2018-04-22T19:44:01Z")
> [@Ponderoid](#): > > Actually there are at least four visible to the naked eye. I knew about [Algol](http://earthsky.org/brightest-stars/algol-the-demon-star) off the top of my head; it’s relatively famous for being an eclipsing binary. [This page includes four.](http://www.skyandtelescope.com/observing/celestial-objects-to-watch/the-top-12-naked-eye-variable-stars/) I couldn’t find any others with a casual search. FWIW, [here’s](https://en.wikipedia.org/wiki/Algol_variable) Wikipedia’s page on Algol variables and it lists 9 of up to 6th magnitude but R CMa would be borderline visible at it’s brightest and not visible at it’s dimmest if you take 6th mag. as the delimiter. YMMV. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [April 22, 2018, 8:56pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/22 "2018-04-22T20:56:24Z")
> [@dtilque](#): > > Stars don’t move that far in only 4000 years, at least not compared with the total distance to that star. Some marginally visible stars may become a little bit less visible and some a smidgen more visible, but things like the darkness of the observing site and the turbulance of the sky will be much bigger factors about whether the star is visible or not. It would definitely be subtle, but that wasn’t the question. If any stars were far enough away thousands of years ago to be just outside of naked eye visibility, proper motion could have brought them just inside that zone. I agree that in practical terms, thing like light pollution would swamp those effects. But strictly speaking there should be some stars visible today that weren’t visible thousands of years ago - and vice versa. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 23, 2018, 4:12am UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/23 "2018-04-23T04:12:29Z")
> [@Sam\_Stone](#): > > It would definitely be subtle, but that wasn’t the question. If any stars were far enough away thousands of years ago to be just outside of naked eye visibility, proper motion could have brought them just inside that zone. > > I agree that in practical terms, thing like light pollution would swamp those effects. But strictly speaking there should be some stars visible today that weren’t visible thousands of years ago - and vice versa. The problem is that there are far more factors about whether a given marginally visible star can be seen at any one time. Besides light polution, the brightness and distance of the star, there’s [ul] [li]whether the star is variable[/li][li]altitude of the star[/li][li]darkness of the observing site[/li][li]turbulence of the atmosphere[/li][li]temperature[/li][li]wind[/li][li]humidity[/li][li]how long the observer has been in darkness[/li][li]altitude of the observing site[/li][li]age of the observer[/li][li]is the observer using averted vision[/li][/ul] And probably several more that don’t occur to me at the moment. Now you might say that you’ll keep all those constant. I’m not even sure you could do that in theory, but in practice you can’t even keep them all constant during a single observation session, or for that matter, from second to second. So there’s no such thing as a simple set of naked-eye stars. However, I suspect the OP is really more interested in those that aren’t marginally visible. For those, the vast majority have not changed their visibility. But besides the “missing Pleiades sister”, there’s also [eta Carinae](https://en.wikipedia.org/wiki/Eta_Carinae). We don’t really know what η Car was like 4000 years ago (it’s too far south for the Babylonians, Greeks, and Chinese to have seen), but just in the past two hundred years, it’s been highly and very irregularly variable. At one point is was brighter than all stars except Sirius, some time later it was too dim to see. It’s currently around 4th magnitude. Much of that variability is due to material the star has expelled. In the not too distant astronomical future, it (or at least one of them; it’s a double star) is expected to supernova. ---
**Author:** ![robz2](https://avatars.discourse-cdn.com/v4/letter/r/5f8ce5/32.png) [@robz2](https://boards.straightdope.com/u/robz2)\ **Post date:** [April 23, 2018, 1:51pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/24 "2018-04-23T13:51:46Z")
In a few years: “Before their meeting the two stars were too dim to be seen by the naked eye, but in 2022, the newly formed Red Nova will burn so brightly in the constellation Cygnus that everyone will be able to to see it.” > **[Spectacular collision of suns will create new star in night sky in 2022](https://www.telegraph.co.uk/science/2017/01/06/spectacular-collision-suns-will-create-new-star-night-sky-2022/)** > > At the beginning of the 3rd century civil war raged in Britain as the Roman emperor Septimius Severus sought to quell unrest in the north. ---
**Author:** ![Sasquatch\_1](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@Sasquatch\_1](https://boards.straightdope.com/u/Sasquatch_1)\ **Post date:** [April 28, 2018, 3:12pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/25 "2018-04-28T15:12:55Z")
> [@Napier](#): > > Not so. Deneb, the head of Cygnus the swan, is a bright star and is 2500 light years away. Eta Carinae, a naked eye star visible in the southern hemisphere, is 7500 light years away. I don’t know what this answer is even referring to. I was assuming the OP meant stars at the edge of the visible universe whose light was just now arriving at Earth, based on the first sentence. ---
**Author:** ![Sasquatch\_1](https://avatars.discourse-cdn.com/v4/letter/s/8491ac/32.png) [@Sasquatch\_1](https://boards.straightdope.com/u/Sasquatch_1)\ **Post date:** [April 28, 2018, 3:21pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/26 "2018-04-28T15:21:35Z")
Quoth Sasquatch: Any new stars you can see now that you couldn’t 4000 years ago would likely just be visible due to relative motion. A star previously occluded by another so not visible, may now be out from behind. > [@Chronos](#): > > Although this does happen occasionally, it’s only with stars that are orbiting each other, extremely closely together, and hence with an extremely short period. Eight hours is a typical number. And all eclipsing binaries are too faint to be seen with the naked eye, and even through a telescope, it’s almost always impossible to resolve them as two separate stars: We only know that they’re eclipsing binaries because of the change in total brightness. > > For stars which aren’t orbiting each other, the size of the star is so small compared to the distances between them that what you’re describing is impossible. Hmm, I didn’t actually go and calculate this, but just threw out that specific example. Intervening dust clouds, two stars lined up that look like one, but 4000 years of proper motion make them visibly separated, it seems there are lots of ways stars can hide. Space is really big though, I admit, so curious what the calculations are for the several thousand nearby, naked-eye visible stars. Are there any that look like 1, but a telescope can resolve 2 (non-binary), or stars with intrinsic brightness that should make them visible, but aren’t due to something in the way outside our or its system? ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [April 29, 2018, 11:44pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/27 "2018-04-29T23:44:48Z")
> [@Sasquatch](#): > > I don’t know what this answer is even referring to. I was assuming the OP meant stars at the edge of the visible universe whose light was just now arriving at Earth, based on the first sentence. From the phrasing of the thread title – ‘stars _ **in the night sky** _’ – I took it to mean "stars visible with the naked eye in the night sky of Earth, which under optimal conditions is said to be about 2000 stars at one time, or about 4000 total. Apologies if I misunderstood. ---
**Author:** ![ExTank](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@ExTank](https://boards.straightdope.com/u/ExTank)\ **Post date:** [April 30, 2018, 3:01am UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/28 "2018-04-30T03:01:24Z")
> [@Lucas\_Jackson](#): > > I’ll have you know _my_ tetrapod ancestors took their first steps bravely and without reservation! [And promptly got hit on the head by a rock.](http://rense.com/general38/crushed.htm) 😛 ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [May 1, 2018, 4:01pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/29 "2018-05-01T16:01:40Z")
Using David Nash’s [Astronexus site](http://astronexus.com/endeavour) (highly recommended for galactic explorers) 61 Cygni, one of the fastest moving visible stars, was at mag. 5.4 four thousand years ago, so still visible even back then. There really aren’t that many stars with high proper motion that are visible with the naked eye, although it may be possible to find one or two very dim ones that fit the OP’s definition. ---
**Author:** ![Slash1972](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/slash1972/32/6461_2.png) [@Slash1972](https://boards.straightdope.com/u/Slash1972)\ **Post date:** [May 1, 2018, 4:38pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/30 "2018-05-01T16:38:13Z")
Sort of a reverse of the question, how far back in time would you have to go before one of the stars visible with the naked eye today stopped being visible to the naked eye? ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [May 1, 2018, 5:22pm UTC](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889/31 "2018-05-01T17:22:16Z")
> [@Slash1972](#): > > Sort of a reverse of the question, how far back in time would you have to go before one of the stars visible with the naked eye today stopped being visible to the naked eye? > [@Asympotically\_fat](#): > > This is a common misconception: where there is a limited absolute viewing distance (the technical term is ‘particle horizon’), new objects are always appearing in the observable universe. This is a fundamental feature of such models, assuming the Universe has an open topology. This of course ignores practical limitations to the observation of distance objects. > > The farthest galaxy currently observed is 13.39 bly away in light travel distance. Assuming an age of the Universe of 13.77 billion years, this means it entered our observable Universe 380 million years ago when our tetrapod ancestors were making their first tentative steps on land. This is in true in the sense that we can see em radiation from this galaxy, albeit heavily red-shifted and via a near-infrared camera on the Hubble telescope, but approx. 380 million years ago it would be theoretically impossible to observe em radiation from this galaxy from the Earth. [Previous page](https://boards.straightdope.com/t/are-there-more-stars-in-the-night-sky-today/812889.md?page=1)