When Neil deGrasse Tyson went to the Joe Rogan Experience, he told the story of how he noticed the sky was wrong, and also the left side was a mirror reflection of the right side.

To know the sky you need to know the date, the time and the coordinates. I'm aware Tyson knows his stuff, but not sure how can have that information on the top of his head.

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    April, North Atlantic, night.
    – hobbs
    Commented Dec 12, 2022 at 4:22
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    "the left side was a mirror reflection of the right side." is kind of a giveaway that the sky was wrong, even if you didn't know the date or coordinates. Commented Dec 12, 2022 at 10:52
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    also , there are stars you only see in one part of the year if you're far enough north or south, with the orientation of earth shifting with the seasons. So there could well be obviously wrong constellations just knowing the month.
    – Mike M
    Commented Dec 12, 2022 at 12:12
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    @hobbs: even "North Atlantic" is more specific than it needs to be. "Northern hemisphere, middle latitude" is probably enough to spot the obvious problems. (Though you might also want to say "middle of the night" rather than just "night".) Commented Dec 12, 2022 at 12:54
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    I hope that we get an answer describing what was actually wrong with the sky in Titanic. Was the sky correct except that one half had been replaced with a mirror image of the opposite half? Was it a view of the sky from the wrong latitude? Or the wrong time of year? Or maybe the star pattern was totally made up and didn't resemble any part of the real sky? Commented Dec 12, 2022 at 17:57

4 Answers 4



In the Northern Hemisphere, one obvious check is that the North Star should be visible, and its elevation should indicate the latitude of the observer. This is true for any location, any day of the year, all night long. In the Southern Hemisphere, the Southern Cross can be used for orientation.

If the North Star is right above you, you're at the North Pole, if it's very close to the horizon, you're close to the equator.

The Titanic sank at ~42°N, which means the North Star should be roughly half-way between the horizon and the zenith.

Neil deGrasse Tyson probably has a good idea of what the sky looks like from any point on Earth, during any season at any time of the night, but on top of that, he lives in NYC, which is very close to ~42°N. Which means that the sky from NYC will be almost exactly the same as seen from the Titanic (+ light pollution). As mentioned by @DarrelHoffman : "New York City was the Titanic's destination, so it's not at all surprising that it would be at around the same latitude. "

Here's another video with Neil, about the stars of Titanic: stars of Titanic youtube video

James Cameron apparently fixed the scene, by the way.

Season & time

The North Star is the center of a celestial clock. Every star seems to rotate around the North Star. Depending on the position of Cassiopeia, the Milky Way or the Guardians of the Pole, it's possible to determine the season or the time of night.

polar star clock

Month, time of night and position of this clock are all linked together. If you know two of them, you can easily calculate the third one.

Obvious fake is obvious

@CrisLuengo posted a gif from the original movie:

original sky from Titanic 1997

This sky looks obviously wrong for any location and any time. Such a bright, conspicuous and symmetrical asterism in the middle of the picture would be very well known. It isn't.

It looks a bit like Corona Borealis. But Corona Borealis is one-sided, and far away from the Milky-Way.

Also, what's weird is that the stars appear to be mirrored, but the Milky Way isn't:

mirrored Milky Way

Bright planets sometimes create short-lived asterisms, but Jupiter & Saturn would appear brighter than the surrounding stars.

Updated version

The updated version looks like this:

updated version

The summer triangle is clearly visible, which is to be expected late at night during Spring. Cassiopeia is also visible, in the bottom-right corner.

Sadly, it appears that Neil deGrasse Tyson forgot to include Jupiter in the modified version. Jupiter should have been the brightest point in the shot.

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    I think this answer does the best job of pointing out that the night sky doesn't change tremendously from one night to another, so you just need the approximate time of year. And that it's always a window on a bigger picture, not a totally separate image to memorize / recognize for different times of year. A few litmus tests can let you recognize that something's not right, if you know some major things that should be in the sky for a general time of year. Commented Dec 12, 2022 at 16:59
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    "all night long"? It's all day long as well, if you can see it...
    – Aron
    Commented Dec 13, 2022 at 5:14
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    That make sense. If sky doesn't change that much and Tyson live on the same latitude, make much easier to detect the wrong sky. Commented Dec 13, 2022 at 6:28
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    Worth noting that New York City was the Titanic's destination, so it's not at all surprising that it would be at around the same latitude. Commented Dec 13, 2022 at 17:27
  • @DarrelHoffman: That's a good point. Still, I was somehow surprised that the latitude was so low. Probably because of the icebergs and because I'd expect the Titanic to sail on a great-circle route between UK & NYC. 42°N is the same latitude as Rome, which I don't associate with icebergs. Commented Dec 13, 2022 at 21:25

The guy's a world-renowned astrophysicist, he's the director of a planetarium… you know, one of those exhibitions that shows detailed imagery of the night sky for the edification of 'you & me', the great unwashed.
Why wouldn't he immediately recognise the sky was wrong for that part of the world/time? [BTW, a hundred years is not going to change the star map appreciably to the naked eye - you need thousands to be able to overlay two maps & easily spot the difference.] It would be like you & me recognising some writing was mirror-imaged… or in French. Even if we know what the Great Bear looks like, we wouldn't have a clue where it should be or at what time; we'd just have to gaze around & maybe we'd find it… or not.
Some people do. It's their job. To them it's like looking at a clock & recognising what time it is - or to extrapolate, also immediately knowing what time that makes it in Tokyo, London & Los Angeles.

Put it another way - would you spot immediately if someone showed you a picture of some random hand & claimed it was yours? There's some mileage in the term 'knew it like the back of his hand.'

There are many versions of this tale online, some variation on a theme of "You got it wrong" "Well, let me know what it should be like & I'll change it." It really becomes news because he actually did change it in recent versions. Here's one of the many news items about it - How Neil deGrasse Tyson Got James Cameron to Edit Titanic—15 Years Later which doesn't disagree with your video, merely details it slightly differently.

Long and short, if you actually know what the sky should look like, you'll spot it immediately. For you & me - who cares, we'll never, ever notice.

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    You wouldn't really care even if you got told what the difference was. I'm in IT and I constantly complain why IP address of can't exist or that hacking into is stupid, but people just roll their eyes and call me a big nerd.
    – Nelson
    Commented Dec 12, 2022 at 1:52
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    @Nelson Looks like your IP is in octal.
    – Déjà vu
    Commented Dec 12, 2022 at 10:17
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    Same reason how astronomers before photography were able to spot (super)novea: they knew the sky so well that even a single bright wrong star would be recognizeable as "new" to them.
    – PlasmaHH
    Commented Dec 12, 2022 at 10:31
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    @Nelson honestly I'm in IT and I'd roll my eyes too; it's just the internet version of a 555 number. (Yeah, I know there's an official range meant for that, but still.) Why not just assume that in the universe of whatever show or movie that RFC 790 was slightly different or something? :P
    – Idran
    Commented Dec 12, 2022 at 16:45
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    @Nelson if you think working in IT is bad, don't get me ( a physicist) started about any action or sci-fi movie. Commented Dec 12, 2022 at 21:28

I don't know specifically how Neill deGrasse Tyson would spot an inacurate depicting of the night sky at a specific time and place. But everyone has different areas of epertise and knowledge.

Everyone has areas of expertise and things which they can immediately recognize. For example, most people can recognize faces very well and can recognize thousands of different people they know or have seen pictures of. And people who don't know someone might not be able to recognize them or pick them out of a police line up after seeing them only once.

Added 12-172022. Here is a link to an image of a sculpture:


The site with the image identifies it as Helen of Troy, as do some others. So take a look and see if you think it is beautiful enough to be the legendary beauty of Greek myth.

Actually it is not a sculpture of Helen of Troy, it actually depicts a man, Helen's husband Paris. I recognized it from seeing it correctly labeled. And even someone who doesn't know who it represents could tell it wasn't Helen, knowing enough about art conventions. The Phygian cap was only worn by Trojan males in Greek and modern classical art, showing that it can't be a woman. And a trojan male with such a cute face could only be Ganymede or Paris.

Many people have strong memories for odors. I imagine that a chef walking into a kitchen could correctly identify all the ingredients being used while someone like me would only notice "cooking odors".

Sometimes I smell something outdoors which reminds me of a walk I took in a specific place look ago. And someone who knows plants in the region could probably identify that smell which is a mystery to me.

End of 12-17-2022 additon.

Photographer Camillius S. Fly took many photographs during the peace conference between General George crook and the hostile Chiricahua Apaches in March 1886. Probably the most famous shows many participants seated on the ground in a sort of a U shape. Here is a link to an online copy:


And after seeing it in various books, I noticed there were actually two almost identicaal photographs which must have been taken mere minutes apart. I guess Fly wasn't satisfied with the first one, and took another one he liked better.

The most often seen version shows Geronimo better, which is why it is most often used. And that means that the boy seated at the far right of the photo, Charles DuVal Roberts, had to put up with seeing that version of the photo for the rest of his life, eighty years, despite him having a rather goofy exprssion in that version.

And that is the kind of detail someone can notice when they become familiar with a subject.

I once noticed that a room in a television commercial looked like the ante room at the mansion Syon Park in England. And the opening of the Sherlock Holmes comedy Without a Clue, 1888, was filmed in the ante room at Syon House, which was supposed to be some sort of government office in London. And when the characters left that government office the exterior was the courtyard at Blenheim Palace, the residence of the Duke of Marlborough, tens of miles from Syon Park and from London.

I often recognize real buildings used in movies, which are often used to represent fictional buildings tens, hundreds, or thousands of miles away from the real location of the real buildings.

Here is a link to a discussion of mansions used for exterior shots of fictional mansions called "Hill House".


And here is a link to a discussion of a mansion which has been seen in many different movies and tv shows.


And many people who have no interest in architecture would never recognize many of the buildings I recognize.

The Bunk'd episode "Serf's Up-Rising", November 23, 2019 was set during the annual Renaissance Fair at the fictional Camp KIkiwaka. One of the decorations in the mess hall was a flag which looked much too modern to be Medieval, or even Renaissance. It looked like a reproduction of an Austrian military color with the coat of arms of the Elected Emperor of the Romans, ruler of the Holy Roman Empire and of all the Austrian lands.

As I remember, the halos around the heads of the eagle, and the coats of arms on the torso of the eagle indicated it was the 1792-1804 pattern.

And people who weren't interested in flags, heraldry, etc. wouldn't recognize that flag or know why it was anachronistic as a decoration in an Renaissance Fair.

Added 12-17-2022.

Hundreds or thousands of movies and tv shows have been set in real communties. And in each case moviegoers or tv viewers who actually lived there would have different opinions about the depictions of their homes than the vast majority of the viewers.

For example, Apaches who live on the Fort Apache Indian Reservation in Arizona will sometimes have seen western movies like Fort Apache (1948), Taza Son of Cochise (1954), or tv shows like The Adventures of Rin Tin Tin (1954-1959. Those productions depicted Fort Apache in scenes filmed at the Corriganville Movie ranch near Los Angles, California, at Monument Valley on the Utah-arizona state line, and at the Kanab Movie Fort in Knaab, Utah. And I think those locations actually look quite different from the neighborhood of the real Fort Apache.

I know a bit about Jenkintown, Pennsylvania, where I lived for almost seven years. And as it happens, there is a tv show, The Goldbergs (2013-) set in Jenkintown during the 1980s, (which was not when I lived there). It is loosely based on the teenage years of Adam Goldberg and his family.

Wikpedia says:

Many references to real-life Philadelphia-area businesses are made, including the Wawa convenience store chain, Gimbels department store, Willow Grove Park Mall, and Kremp's Florist of Willow Grove, Pennsylvania.


But in the few years I have watched The Goldbergs I never noticed anyone mentioning watching movies in the Hiway Theater in Jenkintown or the Keswick Theater in nearby Glenside.

I noticed that during the seasons which I have watched, the producers saved money by never filming establishing shots of any actual buildings in the Jenkintown area. Thus I have never seen my home away from home when I lived in Jenkintown, the Abington Library, or Alverthrope Park, or any other sights in the area. Instead the exteriors of all buildings were filmed in the Los Angeles area. On one website someone commented that if you looked closely you could sometimes see palm trees in the background of exterior shots.

So how much do the exterior shots of the William Penn Academy look like the real William Penn Academy where the Goldberg kids went to school?

The William Penn Academy is fictional. The real Goldberg kids went to the William Penn Charter School, founded in 1689, at 3000 West School House Lane in the Germantown neighborhood of Philadelphia. That is over seven miles from their home at 405 Newbold Road, Jenkintown, so the real Goldberg kids had quite a commute to school.

There is another Quaker school, which is in Jenkintown, the Abington Friends High School at 575 Washington Lane, founded in 1697. And some episodes of the Goldbergs indicate that the fictional William Penn Academy is in Jenkintown, like Abington Friends.

And the vast majority of viewers of The Goldbergs who never lived in Jenkintown might never think about how realistic the show is, or even wonder whether Jankintown is a real or a fictional place.

The Tony Randall Show from 1976 to 1978 had an opening each week where the camera zoomed in on a window of the monumential Philadelphia City Hall, suppsedly the window of his character's office. And of course some people who worked in Philadelphia City Hall at that time would know what was behind that window, while most viewers wouldn't even know whether the building used in that scene was actually in Philadelphia or Los Angeles.

I have watched a lot of western movies. And I note that some fans of western movies know a lot about old guns and can recognize the prop guns used in movies much better than I can, and tell if they are anachronistic for the fictional dates.

Here is a link to a thread about The tall Men (1955):


The OP asks:

Why did they set the film in 1866 then outfit everyone with 1873 Colts and Winchesters? They could have just as easily used correct percussion guns.

The prop guns used in a movie were probably selected by the prop master and selected for being cheap to obtain and not being too many years anachronistic. Probably the main movie makers usually consider the props used to be a minor factor.

The date of 1866 seen in an opening title card would have been decided by the writers, director, producer, and other creators of the film and thus is a more important part of the film than the prop guns used.

The plot involves a cattle drive from Texas to Montana. The last segment of the cattle drive is along the Bozeman Trail, where they are attacked by hostile Sioux. The Bozeman Trail was used by travellers from 1864 to 1868, and then closed until 1877, and travelers along the Bozeman trail had a high probability of being attacked by Sioux during Red Cloud's War from 1866 to 1868.

So the 1866 date establishes that the film happens during the period when its events could possibly have happened in the history of the west.

Apparently I am more knowledgeable about events in western history than most fans of western movies, while many fans of western movies have much greater knowlege of 19th century guns and can recognize them much better than I can.

End of addition 12-17-2022.

I have seen many crime shows where a automobile is described with the make, year, etc. in police bulletins, and even in episodes where I have had good views of the car used in the crime, I couldn't describe its model, manuacturer, or year like the characters do because I little interest in automobiles.

Different people have different areas of interest and expertise.

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    <points at TV> Those stairs aren't built to code.
    – Mazura
    Commented Dec 12, 2022 at 1:14
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    One of the most famous musicians in my country recently shot the music video for one of their songs in my town. It's not often that an artist of his level comes around here. When I (or another person from my town) look at the video, I spend the time saying "oh, this is here and that is there, and that one is not actually a bank!". Everybody else in the world just listens to the song and follows the clip's story, and does not care whether that is actually a bank.
    – Simone
    Commented Dec 12, 2022 at 9:34
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    Me: "he's not actually playing that saxophone."
    – RedSonja
    Commented Dec 12, 2022 at 13:47

To spell out an aspect of this question that hasn't been directly answered ... Orbital Astrophysics is extremely well understood, and completely deterministic.

We have an enormous repositories of measurement data about where celestial bodies are now, and have been for the past 50+ years, which means we know exactly how they are moving now.

From their current position and movement it is conceptually trivial to extrapolate their positions forwards and backwards through time. The physics of that interaction is just very simple.

It's marginally more effort for the computations to be done, for parts of the astrophysical systems with lots of bodies interacting, but only barely, and for visible stars that effort has been done some time ago.

So it's an entirely solved problem, to answer the abstract question "at this point on earth, on this date ... what would the night sky have looked like?".

The other questions address how an individual could recognise such a discrepancy unprompted.


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