To check to see if we have an extra sun or an extra easy to see bright object in our daytime sky next to the sun, as these enthusiasts for “Nibiru” claim to have videoed or photographed - try looking with naked eye. Don’t look at the sun, it’s right to warn not to do that as your eyes are easily damaged by UV light especially and your retina has no pain sensations and you won’t notice until maybe hours later if you stare at the sun for a long time and it does get damaged and you find a dark spot in your vision.
Instead, put your finger in front of the sun so that your eyes won't be damaged by the sunlight. Then look to left or right, above or below - do you see a second sun or anything else? If not, you have disproved all those videos that claim there is a bright object next to the sun in the sky. A star or planet can’t appear just to some people and not to others. It can be hidden by clouds yes, but if you have a clear blue sky, there is nowhere for it to hide at all, if there is a big bright object anywhere there, just block out the sun with your finger and you’ll see it.
It's bound to be something to do with the camera. They aren't designed for photographing the sun directly, and the bright light overwhelms the lenses and CCDs and you get lens flares and ghosting.
If you have a lens cover of some sort or photograph through glass, you are likely to get an offset lens reflection as well.
The only astronomical things we see with naked eye are the Moon of course, often in the sky at the same time with the Sun, daylight comets (but those are very rare and we don't have one at present), occasional fireballs - they are rare for individuals - you are very lucky to see one but worldwide they are quite common, but flash across the sky and are gone in a few seconds . Then if you know exactly where to look, you may see the planets Venus and Jupiter but those are not at all obvious - you need to know exactly where to look and sometimes on clear days when they are in the right position you see a white dot the same brightness of the sky, tiny white dot against the blueness of the sky. You can easily look straight at it and see nothing and it is very hard to photograph.
There are a few other possibilities which a few of the videos may show. Drones. Parachutists descending at night with lights. Rocket launches. A silvery child’s helium balloon catching the light of the sun. A weather balloon lit from behind by the sun. In the case of photographs from the ISS - dirt on the windows. The ISS windows get dirty and need to be cleaned from time to time, except they have to use spacesuits to clean the outside of the ISS windows.
A surprising number just show the sun lighting up clouds. Many people are so little aware of the sky that they may never have noticed this until someone tells them to look for “Nibiru”. I also often get pms from people who notice the Moon rises at a different time each day, sometimes in daytime, and get scared by this. The Moon has done this all their life, but they never noticed before.
If an amateur astronomer discovers even a new comet, then that is the astronomical highlight of their lifetime, and there are hundreds of thousands of amateurs, maybe millions.
A new planet inside our solar system, with an orbit that comes inside of Uranus, never mind Saturn and Jupiter, is impossible, because its orbit would be unstable. But were such a thing possible and someone spotted it, they would be instantly the most famous astronomer in planetary science, their career would be made, they might even get a Nobel prize. There is no way astronomers are keeping such a thing secret and do you think the astronomers don't have the ability to take photographs with consumer cameras?
But it’s not possible. Such an orbit is so unstable, passing by the “wrecking balls” of Jupiter, Saturn, Uranus and Neptune every orbit, that within a million years it would be gone, either hit one of them, or deflected into another orbit to hit the Sun or be ejected from the solar system. The gravitational influence of those planets extends quite a way beyond the physical planet. It is possible for a planet to stay in resonance with Neptune. Indeed Pluto does exactly that, it does two orbits of the sun for every three orbits of Neptune. But Uranus is not in any nice ratio of orbital periods with Neptune so it is impossible for a planet to stay in resonance with Uranus and Neptune simultaneously. So no planet can stay long in an orbit that crosses both Uranus and Neptune’s orbits. Add in Saturn and Jupiter as well, neither of them in resonance with any of the others either, and you end up with an orbit that is unstable within a million years.
This means that if a planet was in a “Nibiru” like orbit at the time of the formation of our Moon, then it was already gone 4.5 billion years ago.
So a planet in a “Nibiru” type orbit is impossible. Extra planets are possible. Neptune was discovered as an extra planet in the nineteenth century beyond Uranus. Pluto was discovered in the twentieth century beyond Neptune (but crossing to inside of Neptune occasionally). We could find new planets even further out beyond Pluto. But we can’t find new planets that come inside of Uranus’ orbit. We do find new dwarf planets that come inside of Neptune’s orbit, the “Trans Neptunian Objects”. But a large planet, just to be not discovered yet would have to be way way beyond Neptune.
“Planet X” is not a single object. “X” stands for unknown and any hypothesis for a new planet is called “Planet X” by astronomers. So they have been searching for “Planet X” since the start of the twentieth century. Pluto was the first “Planet X” and the only one to be confirmed. Since then, nearly all the other hypotheses for “Planet X” have been disproved. We do have a couple of possible hypotheses still. Nemesis and Tyche have been almost completely disproved by the WISE search. If they do exist then they orbit a long way away. Nemesis would be 1.5 light years away and yes, it could send more comets our way, but what the conspiracy theorists leave out or don’t dwell on is that that prediction was for 14 million years into our future, not next month or next year. But Nemesis probably doesn’t exist. If it does it is a very cold brown dwarf, unusually cold as WISE found normal brown dwarfs ten light years away. That’s possible but such an unlikely situation that I think most would say that Nemesis doesn’t exist. It’s the same for Tyche.
The main candidates at the moment are the so called “Planet 9” (awful name I think myself but we are stuck with it for now) and perhaps the ”Kuiper cliff” object is still possible. Mike Brown also has a probability argument that there probably are objects at least as large as Mars or Earth out there based on the number of dwarf planets we have so far smaller than that. See Planets beyond Neptune - Probability
These are different hypotheses. But both orbit way way beyond Neptune if they exist.
If you are still scared of “Nibiru”, see also this recent interview with the astrophysicist Brian Koberlein, professor at Rochester Institute of Technology, where he fields questions about “Nibiru”.
See also: Planets beyond Neptune - Wikipedia