182

Apart from the horizon topic that was already covered by Separatix and Ctouw, they could quickly verify their observation by measuring the angle towards the sun at different points of the planet at the same time). Those angles will, much unlike at home, be almost identical, since they are measured from a plane a large distance from the observed object (the ...


161

Daybreak and nightfall would be spectacular A flat coin shape would have a day face and a night face with sudden transitions because unlike a sphere, it blocks all sunlight with its own shadow, there is no refraction around the sphere. If you start at noon, things would appear quite normal and stay so into twilight as the suns moves lower in the sky. But ...


128

Dust cloud. The star may be residing in a dust cloud with no other stars nearby. This interstellar dust will create a faint nighttime glow, and can be thick enough that no other star's light can be visible on the planet.


83

Given Sweden has a latitude of 60° N and south Africa of a bit over 30° S, you can never see one from the other no matter how high one is and no matter how small the planet is (as long as it still is big enough to allow you to neglect the distance between your eyes and the surface). The Sweden simply rises further away in the hemisphere invisible from South ...


78

1000 times the speed of light means you can visit something 500 lightyears away in a one-year round trip. 5000 lightyears would take a decade and you are still not even leaving our galaxy. In contrast some things that can be observed with telescopes are millions or even billions of light years away. So astronomy would still need telescopes! [Edit, added ...


72

Virtually everything in Mindwin's answer is wrong. The slowest possible approach of the rogue to the earth would occur with a Hohmann transfer orbit, and in this case orbital energies dictate a closing speed of about 3 km/sec. However, this ignores the gravitational attraction between the earth and the rogue, which will boost this closing speed to about 9.5 ...


69

Perhaps their planet is on the inside of a giant Dyson sphere that was created by an ancient civilization. This would be a vast solid shell that surrounds their entire solar system, the inside of which is covered with solar panels in order to collect as near as possible to 100% of the energy output of their sun. Naturally, this would block their view of the ...


65

Horizon effects would be the first signal. As a quick and dirty calculation, the distance to the horizon in miles is half your height in feet. Given their visual range is going to be far greater than that, you have two options, either the world is absolutely vast (even though gravity is Earth normal) or it's flat. They'll quickly realise something strange ...


64

I’m going to address this as a general question about using airplanes to stop meteors, rather than the very plot specific way the question is worded. Nope. For one very simple reason: Speed. Meteors are not the slow moving flaming behemoths of Hollywood. In reality they’ll be moving at or above Earth's escape velocity (11km/s) when they hit the atmosphere,...


60

The primary way to hide something in space is to make it uninteresting. Start with a boring asteroid, made out of silicate rock rather than metals or organic compounds that are worth mining, orbiting somewhere that's inconvenient to reach, but not so inconvenient that people will go there for the achievement. In Earth's solar system, this would be a main-...


60

Mount Kilimanjaro, despite being close to the Equator, has permanent glaciers on its top. This hints toward the solution to your problem: orography! While one hemisphere is mostly flat, with limited elevation and can enjoy the benefit of a warm climate, the other hemisphere is much more mountainous with most of its peaks above the snow line. The ...


56

Plenty. Asteroid A sufficiently violent impact at a time where the resulting debris doesn't intercept the stations orbits would wipe out life but leave people in orbit alive. Volcanic Winter Volcanic activity obviously would not affect astronauts at all. Plague Confined to the biosphere/atmosphere. They should be careful no-one has brought it on board ...


56

Mass panic and fears of the apocalypse Physically? Nothing. There would be no readily discernable physical effect on the Earth or us, its inhabitants. Emotionally and psychologically though, that is a whole 'nother story. It would cause a tremendous uproar. A magic event of astonishing proportions has taken place. As other answerers have pointed out: the ...


55

Your simple answer is that no one has got round to checking that star yet. There are perhaps 2 million stars within 500 light years, of which about 150,000 are G-class like our sun. Corot and Kepler looked for transits on a lot of stars at once, but had fixed fields of view and couldn't scan the whole sky (and Corot couldn't have detected a planet that small)...


53

An Edge Not sure why this has not been said, but when you go for a long enough walk and get to the perimeter of the disk planet, there is an edge. In the Trueman Show it look like this:


53

There is no atmospheric height any object of any size can be, perpendicular to the location of Sweden, that could be seen by anyone standing anywhere in South Africa. I don't need math to prove this. Just take out a piece of paper, draw a circle, and use a ruler to start drawing lines. That combination cannot be done. Alternatively, visit maps.google.com,...


51

One possibility is for the surface of the planet to be covered in highly luminous matter. Perhaps all the surface is an interconnected network of bioluminescent life. There is no moon (assumed because you make no mention) and the high levels of light pollution at night will blot the stars out. You could combine with a naturally hazy atmosphere and cloud ...


50

Yes, you can! You could imagine a universe where physics is based on Galilean relativity instead of special relativity. I'll skip over the mathematical details (unless you're interested), but basically Galilean relativity describes a spacetime that has one universal axis of time, which never mixes with the dimensions of space as it would in special ...


49

Very cool, I'm sure. Roy Prol put together a fantastic animation describing what a Saturn-like ring system would look like from the surface of the Earth: What Earth Would Look Like With Rings Like Saturn Essentially, the rings would most likely be aligned with the planet's equator running from east to west. When viewing the rings directly from the equator, ...


49

A wobbling pulsar will do the trick. Pulsars emit a lot of energy in narrow beams that come from their poles. The slowest ones flash every few seconds; make its tilt wobble so that it is not pointing at the planet all the time. In addition, wobbling causes the pulsar to shoot at different points of the planet's orbit through time. The planet is hit when the ...


49

Combine an significant axial tilt with a elliptical orbit. Axial tilt allows one hemisphere to be in winter while the other is in summer. Earth has approximately 23.44 degrees of tilt. Even in mid-summer the temperature at the south pole is far from tropical because the sun never rises above 23 degrees and sunlight is correspondingly dim. 45 degrees is too ...


47

Yes and no. This NASA page has a good summary of why we have seasons (emphasis mine): It is true that Earth’s orbit is not a perfect circle. It is a bit lop-sided. During part of the year, Earth is closer to the Sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the Sun and summer when it is ...


47

Even with Moon and Mercury out, the rest of Solar system should still be recognizable. Venus, Mars, Jupiter, Saturn and the rest should still be on their orbits, though those orbits may shift a little. Also, Andromeda galaxy would not go away, and while its presence has no relation to Solar system, the distance to this galaxy may serve as a somewhat accurate ...


47

The sky is too big to let only professional astronomers look at it. Consider that professional telescopes have limited time windows for specific researches. And if you want to spot potential hazards for the planet you cannot look once in a while. At least, to watch over my house for theft I would not pay for a guard who looks at it just 1 hour every week. ...


46

The ground worldwide might be rich in radioactive ores, but you have to dig at least half a mile down to find them. However, many plants have roots that do go that far down. Those plants are radioactive. Staying away from them is enough to be safe by day. But, by night, their flowers bloom, releasing radon, a radioactive noble gas. The plants don't ...


45

I would say none or close to none. The main problem is that being in space isn't very different from being in some confined places on Earth (with regard to isolation). For example submarines, some very remote areas, shelters, some deep caves, etc. arctic stations. So, for that (i.e. everyone but those in space die) to happen, it had to either spread over ...


45

Is there a (realistic) way for such a planet to exist? No. The minimum exposure time for such a photo is about 10 minutes (360 degrees in 24 hours means that to have 15-degree arcs you need one hour of exposure; five minutes will yield blurred arcs of less than three degrees). The scotopic retinal persistence (bright lights seen at night) has a relaxation ...


44

Well... I guess they would have to go by the other planets then, the Gegenschein could also help: Gegenschein (German: [ˈɡeːɡənʃaɪn]; lit. "countershine") is a faintly bright spot in the night sky centered at the antisolar point. The backscatter of sunlight by interplanetary dust causes this optical phenomenon. Since you don't mention the tech level they ...


43

As another answerer provided, Neutron stars already do this. So, I'm going to alter my answer somewhat to address whether there are other means by which a star-like object may exist, besides the one we already know about. In that regard, I'm afraid my ultimate answer to this is going to be 'No' or at least 'Not with our current laws and/or understanding of ...


42

Unless all the land mass on the tidally locked moon is on the side facing away from the gas giant, the humans will discover they're orbiting a gas giant during the stone age: If the land mass is indeed concentrated on the far side of the moon only, they will discover it a bit later, maybe as early as prehistory but certainly no later than the invention of ...


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