# Tag Info

35

Barring whatever fantastic energies would be required to stop the mass of the Earth from rotating and then changing the direction of the rotation, one of the major things I can see changing would be the expectations of weather patterns. Part of what affects our weather is known as the Coriolis Effect. While there would certainly be effects from the ...

19

Wikipedia's page about gas giants says so. The paper where the computations are done is arXiv:0707.2895. I haven't read the paper in detail, but the figure you are interested in is figure 4 (p21), where you can see that the maximal size for a planet is roughly 1.5 Jupiter radius, for a planet made of 2000 $M_\oplus$ if hydrogen. Beyond this mass, the ...

18

The day/night cycle is the first obvious effect: Days and nights would both be longer (EDIT Or shorter, apparently I got it backwards) if the speed of rotation is the same. All life on the surface of the planet has evolved for day/night cycles of roughly the length we experience now, with leeway for the difference between summer and winter. A sudden ...

18

The reason being closer to a heat source makes you warmer is the inverse square law. Think of it this way: If you have a $1~\mathrm{m}^2$ piece of material facing the Sun and located at Mercury's orbit, it will be quite hot. What does the shadow of this square look like at Earth's orbit (about $2.5$ times further away than Mercury)? Well, it will be $2.5$ ...

17

Good question! As you guessed, nothing can escape from a black hole, so it is impossible to see one directly. (Quantum field theory does predict that black holes give off an extremely tiny amount of thermal radiation, but it's so little that it we can't detect it from Earth.) Scientists assume that black holes exist based mainly on the predictions of ...

12

Just to put you at ease first, this is not an infantile question. The reason we do not have a solar eclipse at every new moon is mostly due to the angle of Earth's axis (and by extension, the Moon's orbital plane) to the Earth-Sun line. See the picture below for a visual explanation. In the picture, the Sun is to the left. The upper image shows the orbit of ...

12

This animation from UCLA's Galactic Center Group shows stars near the galactic core in images taken from 1995 to 2011. You can clearly see they are orbiting a small and massive object.

11

Do you have an example of this? The most common source of 'rays' is diffraction from the spider - the arms that hold the secondary mirror - in the telescope. There are almost always 4 of these. = If you are using a regular camera there is a weaker effect from the iris - the metal ring that changes size to let more light in. This depends on the number ...

11

Several points that need addressing: The seasons are due to the tilt of the Earth, but not because of the atmosphere. When the sunlight is grazing the ground at a low angle the same amount of heating is spread over a larger area than when the sun is directly overhead, so the temperature drops. The atmosphere has a negligible effect on absorbing radiation ...

9

The effective gravity inside the ISS is very close to zero, because the station is in free fall. The effective gravity is a combination of gravity and acceleration. If you're standing on the surface of the Earth, you feel gravity (1g, 9.8 m/s2) because you're not in free fall. Your feet press down against the ground, and the ground presses up against your ...

9

With the assumptions you have added to the question the answer would be that every ray would end on a star and that the night sky would be as bright as the surface of the average star - i.e. quite bright. You are essentially describing Obler's paradox. Per Wikipedia: In astrophysics and physical cosmology, Olbers' paradox, named after the German ...

9

The Doppler shift in the light from the star tells you the period of the planet's orbit and also the velocity the star moves. You need to know the mass of the star, but this can be estimated to good accuracy from the star brightness and type. Once you know the mass of the star you can calculate the distance of the planet from it's period using:  r^3 = ...

9

The observable universe contains about 100 billion galaxies, each containing on average close to a trillion stars. That is a total of about $10^{23}$ stars. A typical star is like our sun. Sun has a mass of about $2×10^{30}$ kg, which equates to $10^{57}$ atoms of hydrogen per star. A total of $10^{23}$ stars containing $10^{57}$ atoms each gives us a total ...

8

Halley's method requires one to measure the timing of the beginning of the transit and the end of the transit; both pieces of data have to be measured at two places of the Earth's globe whose locations must be known. The picture by Vermeer, Duckysmokton, Ilia shows that the two places on Earth have differing locations in two different directions (the ...

8

Within a few years, it should also be possible to directly observe at radio wavelengths the event horizon of the central black hole in our galaxy. This requires a number of different radio telescopes working together in one big array called the Event Horizon Telescope. If it comes out right, we should be able to observe a "donut" around the black hole which ...

8

The third stages of the first four Apollo lunar missions (8, 10, 11 and 12) were placed in a heliocentric orbit, while those of subsequent missions (13 on) were targeted at the moon. The locations of the orbiting stages are not particularly well known, unless we happen to encounter one, as we did in 2002 when the third stage for Apollo 12 briefly orbited ...

8

Yes. In general relativity and cosmology, the collection of galaxies is often even treated as an ideal fluid, in the thermodynamic sense, with temperature and pressure. The standard textbook on general relativity, the book Gravitation by Misner, Thorne, and Wheeler, discusses this model in Section 27.2, though only on the thermodynamic level. For the ...

8

Planets aren't very easy to spot - 258 known planets doesn't mean 258 planets out there. There is a strong selection effect. Detecting planets based on the movement of a star could only detect very massive planets very close to the star which had a significant gravitational effect. Newer techniques based on a planet blocking some of the stars light are more ...

8

The page to which you linked suggests that the Earth will explode due to global warming. What about Venus? Not only is it closer to the sun, but its greenhouse effect is an order of magnitude stronger than ours. Yet Venus has not exploded. The page also suggests that the Earth's core is some kind of nuclear reactor. It can't be a fusion reactor because the ...

8

The excitement behind various claims is somewhat excessive. First, the Mayan astronomers, see e.g. Mayan astronomy at this page, didn't use any armillary spheres or sextants as others did. Their observations were made with naked eye and they were depicting positions of planets with crosses. The accuracy of the Venus' position after a synodic 584-day cycle ...

8

Oh, but the edge of the atmopheres of Jupiter and Saturn (and the others) are fuzzy! Look at these Cassini images from a few years ago, at the CICLOPS website: "Adrift at Saturn" (PIA 07667), "Beyond the Limb" (PIA 10426), "Off Saturn's Shoulder" (PIA 09791) There is so much gas, such strong gravity, that it gets thicker and thicker quite rapidly as you ...

8

Great question. The electric field creates such a strong force that it would be very hard to move large amounts of just one type of charge. So astrophysical systems do generally eject equal numbers of protons and electrons. In particular, the solar wind is electrically neutral. So these cosmic rays are created in very nearly equal numbers, but by the ...

7

Yes. I'm not going to list all the stars here but it's easy to compile such a list. Wikipedia has a list of exoplanetary host stars. If you sort the table by ascending apparent magnitude and decide how bright "naked-eye stars" need to be, you can take as many as you like from the list by taking all the stars with smaller magnitudes. I think magnitude 6 is ...

7

It all depends on the site you are observing from and the atmospheric conditions (and obviously also on you eyesight). A so-called "magnitude 6 sky" is often taken as the standard for a good dark site with no light pollution. This means that the threshold stars you can see have apparent magnitude 6. According to this article : The farthest star we can ...

7

Surprisingly, it makes no sense to make calculations with the angle subtended by objects. They don't simply "block out" the light of foreground objects. The Universe is more subtle than that and, when you spot a galaxy, in most cases you can be pretty sure that there isn't anything behind it, at least anything that you would be able to see if the galaxy were ...

7

There's some excellent software called Celestia which lets you visualize constellations "from the outside" (among other things). You can easily tell, as you "move" farther away from the Earth, how the shape of the constellations changes. It's truly mind-expanding. They start to change "noticeably" if you go several light years from the solar system. ...

7

which particular observation, made us think that it could be the other way around Retrograde motion must be a prime candidate. As seen from Earth against star background, Mars occasionally slows down and goes backwards. Our moon doesn't. It probably became clear to people constructing orreries that heliocentric models were enormously simpler and more ...

7

It is believed that the planets formed when a cloud of gas underwent gravitational collapse. Any small angular momentum that the cloud started out with has to be conserved, and since the cloud's moment of inertia becomes smaller, it spins faster. Also, the centrifugal force "throws out" the edges of the cloud and makes it more disc-like. As vartec said, ...

6

I agree with the previous answer. Angular momentum, something the earth has because of its rotation about its axis, can only be changed when an external torque (twisting motion) is applied to the earth. As far as I know, there are two ways in which this can happen. If there was friction between the earth's surface and space, then that would slow down the ...

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