41

Because satellites are only visible when they are in sunlight, they are not visible when they go into the Earth's shadow. The app most likely predicts where this occurs and ends the arc. In other words, it does not make sense for an observer to look for a satellite when it is not visible, so there is no need to draw the path when it is in the shadow.


41

Aside from the excellent points made in James K's answer, there are other ways to date craters. For example, when the rays of one crater overlay those of another, we know that the former is younger than the latter. We can also estimate ages of large craters by counting subsequent craters inside the crater floor. Crater counting is one of the more common ...


27

It's brighter on Pluto than you think. NASA developed a tool called Pluto time, which tells you when at your place the ambient light conditions are similar to the ones on Pluto. This occurs when the Sun is only 2° below the horizon! That's quite shortly after sunset, and considerably before the end of civil twilight, which is when it's 6° below. All of ...


24

The "weathering" processes are very slow compared to those on Earth. They are caused by the impact of micro-meteorites and the effect of the solar wind and cosmic radiation on the surface. The solar wind tends to darken the moon minerals. This is why the younger craters have bright rays and the older craters appear much darker. There are a number of ...


13

“No one thought of this,” she said. “We didn’t think of it. The astronomy community didn’t think of it.” What utter nonsense. SpaceX are either lying or they didn't bother to go looking for any other opinions. Astrophotographers have been complaining about satellites messing up their photos for years. When Starlink was announced astronomers complained even ...


9

I was the one operating the telescope at the time! I was using our 11 inch telescope fitted with a 1 MP MallinCam camera. The image was taken at 9:21 pm with a 25 second exposure.


7

Is it possible to create the proposed system of satellites? Yes (in theorey). Hierarchical multiple systems (like the one proposed in the OP) tend to be stable if the periods differ by $\sim 5$ or more and the orbits are near-circular. So, such a system could be stable. A slight problem may be the commensurability of the periods (the fact that their ratios ...


7

Space debris is a big problem for space industry. Natural bodies like dust or asteroids are not the main challenge, although probes are frequently hit by fine dust. The dust causes tiny craters on the surface of the probes or can change rotation or orbit slightly. This can mostly be corrected, e.g. by wheels fueled from solar panels. The most concerning ...


6

Solar flare X-rays travel at light speed, but the solar wind from CME's travels at merely 600 to 2000 kilometers per second. It's the wind that causes aurora and solar storms, depending on the orientation of its magnetic filed. Here's a SOHO view of a CME. It's clear the gas is moving slower than light. You can tell if the earth is in the path of an ejection ...


6

Stars and gases at a wide range of distances from the Galactic center orbit at approximately 220 kilometers per second. From Wikipedia That's much faster than the Voyager probes relative to the Sun (Voyager 1: 17 km/s). Hence the probes will orbit the galactic center roughly the same way as our Solar System, even after occasional hyperbolic encounters with ...


6

Earth's center of mass must be at one of the two focus points of a satellite's elliptical orbit, or at the center of a circular orbit such as a geostationary orbit. One cannot orbit a certain latitude, except for the equator. But there are clever alternatives for different purposes. Geosynchronous (as opposed to geostationary) orbits mean that the satellite ...


6

Chris Peat maintains a very sophisticated database of satellites and their visibilites at http://heavens-above.com, and there is an app available.


5

The Lunar Reconnaissance Orbiter is still up there. At a compact 2000kg, it's likely too small to see via earth based telescope. Mission Page I think the Chinese orbiter is back on earth now, but there may be others.


5

Simple - as you say, in order to get lots of dynamic range in deep astronomical images, you generally need to split your exposure time down into a number of sub-exposures. When you combine these images, you don't just add them up, you "median stack" them (take the median on a pixel by pixel basis) or perform a slightly more sophisticated flux-weighted ...


5

Any binary system produces gravitational waves at twice it's orbital frequency, i.e. with periods of half it's orbital period. So binary systems with periods between 200s and 16000s will produce such waves. We can use Kepler's third law to say something about these: $$ a = \left(\frac{GM}{4\pi}\right)^{1/3} P^{2/3},$$ where $P$ is the orbital period, $M$ ...


4

Do geostationary satellites need to have the equator as the plane of rotation, and the earth's centre to be the centre of rotation? To be stationary above a point, yes. Can it rotate over, say, the Tropic of Cancer, focusing on a single city? If the satellite's orbit touched the Tropic of Cancer, it would not be geostationary since the orbit about the ...


4

A starlike point visibly moving across the sky is a satellite. The biggest and brightest is the international space station, but there are many others. They can be seen any night that is clear, usually shortly after dusk, or before dawn. http://www.heavens-above.com/ allows you to see predictions of when satellites will be overhead.


4

The best way to figure it out would be to use the site "In the Sky" (https://in-the-sky.org/). You can enter time, date and location to identify satellites. This would at least be able to tell you if what you saw was a satellite.


4

I'm treating this as a homework question. You have made a clear attempt, so it is not off topic, but you should clarify the source of the problem. You will first need to establish if the rotation of the Earth is to be considered (it makes a big difference, but in a homework, sometimes the Earth stops spinning!) You have then correctly found the two possible ...


4

I'd caution that absolute statements are not good things in science. When Sagan says a natural satellite cannot be hallow, it is an absolute statement, but there's no way to 100% prove it true. That being said, everything we know about planet/satellite formation tells us that the chances of a satellite forming as a hollow structure (or becoming hollow ...


4

Iridium satellites are known for predictable flare events but are gradually being de-orbited and replaced. In particular, Iridium 66 would have flared at 6:04 several degrees east of Orion, but its orbit has almost certainly changed since its de-orbiting process started on August 2. Other Iridium satellites have taken 3 to 5 weeks to finish this process. ...


4

"The instrument will be tested in Earth orbit for one year, ..." What would it then orbit? It will continue to orbit the Earth, at least for a while. It will eventually end up not orbiting the Earth because it will be placed in low Earth orbit, where orbits decay due to atmospheric drag. The project is a technology demonstrator, which means a limited ...


3

Part (1). Due to the earth's rotation, an observer on the equator moves 180 deg every 12 hours. Your satellite is moving perpendicular to the equatorial plane and it meets the observer on the other side of its orbit after 12 hours. Therefore it too has travelled 180 degrees. To revolve a further 180 degrees (and complete a full 360 degree revolution), in ...


3

These are known as two-line elements (see also nasa.gov, satobs.org). On both lines, the first field after the line number is a NORAD ID, which you can use to query a database such as N2YO. The second line gives geocentric orbital elements for the epoch given in the first line. The last line looks like an error estimate by observation analysis software. The ...


3

Objects in orbit pass over the surface above what's commonly called their ground track. For objects in low earth orbit, though they go around the earth every 1.5 or more hours, the Earth rotates beneath them so they don't trace a simple "circle" over the same points on land. The orbit is around the Earth in a fixed plane, so we are likely (but not ...


3

Small objects in space are hard to detect and characterise. Compare the tesla with another small solar system body: 2015TC25, It is currently about 0.3AU (3/10 of the distance from Earth to the sun) and it has a magnitude of about 30. That is perhaps detectable if you know exactly where to look. It would not be "discoverable" at this distance, with current ...


3

The farthest Orbital Point from Earth is regulated by the fact that at what point the gravitational pull of the Sun overcomes the gravitational pull of the Earth. I found a post for this on Quora This was the most up voted answer by user Paul Olaru on Quora:- Approximately 1.5 million kilometers. It is limited by the point at which the influence of the ...


3

This is for satellites with unknown size and orientation but known standard magnitude (Standard magnitude can be found on the satellite info page of heavens above, the number is called intrinsic magnitude) The proper formula is double distanceToSatellite = 485; //This is in KM double phaseAngleDegrees = 113.1; //Angle from sun->...


3

This has been called "fake news" However tides are caused by gravity, and the proposal doesn't seem to require very massive satellites, hence no tidal waves.


3

The "Artificial Moon" which is being proposed is not nearly as close a copy of the real moon as your concerns suggest. It will be smaller, closer and probably hollow, whereas the real moon is a rather large solid ball of rock quite a long way away. In particular the artificial moon would not be massive enough to exert significant gravity.


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