# Tag Info

42

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 ...

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.

30

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 ...

25

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 ...

22

It is not that it is blocked by the Sun, but that the duration of time for which it can be continuously observed was too small to be useful for the investigations performed in the paper. The object was observed by XMM-Newton, which has a highly eccentric ($e \sim 0.8$), 48-hour orbit arond the Earth. This is designed so that the satellite can stare for ...

21

“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 ...

16

Satellites, even in geostationary orbits, move with respect to the background stars and make "trails" on telescopic images that are tracked at the sidereal rate. Removal of these can be as straightforward as taking the median of a set of exposures. What I mean by this, is that in a sequence of exposures, the satellite trail will pollute different ...

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.

8

In principle yes, in practice no. The telescope is good enough, but the CCD camera will saturate, preventing a good positional measurement. Salient facts. The parallax to Betelgeuse as seen between Earth and New Horizons will be about 250 mas. The current distance uncertainty is ~20%, so to better that, the position of Betelegeuse measured by New Horizons ...

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

What caught SpaceX and the astronomy community off-guard wasn't that the satellites might affect astronomy, it was just how bright the Starlink satellites were. "We all knew the satellites were coming, but we never imagined they were going to be so bright," James Lowenthal, an astronomer at Smith College, Source

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

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

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

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'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

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

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

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 ...

4

Satellites already cause problems for telescopes, but not by obstructing their view. Actually the light reflected from satellites is a bigger problem, and for observations of radio waves, their communications are the really big problem. In terms of reflected light, you might remember the controversy around the "Humanity Star" being too bright. The ...

4

If all you need is a quick and free tool to visualize orbits around earth, websites such as the following might be enough: First, the very simple orbitalmechanics.info, where you can just ignore the "add launch" option: And then, the more artsy Harmony-of-the-Spheres, which can also visualize some other systems. Maybe that already helps.

3

Yes, they can. The ships that visit the ISS often orbit near the station for several hours before docking. Further, there are several satellites that travel in pairs or trios with other satellites. The nearer the satellites are to earth, or the farther apart they are, the more difficult the task of maintaining spatial relationships between the spacecraft. ...

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 ...

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