42 votes
Accepted

How do we distinguish old craters from new ones on the Moon?

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 ...
Dan Hanson's user avatar
  • 1,161
41 votes
Accepted

Why do satellites arcs end abruptly when observed from Earth

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 ...
JohnHoltz's user avatar
  • 7,952
34 votes

Is it possible to have satellites (natural or not) orbit the same celestial object in different directions ? (clockwise, counterclockwise)

It is absolutely possible. Moons that formed with their planet will be in prograde orbits, but moons that are captured bodies (such as the outer satellites of Jupiter, Saturn, Uranus, and Neptune (...
notovny's user avatar
  • 4,770
30 votes

Why can't observatories just stop capturing for a few seconds when Starlink satellites pass though their field of view?

Tl;dr, From personal experience, it’s not worth it. It’s a lot easier to throw away bad data than to try to calculate when stop. There’s not a lot of ambiguity as to whether it messes up the data. As ...
Justin T's user avatar
  • 3,404
28 votes
Accepted

What could be an explanation for a satellite-like moving light in the night sky that dims over time

From your description, this was most likely a Satellite Flare. This is the Sun reflecting off a highly reflective part of the satellite. The most famous type was the flares from the Iridium ...
Greg Miller's user avatar
  • 5,632
25 votes

How do we distinguish old craters from new ones on the Moon?

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 ...
James K's user avatar
  • 118k
24 votes
Accepted

Did nobody in the Astronomy community think 12,000 new satellites in LEO might be a problem?

“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 ...
Aaron F's user avatar
  • 1,632
23 votes

Can a satellite stay in one place but not above equator?

To add to @Planetmaker's concise yet complete answer: In order to keep at least one satellite in the sky over Russia (or any other high N or S latitude area) at all times, the Molniya orbit was ...
uhoh's user avatar
  • 31.2k
22 votes
Accepted

How can the Sun block an X-ray telescope from observing a QPO galaxy "for several years"?

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 ...
ProfRob's user avatar
  • 149k
21 votes
Accepted

Can a satellite stay in one place but not above equator?

No. A geostationary satellite is in an orbit around the earth with a 24 hour period - in the same sense of rotation as the Earth rotates. That makes sure that its orientation with respect to the ...
planetmaker's user avatar
  • 18.9k
19 votes

Is it possible to have satellites (natural or not) orbit the same celestial object in different directions ? (clockwise, counterclockwise)

Partial and supplemental answer. As an example1 from Wikipedia's List of natural satellites; Mooons by primary: (Jupiter's) 84 known irregular moons are organized into two categories: prograde and ...
uhoh's user avatar
  • 31.2k
16 votes
Accepted

How do satellites impede current telescopes?

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 ...
ProfRob's user avatar
  • 149k
16 votes
Accepted

Will Starlink deface the night sky?

Satellites just add moving lights to the sky, they do not obscure stars. However, some may find that disrupting their view of what a sky should look like. The visual magnitude of starlink satellites ...
Anders Sandberg's user avatar
13 votes

What could be an explanation for a satellite-like moving light in the night sky that dims over time

It very likely IS a satellite which is moving from the sunlit part into the shadow of the earth, dimming more and more as it crosses from the day side through twilight (partial earth shadow) to night.
planetmaker's user avatar
  • 18.9k
12 votes
Accepted

Can New Horizons be used to measure the distance to Betelgeuse (despite its fickle photocenter)?

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 ...
ProfRob's user avatar
  • 149k
12 votes

Will Starlink deface the night sky?

A nightmare for star hopping I can only speak as an amateur astronomer with a 10-inch Dobsonian. My telescope has no GOTO or tracking, so if I want to find something interesting in the sky, I have to ...
Eric Duminil's user avatar
  • 1,365
12 votes
Accepted

Did this satellite streak past the Hubble Space Telescope so close that it was out of focus? If so, how close was it?

As you note, that particular image has been identified as due an "out of focus" satellite (the other images presumably show more distant satellites in e.g. geosynchronous orbits). The Nature ...
Peter Erwin's user avatar
  • 16.7k
10 votes
Accepted

Exposure details for this now (in)famous image from Lowell Observatory?

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.
Victoria's user avatar
  • 116
9 votes

What is k2, how does it relate to Io's volcanism and how can Juno constrain its value?

It is called Tidal love number. The definition is as follows: In Newtonian gravitational theory, a tidal Love number relates the mass multipole moment created by tidal forces on a spherical body to ...
Nilay Ghosh's user avatar
  • 4,436
9 votes
Accepted

Is it possible to have satellites (natural or not) orbit the same celestial object in different directions ? (clockwise, counterclockwise)

Wikipedia has some examples of satellites in a retrograde Earth-Centric orbit: Israel has successfully launched seven Ofeq satellites in retrograde orbit aboard a Shavit launcher. These ...
ScottishTapWater's user avatar
8 votes
Accepted

What produces gravitational waves with "periods between about 100 - 8000 seconds"?

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 ...
ProfRob's user avatar
  • 149k
8 votes
Accepted

Fixing satellite eclipse equations from textbooks that are seemingly failing

The issues in each approach stemmed from bad assumptions, lack of source specificity, and badly labeled data. Both approaches were essentially doing the same math, just with different labeling/...
Michael Bonnet's user avatar
7 votes

Did nobody in the Astronomy community think 12,000 new satellites in LEO might be a problem?

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 ...
Barry Jenakuns's user avatar
7 votes

How do radio astronomers avoid having their receivers burned out by ground-imaging radar from satellites?

There are a number of approaches to avoid the impact of radio frequency (RF) emitters in radio astronomy. This interference can impact performance even if it is not at level that is significant to ...
GrapefruitIsAwesome's user avatar
6 votes
Accepted

How do observational astronomers manage streaks and other artifacts from objects in Earth Orbit?

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 ...
ProfRob's user avatar
  • 149k
6 votes

Can a satellite stay in one place but not above equator?

Depending on your definition of satellite; maybe yes. Only over the equator can you have a satellite in a Keplerian geostationary orbit. This idea is covered in depth in other answers. I would note ...
Clumsy cat's user avatar
6 votes
Accepted

What is k2, how does it relate to Io's volcanism and how can Juno constrain its value?

$k_2$ is one of three tidal Love-Shida numbers related to how gravitation of another body (Jupiter in this case) changes a planet-like body's second degree spherical harmonics (Io in this case). Three ...
David Hammen's user avatar
  • 33.7k
6 votes

Will the lunar gateway be visible for ground based (amateur) telescopes?

Will the lunar gateway be visible for ground based (amateur) telescopes? Yes! It will be a bit of a challenge but certainly doable. The Lunar Gateway will be much further away - about a thousand ...
uhoh's user avatar
  • 31.2k
6 votes
Accepted

What was the GPS time at J2000 epoch?

You are correct, and the website is wrong. GPS time is co-moving with TAI, so the simplest way is to calculate everything in TAI: J2000.0(0) = 2000-01-01 11:59:27.816 TAI GPST(0) = 1980-01-06 00:00:19 ...
Teemu Kalvas's user avatar
5 votes

App that shows what's passing in sky?

Chris Peat maintains a very sophisticated database of satellites and their visibilites at http://heavens-above.com, and there is an app available.
rob's user avatar
  • 1,021

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