44 votes
Accepted

Why does the Moon appear gray when passing between the Sun and the Earth?

That's what it really would look like if you were there with DSCOVR. The albedo of the Moon is only about 0.136, about half of the Earth's average albedo. Of course the part with clouds is higher. I ...
uhoh's user avatar
  • 31.1k
43 votes

I saw a short-lived brightening and fading of a light in the sky. Was that a star imploding, exploding or going super-nova?

No. You likely saw a plane's landing lights, a satellite flare or a shooting star (at least something in the atmosphere or low earth orbit). Two main reasons: A supernova lasts for weeks with only ...
planetmaker's user avatar
  • 19.4k
35 votes
Accepted

Why do satellites appear as streaks in telescope images?

Satellites are moving. They are in orbit around the Earth. Satellites in low Earth orbit are moving at about 7000 m/s relative to the ground. You can work out the orbital speed by $$v=\sqrt{\frac{GM}{...
James K's user avatar
  • 121k
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
  • 4,788
29 votes

Why do satellites appear as streaks in telescope images?

Can you explain me in simple words why the satellite in this telescope image appears as a streak? The exposure time is 1 second. This drawing should explain it: (Note: It could be the other way ...
Ilmari Karonen's user avatar
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
  • 5,867
25 votes

Line of lights moving in a straight line, with a few following

Given the date and timing, this could be most like the Starlink satellites in their "stacked" configuration. They are currently in a line, but they will later move to separate orbits. Dr Marco ...
James K's user avatar
  • 121k
23 votes
Accepted

Which Saturn satellite passes closest to Saturn's rings and at what distance?

Pan, Daphnis, and various other moonlets, I would argue, are inside the rings. If you explicitly discount the Encke gap (which Pan orbits in) and the Keeler gap (which Daphnis orbits in) as being ...
Ingolifs's user avatar
  • 4,155
19 votes

Will JWST be as durable as the hubble telescope?

Hubble was in low earth orbit, and was always intended to be serviceable. In fact, the original plan for Hubble was to have the space shuttle carry it down from orbit and take it back up, but they ...
Sean Lake's user avatar
  • 2,946
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
  • 31.1k
17 votes
Accepted

How will Starlink affect observational astronomy?

tldr; some modelling has been done with a lot more to do, but generally the impact of these constellations is fairly negative, but potentially manageable. Ok, there's a lot to unpack here. First ...
Barry Jenakuns'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
  • 19.4k
12 votes

Why does the Moon appear gray when passing between the Sun and the Earth?

I think the confusion comes down to what "brightness" means. In general we don't really measure (either with our eyes or our cameras) the absoloute brightness of objects. Instead we measure the ...
Peter Green's user avatar
11 votes

Why does the Moon appear gray when passing between the Sun and the Earth?

The other answers have pretty well covered the fact that the moon is made of dark gray stone. But I wanted to mention a way that you can verify this on your own with nothing more sophisticated than a ...
Kevin Krumwiede's user avatar
9 votes

How will Starlink affect observational astronomy?

People have been thinking about and a articles have been coming out on this topic. This article states that as many as hundreds of satellites may be visible at once during twilight at certain ...
usernumber's user avatar
  • 17.5k
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
9 votes
Accepted

How can non-earth-orbiting satellite coordinates be obtained by amateurs?

Does a publicly accessible website/API exist that provides the current coordinates for such objects? Yes! There's a pre-launch planning trajectory from ISRO/JPLNAV in the Horizons system. Chandrayaan-...
PM 2Ring's user avatar
  • 14.4k
8 votes

Why don't we use the Voyager/Pioneer etc space probes to measure stellar parallax?

The basic reason is that Voyager and friends have cameras optimised for imaging planets, not for doing very precise astronometry. So why not send a telescope, like that on Gaia, into interplanetary ...
James K's user avatar
  • 121k
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

Why do satellites appear as streaks in telescope images?

A relatively simply way to remove the streak is to take two-or-more photos, with a short pause between them. The stars won't move much in that time, but the satellite will have drawn a short dash on ...
Criggie's user avatar
  • 183
7 votes

Could a rogue comet perturb a frequently occurring meteor shower to the extent that debris falls on Earth...and dislodges satellites?

Could it perturb? No and yes. Meteor showers are made of meteroids in orbit around the sun, and the gravity of everything affects them, by the law of universal gravitation. But the meteors orbit in ...
James K's user avatar
  • 121k
6 votes
Accepted

How many (or percentage) satellites of Solar system planets have their orbits synchronized like the Moon (always facing earth)?

This is not really known; while the rotation period of most of the larger satellites is known, and they're mostly synchronized, for the smaller ones it's harder to determine and they're less likely to ...
Glorfindel's user avatar
  • 4,790
5 votes
Accepted

Magnitude, satellite flare and the Heavens Above app

The astronomy "magnitude" scale works backwards: smaller numbers indicate brighter objects. Back in the days before precision measurements of brightness, stars were categorized by eye, with the ...
Mark's user avatar
  • 3,393
5 votes

Computing orbit positions of Jovian Satellites / Moons using JPL data

An excellent book by Jean Meeus, "Astronomical Algorithms", provides the calculations for planetary positions and Jupiter's Galilean Moons (Io, Europa, Ganymede, and Callisto). Meeus does not really ...
Aloft's user avatar
  • 91
5 votes
Accepted

How come the Sun does not make the Moon crash on the Earth?

The Sun's gravity does perturb the Moon's orbit but more subtly than you imagined. The Moon's perigee and apogee migrate eastward in an 8.9 year cycle called apsidal precession. Also the plane of the ...
Mike G's user avatar
  • 18.7k
5 votes

Satellite?? Star?? I am puzzled over what I just saw

tl;dr, Like Aaron F mentioned in the comments, this is likely a drone. Let’s consider why it probably isn’t anything else. The nearest star to us, Proxima Centauri, is located 1.3 parsecs away from us....
Justin T's user avatar
  • 3,404
5 votes
Accepted

Contamination problem data

Your teacher means that when you look at the light from a star in the data from a space-based photometry mission like Kepler or TESS, you cannot be immediately sure that any variability seen is from ...
ProfRob's user avatar
  • 152k
4 votes

Why do some artificial satellites decrease and increase in brightness multiple times?

It is exactly the rotation of a space object (satellite or space debris) combined with unequal light reflection ability of its surface parts which makes its brightness rapidly vary over time no matter ...
SergiusPro's user avatar
4 votes

Group of satellite like objects moving through the sky in a formation

Definitely a UFO - Unidentified Flying Object, not necessarily aliens :-). A few possibilities I can think of (would be nice to know how fast the objects were going, and whether or not they ...
Jonathan's user avatar
  • 4,385
4 votes

Please help explain this unknown light in the sky. Not ISS. Not a star or comet. Too slow

That sounds like a high altitude nonfunctioning satellite to me. For example, a rocket body or upper stage that is tumbling. I have seen these types of satellites flash many times before. The ...
JohnHoltz's user avatar
  • 7,982

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