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98 votes

Does it make any scientific sense that a comet coming to crush Earth would appear "sideways" from a telescope and on the sky (from Earth)?

The comet's tail always points away from the Sun. Yes, even when the comet is heading back into the outer solar system. This is because the tail isn't a 'trail' of where the comet has been, like a ...
Ingolifs's user avatar
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66 votes

Is pinging the Moon with a laser as shown on "The Big Bang Theory" possible?

There is a very nice Myth Busters video about bouncing a laser off the Moon linked below. To answer your question, current work is done with an array of corner cube reflectors on the Moon roughly 50 ...
uhoh's user avatar
  • 149k
37 votes

Is there any way that real stars would move like they do in the classic Windows 3.x screensaver if traveling through space at extreme speed?

I do disagree with the other answers, not on the result, but on the reason. You don't need to go faster than the speed of light to pass through multiple stars in a few seconds. Putting aside the ...
lvella's user avatar
  • 471
36 votes

Is pinging the Moon with a laser as shown on "The Big Bang Theory" possible?

The University of Texas's McDonald Observatory performs laser measurements of the distance to the Moon using retroreflectors left by the Apollo astronauts. You can read all about it in the McDonald ...
Organic Marble's user avatar
15 votes

Does it make any scientific sense that a comet coming to crush Earth would appear "sideways" from a telescope and on the sky (from Earth)?

While those movies probably do it because that's how comets are commonly depicted, it might not be that inaccurate. Remember that the Earth itself is moving around the Sun, so if a comet is heading ...
Pitto's user avatar
  • 1,196
15 votes

Does it make any scientific sense that a comet coming to crush Earth would appear "sideways" from a telescope and on the sky (from Earth)?

If you're the comet, the way to hit Earth is not to head directly for it. That's because Earth is orbiting the sun: you need to aim at where Earth will be, not where it is right now. For example: By ...
Phil Frost's user avatar
  • 1,033
14 votes
Accepted

Why is there no microscope on the Mars 2020 rover?

The MAHLI camera of Curiosity may focus from infinity down to only 18.3 mm working distance. At minimal distance the resolution is 13.9 µm per pixel. It may image objects of some tens of meters in ...
Uwe's user avatar
  • 48.9k
14 votes
Accepted

First LED left on another planet⁺ by humans?

July 20, 1976, Mars, Viking 1 lander. In the article "Viking gas chromatograph–mass spectrometer" by Rushneck et al, Review of Scientific Instruments 49:817-834 (1978), section G (pp. 828-9) ...
Camille Goudeseune's user avatar
10 votes
Accepted

What is the "space grease" used to lubricate the ISS robotic arm? What are the material considerations for it?

The lubricant is a Braycote vacuum grease: Braycote 602-EF. There is good information on the Latching End Effector (LEE) lubrication task (the task that actually applies the grease to the Space ...
Organic Marble's user avatar
8 votes

How fast do optical surfaces get dirty or damaged in space?

In addition to the space weathering phenomenon described by ebv, optical surfaces can and do get dirtied by other mechanisms as well. In particular, outgassing from the rest of the spacecraft and ...
Terrance Yee's user avatar
  • 2,264
8 votes

First LED left on another planet⁺ by humans?

The Vega 1 balloon that entered the atmosphere of Venus on June 11, 1985, had LEDs on the anemometer: The diameter of the rotating anemometer was 25 cm. The rotor was mounted on ball bearings, and ...
called2voyage's user avatar
  • 23.7k
8 votes
Accepted

JWST - pick-off mirrors?

A pick-off mirror is a mirror that takes light from the telescope's common optical path and directs the incoming light to a specific instrument or sensor. There are two use-cases for them (at least as ...
Ludo's user avatar
  • 14.2k
8 votes

Interesting diffraction pattern on JWST composite false-color image released today (July 11) at Biden preview - how does this arise?

The James Webb Space Telescope website has a very detailed info graphic with explanations that explain the diffraction patterns. As far as I understand, the large blueish spikes in the image in the ...
DarkDust's user avatar
  • 12.5k
7 votes
Accepted

Why does Unity look transparent?

Much of the Unity spacecraft appears (almost) transparent in this image; you can see the blue sky right through it. This is absolute nonsense; you cannot see the sky through Unity's airframe. It is ...
Russell Borogove's user avatar
7 votes

Data rate in optical free space communication systems

You need to look carefully at how it's measured. One of the major contributors to data rate is availability: with low Earth orbit satellites they might only have a few minutes of downlink opportunity ...
Polar_Bear's user avatar
5 votes

Have optical zoom systems been used in space exploration?

The video camera on the Apollo LRV had zoom, used in the well-known Apollo 17 liftoff footage.
Russell Borogove's user avatar
5 votes
Accepted

Why do the LAGEOS' satellites have four germanium corner cube reflectors out of over 400?

D.A. Arnold "Optical and Infrared Transfer Function of the Lageos Retroreflector Array", 1978, NGR 09-015-002 (P179) confirms that they're for infrared measurements, and adds some interesting info: ...
Bob Jacobsen's user avatar
  • 12.6k
5 votes

Was Hubble really related to spy satellites?

The NASASpaceflight forum has a long discussion of the KH-11 KENNEN satellites, drawing on recently-declassified primary sources. The question was asked as far back as 1985, in Sky&Telescope ...
Hobbes's user avatar
  • 127k
5 votes
Accepted

What's the largest optical telescope mirror ever put in space?

The winner (as of 2019) would be the ESA Herschel Space Observatory with a focal mirror of 3.5M/11.5ft (Image Source) Optical could include infrared, visible and ultraviolet, but not microwaves. ...
Machavity's user avatar
  • 7,840
5 votes
Accepted

Determine envelopes for the payloads?

For STS payload induced enviroments, grab yourself a copy of the Space Shuttle User's Handbook and you will find plenty of data starting on page 31 of the pdf. Vibration, noise, thermal, pressure (...
Organic Marble's user avatar
5 votes

There are only a few suppliers of optical terminals: what is the reason?

Challenges Mass production and industrialization: The industry has geared up over decades to supply radio equipment such as phased-array antennas and hardware on satellites. Shifting the production ...
Polar_Bear's user avatar
5 votes
Accepted

How is the maximum data rate of the Psyche mission's Deep Space Optical Communications (DSOC) system expected to scale with distance?

The scaling with $1/r^4$ holds when receiving an optical signal in a way similar to a RF signal, i.e. by reading it as an amplitude signal. Photons in the IR/visible/UV range however can be detected ...
asdfex's user avatar
  • 15k
4 votes

Is there any way that real stars would move like they do in the classic Windows 3.x screensaver if traveling through space at extreme speed?

It helps to suppose that you're flying your ship somewhere closer to a galactic nucleus than we are. Sure, the nearest star to us (after the Sun) is several light years away, but if you get within a ...
hobbs's user avatar
  • 927
4 votes

When will a moon landing site be visible via telescope?

Using this page you can calculate how big a telescope must be to view any object at any distance: http://win98.altervista.org/telescopio.html Page also lists data for some known telescopes and some ...
jumpjack's user avatar
  • 3,033
4 votes

Was Hubble really related to spy satellites?

Reading Wikipedia's KH-11 Kennen I found this ... "KH-11s are believed to resemble the Hubble Space Telescope in size and shape, as the satellites were shipped in similar containers. Their ...
Jorge de la Torre's user avatar
4 votes
Accepted

How does the thin gold film in the glass of spacesuit helmets block thermal IR but transmit visible? What's the property?

@BlakeWalsh started to figure out the answer here and finished here but declined the invitation to post the answer, so I'll finish by posting it by proxy. Why is gold "gold-colored"? Several answers ...
uhoh's user avatar
  • 149k
4 votes

How does the thin gold film in the glass of spacesuit helmets block thermal IR but transmit visible? What's the property?

If I Recall Correctly, The gold (and silver) was an early version of dichroic optical filters. Thin films of gold and silver, when applied in a specific order, create "thin-film interference" which ...
Rbeal's user avatar
  • 189
4 votes
Accepted

How does the camera make the exhaust of the Electron's RP-1/LOX exhaust transparent?

In this image of a Falcon 9 takeoff (CRS-14), you can see some transparency in the exhaust of the (much larger) Merlin 1D: I can make out the rear half of the engine bells through the exhaust (this ...
Hobbes's user avatar
  • 127k
4 votes
Accepted

How would 2 JWSTs make stereo pictures?

Let's think about what stereo pictures give us scientifically rather than aesthetically. It's information about depth. How far something is away. Why scientifically? Because while bass players and ...
uhoh's user avatar
  • 149k

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