12
votes
Accepted
What are the dimensions of LIGO Detector evacuated chambers?
The arms are $4\,\mathrm{km}\,\times\, 1.2\,\mathrm{m}$:
From the LIGO webpage:
The 1.2 m diameter beam tubes were created in 19-20 m-long segments, rolled into a tube with a continuous spiral ...
- 37k
12
votes
Accepted
Was GRAVITY built to look at one star?
No, the GRAVITY instrument is multi-purpose.
This link gives you all the papers that have cited the instrument description paper. The list of papers shows that it has been used for studying: the ...
- 146k
11
votes
Which JWST instrument modes are compatible with observations of the bright trans-Earth planets Mars, Jupiter, and Saturn? Which aren't?
There are approved proposals for Cycle 1 to point the JWST at
The Jovian system
Jupiter's great red spot
Mars
Saturn and its moons and rings
In those PDFs, they describe exactly what instruments ...
- 211
10
votes
Accepted
Has Hubble photographed Venus in near IR? If so how does it compare to the new and exciting Parker Solar Probe image?
This web page -- "Here is why the Hubble Space Telescope only looked a few times at Venus (and why it looked at the Moon instead)" -- seems like a pretty good answer to your main question (...
- 16.4k
10
votes
Accepted
Is there a limit to the distance of detectable gravitational wave events?
Several factors influence whether a source of gravitational waves at a certain distance is observable by a certain instrument. One way to compute the limit to the distance is explained in Abadie et al ...
- 425
9
votes
Accepted
Did they ever figure out why Parker's WISPR cameras were able to see the surface of Venus? Mischaracterized filter, or unexpected atmospheric window?
There's actually a paper by Wood et al. (2022) that came out focused on this. It discusses the expected detection given the expected emission (using a model that combines the surface emission and the ...
- 16.4k
8
votes
Accepted
How could a 20 inch space telescope "be able to make out Earth-size planets" orbiting Alpha Centauri?
I'm not familiar with the design of the ProjectBlue telescope, but I think you have answered your own question.
The habitable zones for Alpha Cen A and B, are approximately centred at 1.25au and 0....
- 146k
7
votes
What would a kHz gravitational wave detector look like? (mountains on millisecond magnetars) How would it differ from LIGO/Virgo?
In principle, not much different to LIGO, since LIGO is sensitive to kHz gravitational waves. But you need to find ways to increase the sensitivity at kHz frequencies, without compromising response at ...
- 146k
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 ...
- 2,319
7
votes
Which JWST instrument modes are compatible with observations of the bright trans-Earth planets Mars, Jupiter, and Saturn? Which aren't?
All modes can be used. But for bright targets, observations are limited to specific filters, subarrays, regions of the target planet, or spectral intervals.
James Norwood and colleagues wrote a paper ...
- 2,039
6
votes
Accepted
What is the detection threshold of gravitational waves for LIGO?
I'm afraid this is not straightforward
The amplitude of the gravitational wave strain signal from a merging compact binary (neutron star or black hole) is
$$h \sim 10^{-22} \left(\frac{M}{2.8M_{\odot}}...
- 146k
6
votes
Accepted
How exactly did JWST take a "selfie" of its own primary mirror, and what is the real purpose of this capability?
Let us just ask Lee Feinberg, the Webb Optical Telescope Element Manager:
How exactly did JWST take a "selfie" of its own primary mirror?
In this video at 2:09:
There's actually a special ...
- 2,879
6
votes
At the intersection of engineering and astronomy in its structure as a scientific discipline
Yes, there is an intersection between astronomy and engineering. In my experience, it will mostly be astronomers who have a flair for technology and instrumentation who at some point, either from the ...
- 37k
5
votes
How can Mercury's sodium tail be imaged?
Yes, it is possible; see https://twitter.com/sevospace/status/1328082050889490433
However, M. Voltmer used a “custom-made sodium filter,” without giving any details…
- 6,701
5
votes
Accepted
How does ALMA produce stable, mutually coherent ~THz local oscillators for all of their dishes?
ALMA produces stable, mutually coherent ~THz LO (Local Oscillators) for all the antennas by...
Using a single central LO and piping it to every antenna via fiberoptic cable! The fiber expands and ...
- 16.2k
5
votes
How do astronomical spectrometers measure spectra from single stars separately, without contamination from all of the nearby stars?
I imagine it's done differently based on the goals. Anything wanting to study just one object could simply mask out everything else. But the Sloan Digital Sky Survey studies numerous objects at once....
- 5,562
5
votes
Accepted
Is "monochromatic source" different than "monochromator" in astronomical instrumentation?
Is "monochromatic source" different than "monochromator" in astronomical instrumentation?
Sure!
"Monochromatic source" is a very general term for any source of radiation ...
- 31.4k
4
votes
How to calculate luminosity in g-band from absolute AB magnitude and luminosity distance?
Here is my attempt to reconcile your calculations.
If the AB g-band apparent magnitude is 22.5, then the flux density in the g-band is given by
$$f_{\nu} = 10^{(-48.6-22.5)/2.5} = 3.63 \times 10^{-29}...
- 146k
4
votes
What is the detection threshold of gravitational waves for LIGO?
Figure 1 of this paper shows the horizon distance (distance to which a circularly polarised overhead signal would be detected at SNR 8) for larger mass systems up to total mass of 1000 solar masses, ...
- 591
4
votes
Is there a limit to the distance of detectable gravitational wave events?
As an addendum to Sexti Empirici answer note that LIGO and Virgo have not yet reached their full "design" sensitivity. Each run their sensitivity is further improved. The current observation run (O3) ...
- 2,511
4
votes
Number of lenslets in wavefront sensor array
Generally speaking as many as possible because the number of lenslets determines the lateral wavefront resolution. But in reality there are a few factors to be considered.
Wavefront sensor
Say your ...
- 454
4
votes
What leads an observer to choose a narrow slit over a wide one (and vice-versa) when observing?
You seem to have all the ingredients apart from the variables of what size your detector pixels are (either physically or binned in software/hardware) and the angular extent of the object you are ...
- 146k
4
votes
Why (the heck) is the basic angle of GAIA 106.5°?
I did not find anything conclusive on the web, and I am yet waiting to receive feedback from ESA's contact page. In a German speaking IT forum there is something a bit less vague than the FAQ cited in ...
- 5,526
4
votes
Is the difference between LIGO & Virgo and their "Advanced" versions really generational, or were these just planned incremental upgrades?
I think this is largely a matter of what you decide is incremental as opposed to a generational change.
The basic location and overall size and detection principle of the interferometers did not ...
- 146k
4
votes
Accepted
What would a kHz gravitational wave detector look like? (mountains on millisecond magnetars) How would it differ from LIGO/Virgo?
To briefly supplement Rob's answer, there is at least one concept being floated for a gravitational-wave detector which is explicitly targeting kilohertz gravitational waves and sacrificing ...
- 76
4
votes
Accepted
Do circa 1 THz radio telescope front end amplifiers actually down convert before amplifying? At what frequency does amplification become untenable?
An article in Astronomy & Astrophysics 1 (A. M. Baryshev et al., A&A 577, A129 (2015)) titled “The ALMA Band 9 receiver
Design, construction, characterization, first light” covers this.
The ...
- 596
3
votes
Is the difference between LIGO & Virgo and their "Advanced" versions really generational, or were these just planned incremental upgrades?
I don't feel that ProfRob's answer does the step to advanced LIGO justice.
First, it is important to recognize that LIGO, from its inception, was envisioned as a two-stage project. From Caltech`s ...
- 2,511
3
votes
How can Mercury's sodium tail be imaged?
It can, and it has been imaged by ground-based photography. Carl Schmidt dedicated his PhD thesis to Mercury and in particular its sodium tail. Therein he describes the setup and procedure.
The - to ...
- 17.5k
3
votes
What is an "Off Rowland-circle Telescope"? Are there "On Rowland-circle Telescope" as well?
The term 'off-Rowland-circle telescope' is a bit awkward, I think normally we would call the arrangement of FORTIS an off-Rowland-circle spectrograph, and they probably just used the word 'telescope' ...
- 1,084
3
votes
Accepted
What is the large astronomical instrument shown in this 1918 eclipse expedition photo?
This construct was a telescope. Citing this article:
Owing to the difficulty of erecting a double tower, most other astronomers follow the mechanically simpler plan of laying the camera tube ...
- 15k
Only top scored, non community-wiki answers of a minimum length are eligible