Questions tagged [observational-astronomy]

Questions about the techniques and practice of observing the night sky.

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What is Euclidean fluence scaling in the context of bounding constraints on FRB all-sky rates? Would non-Euclidean scaling give a different answer?

The recent Chromatic periodic activity down to 120 MHz in a Fast Radio Burst contains two paragraphs in which X's are given "assuming an Euclidean fluence scaling". To me, a non-astronomer, ...
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Can you subtract magnitude of constant source to get magnitude of variable source?

Let's say I observe a source that is actually two sources (source A and source B) where each cannot be individually resolved. Source A is a variable source and source B is a constant source. I want to ...
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Why does the 'Big Bang Nucleosynthesis' theory require that neutrinos, or at least sterile neutrinos, have a LARGE mass rather than a tiny one?

From Wikipedia, Sterile neutrino Particles that possess the quantum numbers of sterile neutrinos and masses great enough such that they do not interfere with the current theory of Big Bang ...
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What is the bright star that never seems to move and sometimes the only star in sky?

I have very little astronomy background; so apologies in advance with elementary terminology with this question. I am located in Northeast Pennsylvania and no matter what time of night 7pm, 1am, 5am ...
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How was a rock on the surface of asteroid 101955 Bennu first observed from Earth (Benben Saxum)?

Spaceref's NASA's "Tour of Asteroid Bennu" Selected for Prestigious Computer Graphics Film Festival says: It's hard to imagine what the surface of asteroid Bennu might look like - it's ...
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What was the day of the week for the total lunar eclipse (saros 61) that occurred on April 14, 32 AD?

I am interested to know if there is convincing "astronomical" evidence/data to pin down the exact day of the week for the total lunar eclipse of April 14, 32 CE. I am hoping that perhaps ...
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Could stars be seen from inside a nebula?

Nebulae look dark against the backdrop of stars, but how opaque are they likely to be from inside? In other words, if our Solar System had drifted into the middle of, say, the Horsehead Nebula, would ...
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How does the Latvian branch of LOFAR radio telescope array communicate its data without a network connection?

LOFAR technical information links to LOFAR Map from which a screenshot below shows HBA, LBA and Network options. Both the high and low band arrays are distributed in a number of clusters around Europe....
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What is use of Greek Letters in Astronomy? [closed]

We see letters such as $\epsilon$ or $\alpha$ or $\beta$ or $\eta$ etc... (possibly all Greek letters) Can Somebody state the use of all Greek letters in astronomy?
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What's known about Odd Radio Circle appearance? What would they look like if we could see them? Are they transparent/translucent in radio, or opaque?

update: March 2022: Phis.org: Astronomers reveal best image yet of mysterious odd radio circles in space Science Alert: Weird Circular Objects Observed in Space May Finally Be Explained MNRAS: ...
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What does this tweeted Astronomy Plot of the Week mean? What does it represent?

Twitter user BenneHolwerda (@BenneHolwerda) recently tweeted August 10 Astronomy Plot of the Week: And I think @SabineBellstedt and @_jessthorne summary graph deserves a spot for sure. If you work ...
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What would it take to view "the whole EM spectrum"?

I know the EM spectrum goes off both ends, but nearly everything anyone has bothered to use it for has wavelengths between $10^8$m (ELF) and $10^{-12}$m or so (gamma rays). So for the purposes of this ...
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How much time do I have left to easily spot the recently brightened Recurrent Nova RS Ophiuchi with binoculars and mild light pollution?

Excellent answers to Binocular-friendly star map to find the Recurrent Nova RS Ophiuchi? provide some helpful maps for circa 8° FOV binoculars, but due to spatial and potential meteorological ...
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Where do Astronomers usually get their wavelengths? Where do they turn to look up standard, accepted values for spectral features?

When identifying isolated observed spectral features or fitting complex observed spectra or even running complex numerical simulations, one needs a reliable, standard table of known wavelengths and ...
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Tracking deep sky objects

I have a Celestron Astromaster 130Eq. I saw all the planets in our solar system and quite satisfied. Now I am in the hunt for DSOs, but living in a city is a disaster for tracking some good-for-...
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Why would someone choose a lower resolution grating over a higher one when performing spectroscopy?

The higher spectral resolution grating would reduce the spectral range. Besides that, would a higher resolution grating reduce the signal per pixel? I thought I heard someone mentioned this to me a ...
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Using masers to measure rotational velocity of a galaxy

When measuring the rotation velocity of a galaxy, most of the times we can only directly measure radial velocity, by looking at the redshift. I read in a lecture slide that some times it is possible ...
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Radius to which all hydrogen-burning stars are known?

For the purposes of this question, I wish to consider active, hydrogen-burning stars, not deuterium-burning brown dwarfs, or stellar remnants like black holes or neutron stars. (Though including ...
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How can a 1-pixel image of a rotating asteroid be used to measure its thermal inertia?

Phys.org's Observatory in Chile takes highest-resolution measurements of asteroid surface temperatures ever obtained from earth discusses imaging of millimeter wave imaging of the surface of asteroid ...
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What is a typical "pulse rate" for a black hole "heartbeat"? Is the process better understood than it was in 2011?

The 2011 NASA Goddard video NASA | RXTE Detects 'Heartbeat' Of Smallest Black Hole Candidate mentions a heartbeat and includes a graphic of pulses from GRS 1915+105. A screenshot is shown below. No ...
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Is "magnetars don't last long — just a year to a few years" really true? Is it a misquote or perhaps taken out of context?

NASA's Two Sides of the Same Star discusses the relationship between pulsars and magnetars and contains a video also linked below. At 02:13 it quotes "Tom ...
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Proper way to average a set of color measurements?

Say we're given a set of flux measurements in two filters for a group of $n$ stars, say H-band and K-band: $F_H$ and $F_K$ From these, we can compute a color in $\Delta m$ for each of the $n$ stars, e....
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What does an electron-capture supernova leave behind? A white dwarf, a neutron star or nothing?

Somehow, none of the many articles I've read about the recent discovery of electron-capture supernovae has specifically said what they leave behind as remnants.....
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What are the oxygen or water vapor lines?

I was reading the document Recommendation ITU-R P.676-11 (09/2016); Attenuation by atmospheric gases (P Series, Radiowave propagation) in order to calculate the atmospheric losses, and there were some ...
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How is the H II 'region' directly detectable? By Compton or Thomson free-particle scattering? At what wavelengths?

The Wikipedia page on H II regions says that they are 'indirectly' detectable by the detection of doubly-ionized oxygen atoms mixed in.... (I am presuming atoms, not diatomic molecules...) But are ...
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Are plasma nuclei detectable? By the occasional emission of gamma rays, perhaps?

As stated above.... How often do nuclei stripped bare emit radiation? Can nuclei be identified by the wavelengths or amplitudes of gamma rays they emit? How about isotopes?
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Can we use asteroseismology to study neutron stars?

Asteroseismology study the propagation of sound waves inside a star to probe its internal structure. Could something similar be used to study the structure of neutron stars and put constraints on the ...
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5 votes
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Which star has the faintest absolute magnitude (largest magnitude) yet is still visible with the naked eye from Earth (either hemisphere)?

I am thinking about the Bright Star Catalogue and how it is not a good representation of a typical population of stars. The Bright Star Catalogue includes all the visible stars from Earth when viewing ...
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What is the difference between a Cassegrain telescope and a Gregorian one? Which one is better?

Of the three giant (or 'Extremely Large') new telescopes being built, the Thirty-Meter (TMT), the the Giant Magellan (GMT) and the Extremely Large Telescope (ELT), only the Magellan, from what I ...
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How can we know where a gravitational wave comes from? [duplicate]

When a gravitational wave arrives on Earth, a detector can observe tiny fluctuations of space metric. But there is no direction associated with this. Only when the second observation is made, far away ...
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4 votes
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How can a black hole merger create a black hole with an event horizon surface area larger than the sum of the two original areas?

Many popular and professional science sites said something about Stephen Hawking's black hole area theorem being proven observationally, finally, not just mathematically, to 95% confidence. For ...
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Can single black holes be observed by its lensing effect?

A comment on a question I asked left me confused. I asked about the possibility of observing a binary black hole by examining the lensing the binary produces. A binary has a different lensing effect ...
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On what basis is the information about the distance and velocity of the Voyager probes determined?

Voyager 1 was the first-ever object to reach interstellar space on August 25, 2012 when it passed beyond the sun’s realm of plasma influence (the heliosphere)[...] (source) Although some of their ...
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Is there a minimum distance between two black holes in a binary system beneath which it can't be observed as a binary?

Suppose two black holes are observable by means of their lensing effect. If these holes are orbiting around each other, then is there a minimum distance from each other to be still observable as ...
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What portion of all exo-planets can't be observed? [duplicate]

Exo-planets are usually observed by small decreases of the outgoing power of the stars accompanying them, when the planet passes between us and the star. The orbits of the exo-planets lay in one plane....
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4 votes
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Infall velocity in core-collapse supernovae

In this article Neutrino Transport in core-collapse supernovae, in the description of core-collapse supernova mechanism, it is stated that The velocity of infalling matter in the core increases as we ...
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How exactly will Trailblazer (the precursor to SatHub) help Astronomers plan their optical observations? Will it be open to the public?

Space News' Astronomers back technical efforts to reduce impacts of satellite megaconstellations while seeking regulatory solutions says: At the conclusion of the weeklong SATCON2 workshop July 16, ...
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How the data collected during 5 year DESI operation will be analyzed with regards to finding what dark energy really is?

Dark Energy Spectroscopic Instrument, or DESI at the end of it's 5 years operation will create the largest 3-D spectroscopic map of the universe. How the data collected during 5 year DESI operation ...
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Is there molecular hydrogen in the Sun's atmosphere? If so, how much, and how was that first determined and measured?

I don't have a license to practice chemistry, but I'll convert Wikipedia's bond dissociation energy of 435.7 kJ/mol to eV by dividing it by $C / N_A$ where $C$ is 1 Coulomb and $N_A$ is Avogadro's ...
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2 votes
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What is the distance between solar system and a distant galaxy

When we say a galaxy is 300 million light-years away, is that its distance now or 300 million years ago?
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Vacuum and air wavelengths in spectroscopy

In the SDSS page https://classic.sdss.org/dr7/products/spectra/vacwavelength.html, it is written Because the SDSS observes many quasars at rest-frame ultraviolet wavelengths, the data are stored in ...
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How to determine the color term for a filter with a systematically bluer offset than the standard

This is a hypothetical scenario in an attempt to test my understanding of the color term when performing photometric calibrations: Imagine we are observing stars through a B filter with an offset ...
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What are Euclidean-normalized differential source counts?

I would like to know what the Euclidean-normalized and differential source counts mean in "Euclidean-normalized differential source counts". It would be great to hear a) a clear definition ...
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6 votes
1 answer
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Conventional units for astronomical object coordinates

I would like to know what the conventional units for identifying a celestial object (J2000.0) are. For instance, I am reading a paper in which they refer to object SDSSJ170013.70+400855.6; I am ...
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2 votes
3 answers
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If a black hole was headed for our solar system and would arrive within a year, would we necessarily know of it?

Basically, is our observational technology and coverage sufficient enough to pretty much always spot incoming objects like a black hole when they're a year from arriving? If so, within what time frame ...
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Is it known in the scientific community that dark matter does not interact with light?

Does dark matter not interact with light, or does it not interact with anything in the universe? What do they talk about in the scientific community the most?
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Would we have spotted the ascent stage of Apollo 11's Eagle if it was still in orbit around the Moon?

This video: Is Apollo 11's Lunar Module Still In Orbit Around The Moon 52 Years Later? claims, based on orbital simulations, that there is a chanche that the lunar module of Apollo 11 might be still ...
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Would people on opposite sides of the earth see different details of the moon, if so are there actual photos demonstrating this?

I am aware of phases and the fact that opposite sides will see the moon flipped relative to the other but what I’m asking specifically is would the almost 8000 mile difference between the two ...
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A new (radio) neutrino telescope in Greenland?

I just stumbled upon ScienceMag news from July 14th, 2021 which says: By placing hundreds of radio antennas on the ice surface and dozens of meters below it, they hope to trap elusive particles known ...
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6 votes
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Do telescope measurements (in meters, usually) measure in a straight line, from edge to edge, or follow the curve of the mirror?

Somehow, no site or book or magazine has clarified this question for me.... Perhaps I am an idiot, but, Is the parabolic primary mirror on the new James Webb Space Telescope (JWST) 6.5 meters from ...
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