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Questions tagged [observational-astronomy]

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

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21 votes
2 answers
2k views

Are there any galaxies which fell out of sight horizon due to cosmic expansion?

If farthest galaxies run away from us with acceleration making them exceed speed of light, we should expect them to disappear from sky among time with increasing quantity. Did we observe this? Can we ...
Waldemar Gałęzinowski's user avatar
62 votes
6 answers
8k views

Why hasn't the "9th Planet" been detected already?

In the comments to this question, there was considerable doubt placed as to the subject of if the so called "9th planet" really exists. That wasn't really the intent of the previous question, so I ask ...
PearsonArtPhoto's user avatar
12 votes
2 answers
898 views

Why aren't ground-based observatories using adaptive optics for visible wavelengths (circa 2016)?

Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing. The atmospheric effects are quite ...
uhoh's user avatar
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16 votes
2 answers
2k views

What will it finally take to accurately measure the distance to Betelgeuse?

Comments below What is the maximum distance measurable with parallax? discuss challenges associated with parallax measurements of Betelgeuse and link to Wikipedia’s Betelgeuse; Distance measurements ...
uhoh's user avatar
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37 votes
3 answers
2k views

If Alpha Centauri A's solar system exactly mirrored our own, what would we be able to detect?

Suppose there was an exact replica of our solar system 4.4 ly away (people included). What would we be able to detect and with what telescope(s)? Which planets? Could we detect radio transmissions and/...
Nick T's user avatar
  • 471
11 votes
1 answer
2k views

Why the blank wedges in this very early 21 cm map of the Milky Way? (Oort et al. 1958)

Jan Oort was a pioneer in radio astronomy. Wikipedia says: It has been written that “Oort was probably the first astronomer to realize the importance” of radio astronomy. “In the days before radio ...
uhoh's user avatar
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3 votes
1 answer
185 views

What is the physical geometry of this apparent "eclipse" of a tiny moon of Asteroid Florence?

Below is a small GIF made from a small subset of images contained in the original 36MB GIF found at https://cneos.jpl.nasa.gov/images/news/florence.p5us.1Hz.s382.sep01.gif as I just found in the Sky ...
uhoh's user avatar
  • 30.6k
2 votes
1 answer
261 views

Will the Magdalena Ridge Optical Interferometer be able to image extended objects like the surface of the Moon?

Inspired by several questions: When will a moon landing site be visible via telescope? Could the E.H.T. produce an image of the human artifacts on the moon? Picture of equipment left on the Moon? ...
uhoh's user avatar
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10 votes
1 answer
1k views

How (the heck) was this photo of Venus at inferior conjunction (between us and the Sun) taken?

This great answer by @gerrit discussing planetary phases seen in visible light contains the image I've included below. According to the Wikimedia Commons link these are ESO images from the Venus ...
uhoh's user avatar
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3 votes
1 answer
256 views

Has optical interferometry been done at radio frequency using heterodyning with a laser in a nonlinear material?

If one collects narrow band optical emission from a large telescope with frequency $f_1$ and mixes it in a nonlinear crystal with laser light of a nearby frequency $f_2$, it would produce two new ...
uhoh's user avatar
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2 votes
1 answer
549 views

How did single dish (or single receiver) radio telescopes originally generate images?

That actually sums up my question nicely: How did single dish (or single receiver) radio telescopes originally generate images? - or at least 2D intensity maps or contour plots. Early radio ...
uhoh's user avatar
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21 votes
2 answers
1k views

How will Starlink affect observational astronomy?

I have recently found that people around the world have been posting observations of a line of moving objects in the sky which is very likely to be a part of Starlink satellite constellation, such ...
Leo Liu's user avatar
  • 381
15 votes
1 answer
2k views

What is it exactly about these flares of infrared light from Sgr A* that "confirms" it is a supermassive black hole?

CNET.com's SCI-TECH Scientists confirm a 'supermassive black hole' at the heart of our galaxy It's "mind-boggling", they say. This links to Astronomy.com's Scientists finally confirm the Milky Way ...
uhoh's user avatar
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14 votes
1 answer
2k views

Are astronomers waiting to see something in an image from a gravitational lens that they've already seen in an adjacent image?

@RobJeffries' answer to the question Does gravitational lensing provide time evolution information? points out that there can be a substantial different in arrival times of light from a given source ...
uhoh's user avatar
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10 votes
4 answers
1k views

How are rogue planets discovered?

Planets are usually found by observing a star and waiting for the light level to drop when a planet passes in front of it, but what about rogue planets that don't have host stars?
Michael Blake's user avatar
6 votes
1 answer
331 views

What causes "North-South ambiguity" when doppler radar imaging a planet surface equator?

I'm having a hard time understanding why there would be this ambiguity. Also, why would this be not the case if the planet was viewed pole on? Edit: "North South ambiguity" is a term used in ...
MinYoung Kim's user avatar
4 votes
1 answer
327 views

Will the first Event Horizon Telescope image of the Milky Way's black hole Sgr A* just be another lumpy orange donut?

@HDE226868's answer to Why doesn't the black hole in the center of the Milky Way glow similarly to the famous M87 image? explains that neither black hole is orange and any Event Horizon Telescope ...
uhoh's user avatar
  • 30.6k
4 votes
1 answer
315 views

What equipment and techniques were used to study Betelgeuse's diameter in 1920?

Comments below What is the maximum distance measurable with parallax? discuss challenges associated with parallax measurements of Betelgeuse and link to Wikipedia’s Betelgeuse; Distance measurements ...
uhoh's user avatar
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4 votes
1 answer
188 views

What can be learned from low frequency radio astronomy available outside of Earth's ionosphere?

As discussions and answers to How large does refraction become in radioastronomy? point out, it is difficult to do radio astronomy much below 30 MHz (or 10 MHz depending on how aggressive you are in ...
uhoh's user avatar
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3 votes
0 answers
178 views

What does "GPU-accelerated butterfly matched filtering over dense bank of time-symmetric chirp-like templates" mean? (GW170817)

A new analysis of gravitational wave (and other data) from GW170817 on 2017-Aug-17 has been published, strongly suggesting that the merger of two neutron stars resulted in a large, rapidly rotating ...
uhoh's user avatar
  • 30.6k
2 votes
1 answer
220 views

Why did it take five years to "figure out" how to use astrometric calibration sources to deblur LOFAR images?

Quanta Magazine's The Hidden Magnetic Universe Begins to Come Into View is a fascinating review of a rapidly evolving field in astronomy. It contains some statements: In their paper last year, van ...
uhoh's user avatar
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25 votes
4 answers
4k views

Are there any double stars that I can actually see orbit each other?

If I had a nice amateur telescope†, are there any multiple star systems that I could observe over a few years or a few decades and actually see the movement of one or both of them over time? My short ...
uhoh's user avatar
  • 30.6k
17 votes
1 answer
3k views

Has Hawking Radiation Ever Been Observed?

I know Hawking Radiation has firm theoretical footing, but has a signal ever actually been observed? What observational research is being done to attempt to see this effect? Is it simply too tall an ...
astromax's user avatar
  • 5,953
17 votes
1 answer
1k views

Will the Vera C. Rubin Observatory (formerly the LSST) make a significant increase in the rate of astronomical event alerts?

The NPR news article and podcast New Telescope Promises To Revolutionize Astronomy updates the status of the "Large Synoptic Survey Telescope under construction on Cerro Pachón in Chile". ...
uhoh's user avatar
  • 30.6k
13 votes
1 answer
823 views

If I can't unscramble an egg, how do Astronomers unscramble views gravitationally lensed by complex mass distributions?

Quanta Magazine's Two Weeks In, the Webb Space Telescope Is Reshaping Astronomy highlights two submissions to arXiv soon after the first images were released: "Three days later, just minutes ...
uhoh's user avatar
  • 30.6k
10 votes
1 answer
420 views

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

The New Horizons spacecraft is almost 50 AU from Earth and near-simultaneous images taken by its telescope and one on Earth have demonstrated parallax without relying on the movement of Earth in it's ...
uhoh's user avatar
  • 30.6k
7 votes
1 answer
297 views

Is 486958 Arrokoth (2014 MU69 aka Ultima Thule) the only solar-system object determined to be binary by occultation?

The asteroid 486958 Arrokoth was discovered to be binary by astronomers lugging a bunch of telescopes around (I think) camping with them. The timing offered additional astrometry for the orbit ...
uhoh's user avatar
  • 30.6k
6 votes
1 answer
418 views

How did VLT's adaptive optics obtain this resolution for Neptune? Is it really working in visible wavelengths?

This image of Neptune taken with the VLT is really impressive. The resolution is achieved by recent improvements in the adaptive optics. Gizmodo: New Super-Crisp Images of Neptune Show How Far Our ...
uhoh's user avatar
  • 30.6k
5 votes
1 answer
376 views

Is there a standardized "Astronomical Alert" system?

“Who saw” the binary neutron star merger first? What was the sequence of events? (GRB/GW170817) highlights a particularly notable astronomical alert, but I am sure that there are alerts triggered by ...
uhoh's user avatar
  • 30.6k
3 votes
1 answer
1k views

Which techniques are used to convert radio signals received by antenna to images?

I realized that after answering the question How do astronomers convert radio signals received by their antenna to images? I had missed the point that the OP was only asking about software. I've ...
uhoh's user avatar
  • 30.6k
3 votes
1 answer
186 views

Has a gravitational microlensing event ever been predicted? If so, has it been observed?

This answer to Are astronomers waiting to see something in an image from a gravitational lens that they've already seen in an adjacent image? describes "Deja vu all over again" (SN "...
uhoh's user avatar
  • 30.6k
3 votes
2 answers
238 views

When would we detect a tiny meter size natural satellite in a geostationary orbits?

A natural, tiny (meters-size, maybe 10.000kg mass) natural satellite could be trapped in a geostationary orbit. I wondered for quite some time: When and how are we able to detect these satellites? I ...
Mario Krenn's user avatar
53 votes
4 answers
7k views

Is there any role today that would justify building a large single dish radio telescope to replace Arecibo?

It seems that most of the modern radio astronomy instruments and observations that make the news are interferometers or phased array systems of one kind of another. Is there any application left for ...
Steve Linton's user avatar
  • 10.3k
31 votes
3 answers
4k views

Why can't we observe the Oort cloud with a telescope?

The Oort cloud is a hypothetical structure based on our observation of long-period comets. There are currently proposals to design probes to confirm the existence of the Oort cloud. Now, sending a ...
called2voyage's user avatar
  • 6,290
18 votes
1 answer
4k views

Why does the moon sometimes appear giant and a orange red color near the horizon?

I've read various ideas about why the moon looks larger on the horizon. The most reasonable one in my opinion is that it is due to how our brain calculates (perceives) distance, with objects high ...
Larian LeQuella's user avatar
16 votes
1 answer
724 views

What are the current observational limits on the existence of Dyson spheres/swarms/rings?

A Dyson sphere/swarm/ring is a hypothetical structure an extra-terrestrial entity would construct to collect a large fraction of its host star's light, and would likely generate a fairly strong ...
Guillochon's user avatar
  • 1,582
15 votes
2 answers
553 views

What percent of planets are in the position that they could be viewed edge-on from Earth? (and thus able to undergo transits)

Star number 12644769 from the Kepler Input Catalog was identified as an eclipsing binary with a 41-day period, from the detection of its mutual eclipses (9). Eclipses occur because the orbital ...
Larian LeQuella's user avatar
11 votes
2 answers
3k views

Why moon sighted only in Kerala but not in rest of India?

I know for most of you the question may look silly, but Kerala is a state in India where the moon (Ramadan moon) will be sighted but not in rest of India. I was reading the news article where I got a ...
goodyzain's user avatar
  • 213
11 votes
2 answers
1k views

How was Earth's "quasi-satellite" 2016 HO3 "first spotted" and it's orbit determined?

Under a question I asked a few days ago Have there been any documented mini-moons since 2006 RH120? @Hobbes mentioned the recent news about 2016 HO3 - a near-Earth asteroid that stays near Earth ...
uhoh's user avatar
  • 30.6k
7 votes
7 answers
1k views

Radio telescope targeting

How do you target a radio telescope on the precise object you wish to observe? You can point it in the general direction but how do you get the information from the exact point in the sky that you are ...
Nigel J's user avatar
  • 71
6 votes
2 answers
128 views

After only one eclipse of its X-ray bright primary, how can astronomers estimate the first extragalactic exoplanet's period to be about 70 years?

Phys.org's Astronomers may have discovered the first planet outside of our galaxy links to Di Stefano et al. 2021 A possible planet candidate in an external galaxy detected through X-ray transit (...
uhoh's user avatar
  • 30.6k
5 votes
1 answer
566 views

How bright is the Crab Pulsar's 30 Hz modulation in visible light? What color is it?

This answer to Has great eyesight been necessary for astronomers? mentions Astronomer Jocelyn Bell Burnell's recounting of a likely first visual observation of a pulsar. This can be found for example ...
uhoh's user avatar
  • 30.6k
4 votes
2 answers
325 views

Sunset on [Mountain] from [Viewing Point]

How do I get the days in this year when the sun will set exactly on top of Fuji as viewed from Enoshima. I shamefully admit that I just want to take a nice picture of Fuji.
Caesar's user avatar
  • 193
4 votes
0 answers
135 views

How did Michelson measure the diameters of jupiter's moons using optical interferometry?

In Betelgeuse: How its Diameter was measured (Chant, C. A., Journal of the Royal Astronomical Society of Canada, Vol. 15, p.133, Bibliographic Code: 1921JRASC..15..133C) the author says: The paper in ...
uhoh's user avatar
  • 30.6k
4 votes
2 answers
278 views

What would a kHz gravitational wave detector look like? (mountains on millisecond magnetars) How would it differ from LIGO/Virgo?

The abstract of Gravitational waves from mountains in newly born millisecond magnetars says: In this paper we study the spin-evolution and gravitational-wave luminosity of a newly born millisecond ...
uhoh's user avatar
  • 30.6k
3 votes
2 answers
348 views

Is the difference between LIGO & Virgo and their "Advanced" versions really generational, or were these just planned incremental upgrades?

I just learned the term "third generation gravitational wave detector" in answers to What would a kHz gravitational wave detector look like? (mountains on millisecond magnetars) How would it ...
uhoh's user avatar
  • 30.6k
2 votes
2 answers
269 views

What is the LSST now? Where does LSST end and Vera C. Rubin Observatory begin?

Space.com's It's Official: Vera Rubin Observatory Named to Honor Dark Matter Scientist says: "We're here today to focus on the major renaming of the facility after a pioneering astronomer, that ...
uhoh's user avatar
  • 30.6k
1 vote
1 answer
379 views

How do ASKAP's focal plane phased array feeds interact with the entire array phasing?

Sky & Telescope's ASKAP Joins the Hunt for Mysterious Bursts says: A new telescope, the Australian Square Kilometre Array Pathfinder (ASKAP), has joined the search for energetic and elusive fast ...
uhoh's user avatar
  • 30.6k
1 vote
1 answer
231 views

In the 1950's how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)?

In my question Why are quasars so far away that they couldn't be optically resolved in the 1950's? I included the following short paragraph, but then added strikethrough to the second sentence ...
uhoh's user avatar
  • 30.6k
1 vote
1 answer
230 views

How did I flip some mirrors around in the dark at 3 AM and change the focal length of a 24 inch Boller and Chivens?

Current answer(s) to How do telescopes "zoom" and change angle of view? are "they don't", but traditional large genera-purpose observatory telescopes do sometimes (often?) have ...
uhoh's user avatar
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