Questions tagged [observational-astronomy]

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

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18
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2answers
1k 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 ...
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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 ...
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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 ...
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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 ...
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1answer
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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 ...
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1answer
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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 ...
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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 ...
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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 ...
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1answer
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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 ...
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1answer
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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 ...
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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 ...
18
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1answer
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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 ...
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1answer
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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 ...
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1answer
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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 ...
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1answer
632 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 ...
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1answer
123 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 ...
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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 ...
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4answers
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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?
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1answer
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Will 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". NPR's Joe ...
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2answers
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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 ...
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7answers
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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 ...
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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 ...
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1answer
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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 ...
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2answers
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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.
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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 ...
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1answer
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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? ...
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1answer
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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 ...
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1answer
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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 ...
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1answer
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How can we tell the difference between matter and antimatter by observation in space?

I just was wondering and searching on the internet with little luck in the topic. On Antimatter Wiki they tell the observable universe is built up by matter. I read antimatter can be detected in ...
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1answer
228 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 ...
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1answer
432 views

Have there been studies of "old photons" to see just how constant things like Planck constant has been?

The question Are photons aged? and answers therein have got me thinking: I vaguely remember hearing something about experiments where "old photons" were collected by large telescopes from very ...
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1answer
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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 ...
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1answer
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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 ...
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1answer
681 views

Building a floating, ocean-going giant radio telescope?

Given the loss of the Arecibo telescope: Is anybody aware of any efforts or studies towards a floating, ocean-going radio telescope of with 500m diameter or more? The idea is floating (pun intended) ...
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1answer
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Will Gaia detect inactive neutron stars?

Will the astrometric precision of the Gaia space telescope be able to detect the gravitational influence of cold old solitary neutron stars on the movements of stars? At least in a statistical sense ...
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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 ...
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1answer
230 views

Might the SpaceX Roadster intercept any ongoing surveys?

There are star survey telescopes in space, and on Earth. I don't really know how to begin to know where they will all be looking for the next few months. On the off-chance that someone does, or can ...
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2answers
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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 ...
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1answer
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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 ...
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Has radio astronomy ever been done on objects that appear very close to the Moon? Is this avoided?

This answer to Which kinds of astronomical observations most need to avoid the Moon being up? mentions For completeness - radio, mid-infrared and mm-wave observations are unaffected (unless the ...
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1answer
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How far away is the nearest compact star remnant likely to be?

Neutron stars and black holes are hard to detect when they are solitary, and there seems to be big uncertainties about how common they are. White dwarfs are much easier to detect and the nearest one ...
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Why haven't I seen the Moon?

It has been some time since I've seen the Moon. What are the conditions that might affect whether or not the Moon is visible within a 24-hour period? Please take into consideration any notable ...
8
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1answer
280 views

Does this amateur observation hold a record even including robotic searches for supernovae?

The new paper in Nature A surge of light at the birth of a supernova (doi:10.1038/nature25151) describes the fortuitous capture of a supernova "Shock Breakout" - the earliest rise in brightness of a ...
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3answers
961 views

Why do stars twinkle but planets don't [duplicate]

Many people say that stars twinkle because of Earth's atmosphere. However, the atmosphere is still there when we look at planets and don't see they twinkling. Is there a clear scientific consensual ...
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1answer
286 views

How big will Apophis appear?

How big will Apophis appear in the sky at its closest point of approach in 2029? Will it compare to the moon? How long will it linger as it passes?
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How can Mercury's sodium tail be imaged?

I recently learned that Mercury has a sodium tail. Can this sodium tail be imaged with a ground based telescope? Is so, what is the minimum setup required to be able to take a picture of it? Do you ...
5
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2answers
102 views

What's still needed before we can observe orbits of exomoons thereby weighing exoplanets?

Comments below this answer to How do we weigh a planet? point out that we currently cannot (or at least have not) detect moons around exoplanets, much less measure the sizes and periods of their ...
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1answer
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How do OGLE-III and GAIA measure the mass of free microlensing black holes?

What is the "hypothesized lower mass gap" between 2.5 and 5 solar masses? eventually links to Constraining the masses of microlensing black holes and the mass gap with Gaia DR2. The angle of ...
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2answers
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Observation of Gravitional waves by LIGO from binary black hole merger

I read the paper "Observation of Gravitational Waves from a Binary Black Hole Merger" https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.116.061102 I tried to understand all the graphs ...
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1answer
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What would "the next GAIA"-like instrument be like? Could it simply be a 3 to 5x scaled-up version of the same beautiful system?

This excellent, thorough and well-sourced answer to Has a gravitational microlensing event ever been predicted? If so, has it been observed? mentions several works where hundreds to thousands of ...

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