Questions tagged [observational-astronomy]

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

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67
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4answers
9k views

How does the Earth move in the sky as seen from the Moon?

I just want to be sure I am visualizing this correctly, because it seems odd. The Moon is tidally locked to the Earth but there are wobbles to its motion due to libration. So from a point on the ...
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6answers
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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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3answers
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If Earth is tilted, why is Polaris always above the same spot?

Why is Polaris, the North Star, always above (or near) the North Pole? If Earth is tilted, Polaris' path should be in winter 23 degrees away from its path in summer, or not?
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2answers
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How was the mass of Venus determined?

The mass of Venus seems rather complicated to determine to me: Venus doesn't have any satellites, so you can't just apply Kepler's third law (like you would with Jupiter or Saturn for instance) to ...
35
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3answers
656 views

If you lived on the far side of the Moon, how could you infer the existence of Earth?

Suppose that you deposit an astronomer, armed with our current knowledge of orbital mechanics, on a dome on the far side of the Moon, so that the Earth is perpetually hidden from them. (And, of ...
29
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1answer
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How is it possible that we haven't discovered anything in the Oort cloud yet?

The Oort cloud is a hypothetical cloud of small icy bodies surrounding the Sun at more than 1000 AU. It is thought to be a vast reservoir of comets that occasionally get disrupted, sending comets ...
29
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1answer
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Why is there a gap in this image of supernova discoveries?

I came across this gif showing supernova discoveries from the late 19th century to 2010. Here's the data in 2010: Notice that there's a prominent region shaped like an inverted U in which there are ...
28
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2answers
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Which of the planets would be detected if they were exoplanets?

An (almost-)omnipotent being selects the solar system, presses Ctrl+C, and then Ctrl+V several times, creating copies at distances of 5, 500, 50.000, and 5.000.000 light-years away. All in a direction ...
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3answers
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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 ...
25
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4answers
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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 ...
24
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8answers
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Why can't we see distant galaxies with the naked eye?

If light keeps travelling in a straight line, why can't we see distant galaxies with the naked eye? Surely if you stared long enough, the light from them would eventually hit your eye? I apologize if ...
22
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6answers
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Puzzling quotes from astronauts about earth size

I have no doubt that we have been to the moon. This question has nothing to do with a moon landing hoax. But, there are two quotes from two different astronauts regarding the size of the earth as ...
21
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5answers
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How was Trappist-1 discovered?

I was going through all the questions in this community related to TRAPPIST-1 in order to know how planets TRAPPIST-1b to TRAPPIST-1h were discovered, but there aren't any. How were they discovered?
21
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2answers
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At what distance from Earth would our Sun be the same apparent magnitude as the next brightest star in the sky?

When I stand outside looking at the night sky, to my untrained eye, everything except the moon looks like a star. I know intellectually that some are planets circling our sun, and some are entire ...
21
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1answer
396 views

How often do comets survive passage by the Sun?

I had heard that comet ISON might not survive a close pass by our Sun, and I was curious about the odds of how other comets had fared. So, how often do other comets survive a close pass by our sun? ...
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2answers
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Why are wavelengths shorter than visible light neglected by new telescopes?

The diagram below, which I stole from this post by @HDE226868, shows that angular resolution as a function of wavelength suddenly drops by three orders of magnitudes from visible to UV-light. The ...
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2answers
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When was the martian dichotomy first observed?

The North and South hemispheres of Mars are very different one from another. They have different elevations, different crust thickness, different surface ages. This is known as the martian dichotomy. ...
18
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2answers
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Why does the Fourier transform of this CMB image have a hole in it?

The BBC's Desert telescope takes aim at ageing our Universe contains the image below of the Cosmic Microwave Background from the Atacama Cosmology Telescope or ACT. It looks like this is plotted with ...
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 ...
17
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1answer
412 views

Have we ever observed a body, such as a large asteroid, “hitting” the Sun?

Some other SE questions about launching ICBM's into the sun got me wondering whether we have ever observed an object on a path that intersected with the Sun? How close did it get?
17
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2answers
592 views

How long should it take for us to observationally determine if Caltech's Planet Nine is really there?

Caltech just released a report that says there is possibly a large (10 earth mass) planet in a remote orbit (10 - 20 thousand year) that explains a lot of observations of Kuiper Belt objects. How long ...
17
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4answers
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How Would a Neutron Star Actually Appear?

Having seen many pictures produced by artists of neutron stars and planets that orbit some of them, I was wondering how a pulsar would appear to a human being, in visible light (assuming the intense ...
17
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1answer
240 views

How can an amateur astronomer verify the position of near Earth objects?

Sometimes, hobby-astronomers use rather professional means to observe the big voids of space. Every now and then (think in months, not days) even I can locate an NEO (near Earth object). Now, I'm ...
16
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3answers
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What is the probability of seeing a neutron star as a pulsar?

Pulsars are neutron stars that emit a beam of electromagnetic radiation that is not aligned with its rotation axis. If the Earth passes through that beam of radiation, we see a pulsar. Pulsars are ...
16
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1answer
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The newly discovered comet NEOWISE has been given the name C/2020 F3. What is the meaning of the F3 and the C in this name?

The new comet C/2020 F3 was first spotted by NASA's NEOWISE satellite in March 2020. It is now visible in the NE sky just before dawn. The C may refer to it's non-periodic nature (so far). What does ...
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2answers
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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 ...
16
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2answers
442 views

Did nobody in the Astronomy community think 12,000 new satellites in LEO might be a problem?

This answer to Can / should the Starlink satellites be blackened? mentions Space News' SpaceX working on fix for Starlink satellites so they don’t disrupt astronomy where SpaceX chief operating ...
16
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2answers
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How do satellites impede current telescopes?

As we send up more and more satellites, it stands to reason that our view of the universe becomes more and more obscured. I would certainly expect for example that a large telescope such as the LSST ...
16
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1answer
608 views

How do I build a stargazing aficionado's Sun funnel to observe our nearest star safely?

How do I observe the Sun safely, with tools I could build myself and without breaking the bank? If I wanted to build a Sun funnel on my own and use it on my enthusiast grade telescope, how would I do ...
16
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1answer
922 views

What is the object in this photo?

What object is in this photo? View coordinates: $47.25103 \ \ 38.81697$ Time: $2013$-$11$-$23 ~21$:$00 +4 ~UTC$ Sony $A580, \ 50mm f/1.4 15"$
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8answers
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Has great eyesight been necessary for astronomers?

In a different (but somewhat related) field, some baseball stars have been known to have "baseball eyes." That is, an exceptional ability to visually follow the trajectory of a 90+ mph baseball to a ...
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2answers
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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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6answers
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How “fast” do astronomical events occur?

I've seen quite a few news about astronomy but I'm not deep into knowing how it works or how people observe it. It got me thinking: if I want to watch a supernova for example, how long will I have to ...
15
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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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4answers
595 views

How would I measure that I'm at a pole?

How would a person measure that he is at a planetary pole? My first inclination is to use a sextant to ensure that the Sun remains at a constant inclination. However, due to the orbit around the Sun ...
15
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3answers
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What wavelength to best detect the “9th planet”?

We know that the reflected sunlight will make detecting the 9th planet very difficult in the visible light. Is there another band that will be more likely to detect it? What is the surface temperature ...
15
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2answers
971 views

Are there neutron stars whose magnetic axis and rotating axis are the same, and if so what will happen?

I know that there's probably a higher chance of having a neutron star that has its magnetic axis inclined to the rotational axis rather than having it perfectly aligned. If they are not aligned, the ...
15
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2answers
618 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 ...
15
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1answer
2k 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 ...
15
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1answer
573 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 ...
14
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3answers
2k views

How can I safely observe a Solar Flare?

Solar Flares obviously release extreme amounts of energy and extend thousands of miles out into space. Because they are so big I would like to be able to observe some of these events through a ...
14
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1answer
715 views

How is the Hubble constant determined from gravitational waves?

We know there is a discrepancy between measurements of the Hubble constant, $H_0$. On one side there is the method of the Planck mission, where they use the CMB and the $\Lambda$CDM model to determine ...
14
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1answer
996 views

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 ...
14
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2answers
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How does angular resolution of a telescope translate to its parallax precision?

We can often read in the scientific and also more casual reader literature and articles about the angular resolution of various telescopes and other optical equipment, be it ground based or onboard ...
14
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2answers
354 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 ...
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1answer
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How can the Sun block an X-ray telescope from observing a QPO galaxy “for several years”?

Phys.org's Black hole's heart still beating says: X-ray satellite observations spotted the repeated beat after its signal had been blocked by our Sun for a number of years. and links to the Open ...
13
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1answer
953 views

How is an exoplanet characterised as “Earth-Like”?

Which features or characteristics are taken into account to characterize an exoplanet as "Earth-Like"?
13
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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 ...
12
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1answer
142 views

Is it possible to observe if there is traces of life on an exoplanet?

We can observe exoplanets, but is it possible with today's technology to observe if there is life as we know it on an exoplanet? What do you look for when doing this kind of observation?
12
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1answer
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How would astronomical seeing on Mars differ from that on Earth?

Astronomical seeing is the limiting factor for the resolution of all but the smallest Earthbound telescopes. Source Stunning advances in adaptive optics (along with it's predecessor speckle ...

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