Questions tagged [observational-astronomy]

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

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2answers
656 views

Why does the background noise in this image of 2020 QG look like corduroy?

The news item Small asteroid becomes closest ever seen passing Earth: NASA contains a "handout image" with the caption: This NASA/JPL/ZTF/Caltech Optical Observatories handout image ...
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Is the rate of gravitational wave detection roughly what was expected?

LIGO's first light was back in 2002 but it has only recently started regular observation. With roughy 50 events confirmed, is it possible to compare its detection rate to predicted rates? There were ...
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What are the effects of using non-spherical lenses in refracting telescopes?

Non-spherical (or non-circular) mirrors for reflecting telescopes are common and discussed in many places... But what about elliptical, parabolic or hyperbolic lenses?
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Latitude and longitude of Eugene Shoemaker's final resting place?

Eugene Shoemaker was an esteemed and celebrated astronomer and planetary geologist. Is it possible to localize their final resting place with a latitude, longitude and feature name?
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Why isn't IMBH candidate GW190521 very “chirpy”? Which types of events will produce the most chirp-like behavior?

The first gravitational wave observations were noted for their "chirp-like" behavior; the objects would speed up as they got closer, radiating more strongly and therefore loosing energy ...
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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 ...
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1answer
52 views

Right ascension, Equinox, Positions Help

I am trying to answer the following question which I slightly understand but need a clearer explanation: What are the times of year to observe an object at X hours of RA at visual wavelength? I am ...
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1answer
46 views

what is the difference between luminosity distance and distance?

This is a very basic question but I am little confuse the difference between luminosity distance and distance. Can anyone tell me that what is the difference between luminosity distance and distance?
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Problem with making telescope

I am using a convex lens with $f=5$ cm and $5$ cm aperture, a concavo-convex lens with $f=100$ cm and $5.5$ cm aperture. I am trying to make telescope and it should have magnification of 20 x. But the ...
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1answer
83 views

Why did supernova 1987A's “String of 'Cosmic Pearls'” appear to be so lumpy 20 years later? Is it still?

NASA's A String of 'Cosmic Pearls' surrounds an exploding star is beautiful and the page says: This image shows the entire region around the supernova. The most prominent feature in the image is a ...
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How are all the intermediate images between the “lensed” and “unlensed” endpoints of this video generated?

Phys.org's ALMA sees most distant Milky Way look-alike describes the numerical image reconstruction of a strongly and very nicely lensed z = 4.2 galaxy by a by a foreground galaxy at z = 0.263 and ...
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How do they know the newly-spotted gas near the center of our galaxy is molecular without knowing what gas it is?

Phys.org's Mystery gas discovered near center of Milky Way links to Teodoro et al 2020 in Nature Cold gas in the Milky Way’s nuclear wind who's abstract is shown below. Question: My reading of the ...
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How is the roll of the Hubble telescope around its axis and the dispersive direction(s) of it's spectrometer(s) managed?

Reading Dupree et al. 2020 Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse (also in arXiv and summarized in Phys.org's Hubble finds that Betelgeuse's mysterious dimming ...
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How do magnetic fields mess with astronomers' observations?

Does anyone else watch 'Dr. Becky' on YouTube? Her March 'Night Sky News' video, subtitled 'The biggest black hole burp, a wobbly Milky Way & Betelgeuse is brighter' says that... "Dust and ...
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1answer
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What is the difference between azimuth angle and hour angle?

What is the difference between an hour angle and an azimuth angle? When I see illustrations of the two, the angles look very similar.
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How did we measure the mass of the universe?

In an wiki article, observable universe, it was mentioned that, Mass (ordinary matter) 1.5×10^53 kg I wonder how did we measure the mass of our observable universe?
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How does a cross dispersed spectrum look like in a reality (from echelle spectrographs)?

I am an analytical chemist with some interest in amateur spectroscopy. Since astronomers use echelle spectrographs to study the high resolution spectrum of the stars, someone suggested to post the ...
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Gravitational waves and gamma ray burst: how were the error bars determined for this speed of gravity calculation? Was $H_0$ used?

This newly updated answer to How precise are the observational measurements for the speed of gravity? and this answer to How is the most accurate value of 𝐺 measured? cites the November 2017 arXiv ...
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Why does Stellarium tell such imprecise distance for Betelgeuse? [duplicate]

The newest version of Stellarium, as well as the former ones, tell that Betelgeuse would be 497.95 ly plus/minus 56 ly away. Celestia also lists Betelgeuse ~500 ly away, but Celestia is comparably old....
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Has any of the orbiters or rover on Mars captured image of comet NEOWISE?

We are seeing stunning pictures of comet NEOWISE from earth (and ISS too), are there any pictures captured from Mars by an orbiter or rover, or any other spacecraft?
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75 views

How to approximate the distance at which the thin disk peaks along a given LOS from Earth for a given galactic coordinate per 1 sq deg?

The density of stars drops off exponentially from the center of the galaxy and can be approximated as follows using a cylindrical coordinate system: $$ \rho(R, z) = \rho_0 \exp \frac{-R}{h_R} \ \exp \...
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How fast is Neptune getting brighter? When was was this first noticed and reported?

This answer to Compute Planet's Apparent Visual Magnitude reports the new work on planetary magnitudes, and contains an intriguing blurb about Neptune: Neptune keeps getting brighter. No one knows ...
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Demonstration of scales for the two components (transverse and perpendicular) of Baryonic Acoustic Oscillations (BAO)

I transfer here a post that has not had any answer pn physics exchange, so I am going to delete this latter. Maybe I will have more luckiness here. In an astrophysics context about BAO (Baryonic ...
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Why in my area does NEOWISE appear so dim and small?

So, I was always amazed by images of NEOWISE around the Internet like this: Or this: Yet, all my efforts to see it or photograph it in its full glory were fruitless... 22.07.2020 22:01 Here you can ...
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How does NASA's ASTHROS stratospheric telescope compare to its James Webb space telescope?

In Space SE I've asked Would it have been cheaper and faster to put a James Webb-like Space Telescope on a balloon instead of a rocket? I linked there to a few news items: CNET: NASA to send stadium-...
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How thick are the intergalactic filaments?

Recently, in October, news came out about the faint intergalactic filaments finally being 'found'. Then, in June, astronomers announced that these things had enough normal matter in them to solve the '...
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How do astronomers detect the 'metals' in a star? If the atoms are presumably completely ionized?

Atoms and molecules usually emit their characteristic wavelengths because of the electrons' energy levels.... Do the completely ionized ('naked') nuclei absorb and/or emit EM radiation? If so, at what ...
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1answer
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Do free protons and neutrons absorb much radiation? To affect astronomers' observations? If so, at what wavelength(s)?

In a plasma, or wherever, do the completely ionized nuclei commonly absorb much EM radiation? Or any free neutrons or protons? Can astronomers detect this? Enough so that astronomers take it into ...
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Why are Delta Aquariids “for the southern hemisphere” while the Perseids are “for the north”?

In the video How to spot Comet NEOWISE, plus the largest 3D map of the Universe | Night Sky News July 20 after 05:28 Dr. Becky (Smethurst, Oxford astrophysicist) ...
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Ecliptic coordinate ranges in radians

In ecliptic coordinates, what are the ranges of ecliptic longitude and latitude in radians? Do they both go from $-\pi$ to $\pi$?
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Basic explanation of baryon acoustic oscillations; what if anything is actually oscillating?

Sci-News' Sloan Digital Sky Survey Collaboration Releases New 3D Map of Universe links to the two videos The eBOSS 3D map of the Universe SDSS releases largest 3D map of the universe ever created ...
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What observatories provide data similar to USNO?

USNO (the United States Naval Observatory) generates positions for the celestial bodies (planets, moons,stars) and provides them in the form of .bsp files and their ...
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Seeing comet NEOWISE?

Today the NY Times published an article that explained how to see NEOWISE at night. The article explains it like this: To catch NEOWISE yourself, look up at the northwest skies about an hour and a ...
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1answer
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Why didn't we see those campfires on the Sun until now?

What is it about its optics and instrumentation (aperture, sensors, filters), being in space and distance from the Sun on 30 May 2020 that allowed Solar Orbiter's HRIEUV telescope to see something ...
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Using altitude, azimuth to determine a baseline vector?

I know the equatorial coordinates of a “beam” pointing from an Earth-based observer toward some distant star. I have converted those coordinates to altazimuth coordinates for that observer and a ...
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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 ...
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1answer
73 views

Astronomical data convertion from Jy/pixel to MJy/sr?

I'm in the middle of collecting infrared data of various wavelengths. My problem is the following: SPIRE data (250µm) are in MJy/sr and PACS data (100µm) are in Jy/pixel. I would like to combine these ...
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1answer
64 views

Were radio spectroscopic observations ever used to first measure a distance successfully?

Usually, especially for an extragalactic object, its redshift is determined by optical spectroscopic redshift. But the angular resolution of early radio observations is poor and an optical counterpart ...
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1answer
42 views

Intuitive explanation for why the Doppler effect (and red-shift) happens?

I was looking for an intuitive explanation as to why the Doppler effect happens. I haven't found any, but this is what I thought: -Waves emitted travel at a constant speed -The source emits a wave -If ...
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1answer
42 views

The definition of eclipsing binary star systems

In the second minimum (the 3rd step) there is a smaller decrease in light intensity. For this to happen, wouldn't you need to be looking at the plane of orbit from above rather than directly along the ...
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1answer
53 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 ...
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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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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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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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Why are quasars so far away that they couldn't be optically resolved in the 1950's? [duplicate]

Wikipedia's Quasar includes the following in its introduction: The term quasar originated as a contraction of quasi-stellar (star-like) radio source, because quasars were first identified during the ...
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1answer
50 views

Distance between objective lens and eyepiece

I am trying to make home telescope, I have a convex lens of focal length 1000mm and eyepiece (plano-convex) with 25mm focal length. What is the ideal distance between objective and eyepiece to see ...
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1answer
53 views

Determine distance of asteroid based on two observations from different locations

Two astronomers A, B located in different regions A: 17° E, 46 ° 27 'N, B: 17° E, 22 ° 34 'S observe an asteroid at the moment it is exactly above the meridian and is in position C which is a distance ...
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48 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 ...
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1answer
94 views

Effect of black coating on the inside of a hobby telescope's tube?

I was watching this (rather old) episode of "The Making, where they show how a telescope is built in a factory. At 7:34, the cylindrical body of the telescope is shown to have a dark coating on ...

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