# Questions tagged [observational-astronomy]

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

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### Attempting to plot solar terminator using Python and Skyfield library

Problem I would like to plot the small circle defining the visible portion of Earth for an observer at position $P$ away from the Earth, on a 2D map. In the case of the Sun, this would be the solar ...
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### Do the stars on the mantle match some constellations? [closed]

My question is: unwrap the 3-d star-points on the mantle to a 2-d star- points; to see if the star-points match some constellation in the sky? In unwrapping the mantle and holding it up towards the ...
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### Calculate geographical location (latitude, longitude) from horizontal and equatorial coordinates, date and UT

Lets say I found myself in the middle of nowhere with small computer with some sort of offline astrometry engine (like locally installed astrometry.net). I have some sort of mount that precisely tells ...
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### For detection of distant galaxies by gravitational lensing-induced magnification, roughly what are the distance ratios from the lensing systems?

Discussion in comments under the question Does seeing a gravitationally lensed/magnified galaxy imply that they could also see us as well? have got me wondering about the geometry behind detection of ...
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### how much does 1 second of error impact sidereal tracking?

Usually observatories have time servers on site for reasonable time keeping. If I have 1 second of time error, how will this impact sidereal tracking? By how much?
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### Does seeing a gravitationally lensed/magnified galaxy imply that they could also see us as well?

Does an observer in that galaxy see our galaxy magnified as well?
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### How to obtain the distance to a particular stellar cluster from GAIADR3 data? [closed]

I am trying to obtain distance towards a Galactic IR bubble. I took the data of all stars in that region from the GAIADR3 catalogue and tried to figure out if there are any stellar clusters. I found ...
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### Why is v lowercase and D uppercase in $v=H_0D$?

Why is v almost always written in lowercase and D in uppercase in $v=H_0D$? OK, v is in lowercase, as usual, but then why is D in uppercase? What's so different/special about it? In my physics school ...
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### Does a cosmological redshift occur within our local group, of galaxies?

I know that it is not supposed to be expanding but space is space and it is expanding everywhere else outside it so why not inside it too, and gravity just holds everything back. I suppose if it is, ...
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### How can Hubble's original data show that the universe is expanding?

The diagram from Hubble's original data only goes from 0 to 2 Mpc (see here), and yet our Local Group is not supposed to be expanding and it is 1.5 Mpc in radius. How can the data show that the ...
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### What is the name of this eclipse cycle (if there is one)?

Today I navigated to Wikipedia's "Eclipse Cycle" page and found that they had updated their table of eclipse cycles with many more named cycles. However, one particular cycle that I had ...
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### Is there a noob-friendly website/app for tracking a astronomical body's apparent movement over time?

As I walk home along my road most nights in winter, I see the Moon and one-or-more planets. Unsurprisingly, over the last 2 months, if it's been the same planet and it (and the Moon) has been in ...
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### Was this video shot with a ground based hobby astronomer telescope?

I stumbled across this video capturing the rings of Saturn and wanted an expert opinion. This video of Saturn looks so good that I was wondering if it was really shot by a hobby astronomer's telescope ...
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### What is the solar diameter?

What is the solar diameter in SI units? Google tells me this is 1.3927 Gm. How accurate is that figure? I am looking for estimates with referenced data and calculations, and the uncertainties: due to ...
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### What were the specifics of the photos taken by Sir Arthur Eddington during the Eddington expedition that supported Einstein's Theory

I know that Sir Arthur Eddington went to South American to photograph stars around an eclipse to see if they seemed to change position when the light past by the Sun relative to when the light didn't ...
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### Can a meteor streak exhibit different colors denoting presence of more than1 element?

A meteoroid's elemental composition can be determined by the color it exhibits while burning in the earth's atmosphere which we also call a "meteor". However, is it possible that a meteor ...
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### How to decide and narrow down the broad topics I should get an astronomy internship on? [closed]

This is to inform that I am a third-year Physics Major student. I am enrolled in a five-year dual degree BS-MS programme at IISER Bhopal, India. I had a keen pop-science-like interest in astronomy ...
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### Can Alpha Centauri be observed from Eilat Israel, and if so when and for how long?

Wikipedia states that Alpha Centauri is the third brightest star, outshone by only Sirius and Canopus, and can be observed from latitudes south of ABOUT 29°N. With Eilat listed at 29°33′25″N, are the ...
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### How do you calculate the reddening corrections for photometry?

I have photometric data from Gaia for a star and am trying to de-redden the colors. I need to find the reddening corrections for the photometry. I have photometry for G, BP, and RP. To start I am ...
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### Can terrestrial infrared telescopes see through clouds or haze, sometimes at least?

My answer to Could UV-A imaging sensor reasonably see a total eclipse in progress through clouds? suggests that while clouds blocking visible light observation of the (partially) eclipsed solar disk ...
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### Geometric effect on sun's position in the sky at the equator

This question is about an explanation of "Sunrise and Sunset Times Near the Solstices" on the official website of the US Naval Observatory. It is mentioned in the explanation article that, ...
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1 vote
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### How do you convert from the Gaia photometric system to Johnson-Cousin?

I have Gaia photometry (G, G_bp, and G_rp) and need to convert it to the Johnson Cousin system. In the Data release 3 (DR3) documentation they provide tables of how to do this but I’m very confused by ...
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### Why is intensity not an observable quantity?

I found that in astronomy we usually use flux $F$ instead of intensity $I$ in observations. My teacher tells me it is because intensity is not a observable quantity. So why can we only measure flux, ...
1 vote
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### Shooting fire ball in the sky

I’m hoping someone out there can answer a lifelong question that’s bugged me for years. I’m 60 now and always wondered what me and my friend saw back in the 70s in Windsor, UK. We were going early ...
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### How was the size of the earth determined 100/200/300 years ago?

How was the size of the earth determined 100/200/300 years ago? I know that by then the had better methods then the simple sticks and shadow experiment.
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### Just wondering if anybody knows how to do this question about angular resolution of the human eye?

Estimate the angular resolution of the human eye at the centre of the visible wavelength range during daylight. Using your answer, estimate the surface den- sity of rods (per mm2) on the retina, ...
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### What star is this?

From this image, can you help me identify the star circled in yellow? This picture was taken mostly above my head, but facing slightly southeast, from the southwestern corner of Virginia.
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### What can be learned by observing tumbling asteroid 319 Leona passing in front of Betelgeuse's fickle photocenter? What campaigns have been organized?

There's a lot of interest in Betelgeuse party because of it's recent fainting behavior, and despite being so close, the huge uncertainty in it's distance due to its fickle photocenter: Can New ...
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### Just how resonant is the "resonant sextuplet of sub-Neptunes transiting the bright star HD 110067"?

The November 29, 2023 arXiv preprint A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067 constructs a resonant chain of orbital periods based on mean motion resonances (MMRs) and ...
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### How to calculate 2-10keV Flux or Luminosity by Power Law from 0.2-12keV with known $\Gamma = 1.7$

I have $0.2-12$keV flux observations, distance observations and $\Gamma =1.7$. I want to apply power law to calculate 2-10keV flux. How can i do that?
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### How to convert flux to flux density for a synthetic spectrum?

I have several model SEDs generated by the CLOUDY spectral synthesis code. The data is formatted with one wavelength column and one flux column. I wish to perform Hubble synthetic photometry on these ...
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### Calculate change in spectral line intensity for a change in temperature

I am trying to do some simple modelling of spectral line emission. I am starting with some ALMA observations of a protoplanetary disk, where the emission from a particular molecule at frequency 344GHz ...
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### Should you include aberration effects during low Earth orbit observations?

I am working on calibration of some observations of low Earth orbit satellites and I am wondering should I include aberration effects? My logic is that diurnal aberration would have neglegible ...
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### Formula for rate of expansion of the universe vs distance?

How does the distance $r$ scale with the expansion of the universe?For example if $r_{o}$ is the distance between us and a galaxy and $V(r_{o})$ is the rate of expansion of the universe at that ...
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### Where can i find dark frames in the ESO archive?

I am doing an image reduction with data from ESO but I can't find dark frames when I download the zip-folder even though I downloaded the associated callibration files. The image reduction I am doing ...
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### If 42000 Starlink satellites interfere with telescope observations from Earth would someone observing from another solar system detect them too?

SpaceX's Starlink constellation could place up to 42000 satellites around the Earth. Would aliens with their own telescopes notice them? They would be about 150 km apart and could reflect light of ...
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### Why is the H-alpha line slightly shorter in wavelength (656.28 nm) in air than in vacuum (656.46 nm)? Shouldn't it be longer?

Perhaps this is a question better suited for Physics SE, but since the H-alpha line is so important in astronomy, I'm posting this here.... I would, naively, assume that wavelengths would be longer, ...
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I’m wondering about the abilities of a technology: You may have heard of the Square Kilometer Array. The array is focused by adjusting the timing of the individual antennas. Q: Could this array be ...
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### Astro-filters for the solar system

I’m looking for set of filters for my telescope. Something for the solar system. Can you say me what is the best choice?
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### How can the new moon set before the sun, as will happen in some locales on November 13, 2023?

I have somewhat of an interest in sighting the new moon. I recently heard a lecture by someone who had written a program to provide the conditions for the first new moon sighting for any location for ...
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### Which place in the world should be best for astronomy with an optical telescope?

Would it be somewhere in a desert a long way from water and mist, or high on a mountain above the lower atmosphere? Where is the best location in theory or in practice?
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### Are there plans to detect life on Earth from the outer solar system?

This has been kicking around in my head for a while. We've been detecting planets for decades by observing regular dips in starlight from many light years away as a planet transits its host star. I've ...
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### Do the discs of observed solar systems have random orientations?

Is there any bias in the orientation of solar systems?
1 vote
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### How do eyepiece mm values equate to telescope tube extension mm values?

I'm trying out a DSLR on my Celestron 70EQ refractor telescope with a DSLR T-ring. The first try didn't magnify very much, and I learned that I need to extend the focus length to magnify the image; I'...
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### For what period of time can planets be viewed from the North Pole as just being there?

I would like details on observations (since North Pole is not possible, approximately around the North Pole) which tell us for how long are planets visible from the North Pole? I understand that ...
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I'm a student, I am doing an investigation about S0-2. My idea was to take the wavelength that emanates from the star. When I saw the data from Science magazine I found a problem that was that the ...
1 vote
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### Gas mass and velocity in galaxy

I was going through the SPARC data on galaxies (http://astroweb.cwru.edu/SPARC/) The velocity of gas in the SPARC data is in http://astroweb.cwru.edu/SPARC/MassModels_Lelli2016c.mrt The gas velocity ...
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### Why is plasma used to deposit aluminum on the VLT's four large mirrors?

In Tim Scott's October 2, 2023 video "The largest telescope that will ever be built*" (note the asterisk, link below) there is a discussion of the "re-silvering" of the four main ...
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1 vote