Questions tagged [observational-astronomy]

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

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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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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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What kind of Engine used in Rockets in zero gravity [closed]

What kind of Engine used in Rockets when they move in Horizontal direction on zero gravity... And How it works?
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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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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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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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Has optical interferometry been done at radio frequency using heterodyning with a laser in a nonlinear material?

If I collected narrow band optical emission from a large telescope with frequency $f_1$ and mixed it in a nonlinear crystal with laser light of a nearby frequency $f_2$, it would produce two new ...
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1answer
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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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1answer
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What direction does 0° in the J2000 epoch point towards on January 1, 2000?

Is 0 degrees in the J2000 Epoch 'right ascension' is a line from Earth to the sun on January 1, 2000? Or is 0 degrees the direction towards the ascending node 'equinox'? Which is NOT towards the Sun ...
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Why is detecting brown dwarfs difficult?

Why is detecting brown dwarf stars tedious and not always successful? They emit light in the infrared region, and given that we're surrounded by state-of-the-art technology in space today, why haven't ...
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Why is there no Proxima 'a' planet? I'm confused about the naming convention [duplicate]

Why is there no exoplanet around Proxima Centauri designated with the letter 'a'? There is, famously, a 'b' and now a newly confirmed 'c'.... I have read that exoplanets around a star are designated ...
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Different times of sunset at the same location due to elevation

Me and my friend were watching the sunset on the same location (at my country the latitude is approximately 40 degrees). I am at sea level and my friend is at an elevation. He observed the sunset with ...
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1answer
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Map planetary eccentricity on a perfect circle? [closed]

What is the formula to plot an eccentric orbit on a perfect circle? I have estimated the full degrees each planet would occupy on a 360 degree wheel (natal chart) but how do I take into account a ...
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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 ...
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Emission Line Galaxies(ELGs) selection using narrow band

I selected ELGs using the z BroadBand and NB921 narrow band according to the condition of Hayashi+11 Then I plot the transmission curve of the filters used, I got this As we can see NB921 and NB926 ...
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1answer
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What are the things, the hobby astronomers observe? [closed]

I was thinking: What are the things, that hobby astronomers observe? (Things, that are in the domain of astronomy and hobby.) I tried some googling, and I found just what do professional ...
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1answer
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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 ...
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2answers
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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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1answer
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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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1answer
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Flux density from brightness map

This is a naive question. I have a temperature map of radio emission at 1420 MHz, in Kelvin. I want to extract the flux density (in Janskys) from an extended region of this map. Is the flux density ($...
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Ladakh India where the moon (Ramadan moon) is sighted but not in rest of India [duplicate]

Today 22 May 2020 around 3 p.m Ladakh India sighted new moon(Ramadan moon) but not in rest of India.I read many articles acc. To them it is not visible today, then how it was seen from Ladakh... .
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1answer
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Why is SWAN dimming?

The SWAN C/2020 F8 comet is passing near the Earth, but from Wikipedia The comet has dimmed a small amount since May 3. It was expected to possibly reach 3rd magnitude in May, but is now expected to ...
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Hello again, Barlow Lenses

I am debating if I should buy a 2x Barlow Lens. My telescope, a go-to Meade star navigator, has an aperture of 114mm, focal length of 1000mm and I currently have a 9 and 26mm eyepieces. I want to see ...
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Longest time after an image was taken when a new solar system body was discovered from it?

This answer to If there's nothing special about Pluto, why was it discovered so early? says: In fact, often objects are discovered to be in pictures from long ago, such as Orcus, discovered in 2004,...
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What are the necessary steps required for calculating the size of a star? [closed]

Title pretty much says it all. Basically, what exact variables are used, and what steps need to be taken, in the calculation of the size of a star? Preferably, some example data for how a the size of ...
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How does the Astronomical Twilight depend on the night length or the day length?

Some references say that the Astronomical Twilight starts at the last 1/8th of the night length, so it is long in Winter and short in Summer; But by using the 18 angle (sun elevation below the ...
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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 ...
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1answer
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Options for observational astronomy [closed]

For getting into a PhD program for observational astronomy, is physics major and data science minor enough?
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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 ...
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What's the highest frequency that's been imaged by a radio telescope?

In this answer to Should we update definitions and remove the 100 GHz hard limits on radio astronomy related tags? I wrote the following partial answer: Yes, there are plenty of dishes that focus ...
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1answer
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Is there any way to seperate astronomical and instrumental objects?

Here is a image of hcg79 taken from APO. I'm just curious if there is any way to seperate astronomical and instrumental features in this picture? Thank you.
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1answer
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How is Cosmic Microwave Background's temperature measured?

How do Cosmic Microwave Background missions/telescopes measure CMB temperatures? I understand that CMB has Planck's spectrum. So I was thinking one strategy could be to measure the spectral radiance ...
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How to select galaxy emitters from color-color diagram? (Those candidates which are above a line in a plot)

I am trying to select the OII emitters from the colour-colour diagram of galaxies data. I don't know how to select those candidates which are above the line. Here is my colour-colour diagram. . What I ...
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1answer
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How does diffraction occur in a reflecting telescope?

It's understandable how diffraction occurs in refracting telescopes, because the lens itself is a small aperture for light to pass through. But what about reflecting telescopes? Since light is ...
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4answers
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How do focal length, angular magnification and field of view relate?

The larger the focal length the larger the angular magnification The smaller the focal length the larger the field of view. I don't understand why this applies. I'm talking specifically about ...
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2answers
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Why are Cassegrain telescopes shorter than Newtonian reflecting telescopes?

Many websites say this is because the effective focal length of the objective is increased by making the secondary mirror convex. This allows a Cassegrain telescope to be shorter than a similarly ...
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1answer
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Brightness, altitude & azimuth for satellites?

I'm using the heavens-above website to identify a satellite I've seen several nights this week. The question is related to how I can search the satellites table with the information I can provide. ...
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1answer
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Can the interferometer called “Gravity” measure “a few centimeters on the Moon”?

Phys.org's Very Large Telescope sees star dance around supermassive black hole, proves Einstein right links to several ESO videos, including Interview with Reinhard Genzel (in English). After ...
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1answer
103 views

How low can the sun be seen in the sky?

I'm interested in knowing how low the sun could ever get in the sky and still be seen. More technically: what's the minimum possible elevation of the sun at which it can still be seen above the ...
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Detect sources near image edge with python photutils

As my question suggests, I 'm trying to use a python library photutils in order to detect sources from MUSE cube. MUSE (Multi Unit Spectroscopic Explorer) is an ...
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1answer
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Calculating Field of View of a Telescope Given Time of Another Object

Given the celestial coordinates of a certain star and the time it takes to pass across your telescope's eyepiece, how can you calculate the field of view of the telescope?
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Distance to star using color index

I'm doing the following question: A star is observed with UBV magnitudes $m_u = 16.31$, $m_b = 14.52$, $m_v = 13.76$. Spectral analysis gives $M_{bol} = 7.31$, $BC = -1.02$, $(U − B)_0 = 1.222$. ...
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What is the highest redshift a galaxy with a known stellar mass can be observed?

As part of my research, I would need the following information which it seems I cannot find it in literature. I would like to know what are the highest redshifts at which $10^{7}$, $10^{8}$, and $10^{...
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Moving objects in the sky tonight 27th March 2020 [duplicate]

Multiple moving objects not in a line. The are staggered single line and in groups of two or three. One or two moved downward. They had a dim light orangey colour. It was not obvious that these ...
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Betelgeuse problem

I've been given this problem: (a) A telescope is required to image an area of the sky of angular size 1 arc second onto a 10 mm square CCD. What focal length must the telescope mirror have to fully ...
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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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Why were solar constant measurements before TSIS-1 all about 0.3% high?

Phys.org's Solar energy tracker powers down after 17 years says: "The big surprise with TSI was that the amount of irradiance it measured was 4.6 watts per square meter less than what was ...
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Was the “green star” event in NGC 3314 ever figured out or named?

from NGC 3314 Variable Object by By Bill Keel (University of Alabama, Tuscaloosa) and Lisa Frattare (Hubble Heritage Project, STScI). The object in question is circled. Comments below this answer led ...
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Can I use the parallax coefficients for observatories as a proxy for latitude using arctan2(sin, cos)?

In How are the three character IAU Minor Planet Center's Observatory Codes assigned? Why are some letters so popular? I looked at the distribution of the first alphanumeric character versus the value ...
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1answer
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Visible satellites real time position API

I'm trying to obtain the azimuth and elevation of all (or at least the majority) visible artificial satellites from a given latitude and longitude. Is there a quite stable API that does that for free? ...

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