# Questions tagged [observational-astronomy]

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

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### Which approximations are required for the synodic period formula?

The formula below is used to calculate the synodic period between two bodies orbiting a same third one: $$\dfrac{1}{T_\mathrm{syn}} = \dfrac{1}{T_{1}} - \dfrac{1}{T_{2}}$$ This formula can be used, ...
649 views

### What is the composition of the Solar Wind?

Is the composition of the Solar Wind known? I'm especially interested in the heavy metals present. Most accounts deny the existence of anything other than electrons, protons, and some alpha particles; ...
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### Calculating orbits using observational data

How did astronomers in the 18th and 19th centuries used to calculate a comet's or planet's orbit using observational data, given that this data is relative to a non static reference point (i.e. the ...
1k views

### Angles of sunrise and sunset viewed from a surface anyway oriented

I need to understand how to calculate the angles of the sunrise and sunset viewed from a surface oriented against the azimuth and the horizon plane, and for any day of the year. For example, I have ...
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### Observations of a perigee coincident with a full Moon

Hopefully this will be a quick and easy question, with a quick and easy answer, but why is it that we observe a perigee Moon coincident with a full Moon approximately every 13 months? Is this related ...
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1 vote
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### How to find out which Messier objects are in the Kepler/K2 fields?

I am interested in figuring out which Messier globular clusters (plus 47 Tuc and Omega Cen) are in the Kepler/K2 fields, both fields that have already been observed and any that will be observed. ...
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1 vote
588 views

### Galaxy behind the Ring Nebula

Would anyone be able to reference the galaxy in the background of this image of the Ring Nebula: It's obviously not a Messier object, I'm more confident in it being in the New General Catalogue.
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### On the lack of observational records by European astronomers of the 1054 guest star

This question relates to the Crab nebula, the Crab Pulsar and the known concurrent supernovae event as recorded by Chinese astronomers in 1054. I'm wondering, I'm looking at the history of the ...
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### In SETI has anyone calculated an estimate of the mean time between observations?

So the Drake Equation, proposed by Frank Drake, is often cited as a means to estimate the number of intelligent civilizations that exist in the observable universe. Initial calculations by Drake ...
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### Percentage of charted stars

I was reading Gene Roddenberry's guide for TNG writers and he mentions that that the time of ST:TOS, only 4% of the stars in our galaxy have been charted; this goes up to 19% by the time of TNG. This ...
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### How bright will Sirius be when it's closest to the solar system? [closed]

Preferably in terms of percentage. As a layman, visual apparent magnitude means little to me.
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### How many science instruments can be used in parallel with the Hubble Space Telescope?

The Hubble Space Telescope offers a parallel obervation mode. Observing programmes such as CANDELS and CLASH use WFC3 and ACS in parallel fields. These are also the only instruments of which I have ...
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### What telescopes have observed anomalies in the light curve of Tabby's star, KIC 8462852?

KIC 8462852, the F-star that inexplicably dims by up to 20% for short periods, is still getting alot of attention. A slow continuous dimming by about 0.3% a year has been identified recently. But all ...
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### (How) Can one determine if an exoplanet is synchronously tidally locked or not? [duplicate]

Mercury is asynchronously tidally locked so that all of its surface regularly sees the Sun. But an exoplanet which is synchronously locked to its star, could we tell that it is? It would have a hot ...
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### Could non-supernova carbon, oxygen, or silicon flashes be observed?

I was reading about the helium flash, the short but sudden onset of helium fusion in certain red giant stars. As I understand, the upper (nondegenerate) layers of the star absorb the energy as they ...
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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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### More than 67 Jovian moons?

Wikipedia says that there are now 67 known moons of Jupiter. It got me wondering: is it really possible in our day and age that there are more, but we haven't observed them yet? On the other hand, ...
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### Is remote measurement of isotope ratios possible, or must a sample be aquired

Is it possible to measure to measure isotopic abundance of remote astronomical objects - ie measurement without having a sample to feed into a mass spectrometer? Do different isotopes show any ...
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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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### Are there any reliable optical measurements of the radius of a neutron star?

I know that there is plenty of theory to predict the size of a neutron star: my question is whether or not there are any reliable size estimates based on observation. Please note that, to be reliable,...
258 views

### Is Planet Nine observable in principle?

Is so-called Planet Nine (given it exists) observable in principle? By "observable in principle", I mean "if we knew exactly where to look, would we be able (from a technological standpoint) to get an ...
133 views

### Why the light curve goes down when the planet is behind the star?

There is a video explaing the transiting exoplanet light curve — https://www.youtube.com/watch?v=RrusIZaWDW8 It is clear to my why the curve goes down when the planet is between the observer and the ...
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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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### How do I apply a velocity shift to a wavelength array with uniform logarithmic spacing?

Suppose I have a wavelength array for a spectrum in units of Angstroms. Suppose further that the wavelength has "uniform logarithmic spacing" such that if I just take the difference in Angstroms ...
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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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### How long do hot X-ray sources last?

Some X-ray sources in nebulae are caused by hot materials in the millions of degrees that formed in supernovae. What's the cooling rate of this stuff? How long does it stay this hot? If we would take ...
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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 ...
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1 vote
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### SDSS Image FITS files have negative values. What do these negative values mean?

I am new to using SDSS image files and have noticed that some of the values in the FITS file are negative. Can somebody explain to me what these values actually mean?
1 vote
188 views

### What does the filter name I+z' mean

On the TRAPPIST telescope, the filter wheels are described to have a filter with the following description: NIR Luminance I+z' (>700nm) After a bit of googling, I wasn't able to find what the ...
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### UTC to UT1 time corrections

Astronomic observations in geodesy. It is well understood that sun and star positions may be expressed in Greenwich hour angle and declination. Or Right Ascension Declination. And may be published ...
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### Moving-Cluster method for determination of the distance of Hyades. A starter problem

I am currently following a class of observational astronomy lab. I will present a brief description of the method in first and then proceed to the question, so anyone is welcomed to read the entire ...
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### How many stars are there in a Globular Cluster of 10^5 solar masses?

I was wondering whether there is an easy way to approximate the number of stars in a Globular Cluster (GC) with 10^5 solar masses. Can one, for instance just assume the GC is made of sun-like stars ...
878 views

### Why aren't ground-based observatories using adaptive optics for visible wavelengths (circa 2016)?

Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing. The atmospheric effects are quite ...
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### 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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### Pinhole projector for the Transit of Mercury

Very quick and simple one today. What would be the best/optimal pinhole size for a pinhole projector to observe the transit of Mercury on May 9th? I want to get the optimum between resolution and ...
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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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### Why would astronomers want to eclipse the Sun?

I've heard that some astronomers are building an artifical solar-eclipse ship, that should help us to dim the diffraction of the Sun. Why don't we just wait till night? What is the function of the ...
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### How can apparent magnitude be negative?

What is the reason for that scale? Is it because otherwise defining an maximum would be too hard(?). Why do objects that are (apparently) brighter get assigned a smaller number (and down to negative)?
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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 ...
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### How Soon Could a Waxing Crescent Moon Be Seen?

Question: Apart from a Solar Eclipse, How much time is needed until a Waxing Crescent Moon be seen following a New Moon? Would the time of year be significant? The Vernal Equinox + 1 Month. Could it ...
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### Parabolic or hyperbolic trajectories

According to Newton's laws, the trajectories for the two-body problem are conics: either ellipses, or parabolas or hyperbolas. Of course periodic motions require Ellipses and in the Solar system these ...
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### Given a collection of pixels, how to deduce the flux from them?

I've obtained the coordinates of brightest pixels from different images (.fits files) using Python. I want to get the flux of each pixel. How do I go about finding out the flux?
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### Moon SHAPE calculator

I have seen a lot of information about moon phase calculation, but need an accurate moon shape calculator/algorithm given the observer's position and time. This implies that the illuminated portion ...
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### Color of planets

I am developing an astronomy software and need to know the color of each planet in the Solar System, when observed with the naked eye. I cannot find that information after googling for a while. Is ...
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### 3000th Question: What does the future of astronomy look like with the next generation of telescopes? [closed]

What will the benefits and advantages be of the upcoming generation of telescopes such as LSST, E-ELT and JWST? And more broadly where will this leave astronomy in 10-20 years time? This isn't a ...
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### What is the schedule for science runs of aLIGO (and VIRGO)?

Advanced LIGO seems to operate only intermittently. Is there a schedule for at what times it will be able to register new gravity waves? Even if no formal schedule is available, what main factors ...
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### SDSS. Google Sky and DeCaLs

(1) Please go through following image Possible Super Red Giant? However sdss shows it as galaxy! Am I missing something. (2) Google Sky shows object in latitude and logitude format like this. Is ...
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### Could science be lost if a phenomena is observed before predicted? [closed]

An observation could validate the predictions made by a previous theory. If something unpredicted is observed, then a new theory which is compatible with the observation should make predictions which ...
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### What methods exist to calculate the ellipticity of galaxies

What methods exist to calculate the ellipticity of galaxies and what are their drawbacks? I have asked this question about ellipticity in the SDSS but I want to know about general methods for cases ...
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