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Questions tagged [astrometry]

Questions about the measuring the position of stars, and the techniques used to do this.

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6 votes
1 answer
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Has earthshine in fact increased since lights (say 1900); that is to say can we measure or has there been a measurable increase? What are the numbers?

Three questions, How would, or how is commonly, earthshine best stated (absolute magnitude, overall watts from the lunar surface, or?). (Further, since the moon is irregularly shiny is it measured ...
Fattie's user avatar
  • 946
1 vote
0 answers
72 views

Declinations from stars apparent motion w/o plate solving

I am trying to program the calculation of the declination of the stars, based on their apparent movement through a series of astrophotographs, purely algebraically, without using a solver based on the ...
Danko Dnevic's user avatar
1 vote
1 answer
93 views

What is the explanation for discrepancies in RA values at Santa Maria Degli Angeli e dei Martiri in Rome

There is a meridian line in the floor of this church in Rome: http://www.santamariadegliangeliroma.it/paginamastersing.html?codice_url=La_Meridana& I took this photograph which shows the inlaid ...
Theo H's user avatar
  • 113
2 votes
2 answers
134 views

Determing timestamp of a photo of the stars using a plate solver

This question from 2016 seems to suggest that you need a powerful telescope to get a photo of the stars in such a way that you can use their proper motion to get a timestamp. If this is possible, how ...
requiemman's user avatar
1 vote
0 answers
47 views

On building a compatible pipeline for astrometry using both Gaia or Vera-Rubin's data

As the title states, I'm considering building a pipeline for astrometry to analyze Gaia and Vera Rubin's data. As, being honest, I have little experience with astrometry, I'm not sure if this is (or ...
nuwe's user avatar
  • 771
1 vote
1 answer
66 views

Moon's libration from Mathematica data

Wolfram Mathematica provides "TransitTime" option (for the Moon in particular). Knowing this time moment, you can get the position of the moon at upper culmination (for example, for each day ...
lesobrod's user avatar
  • 123
3 votes
3 answers
184 views

Reverse polynomial model for reverse astrometry

I have a polynomial model that can transform pixel X,Y coordinates to standard $\xi, \eta$. This model looks like this: $\xi/\eta = a_1 + a_2x + a_3y + a_4x^2 + a_5xy + a_6y^2 + a_7x^3 + a_8x^2y+a_9xy^...
jlipinski's user avatar
  • 309
2 votes
1 answer
94 views

Transformation matrices and their derivation (if possible) for ICRS frame for reference to other frames

I am finishing up my thesis write up and one of the chapters in my thesis is on astronomical coordinate systems since in my analysis of data I have converted the available astrometry from the ICRS ...
CTZenScientist's user avatar
5 votes
3 answers
347 views

Why don't we use the Voyager/Pioneer etc space probes to measure stellar parallax?

With Earth based telescopes you get a max distance of 2 au between measurements. While we have multiple space probes well over 100 AU away from us, that's a 2 OoM difference.
blademan9999's user avatar
1 vote
1 answer
80 views

Do astronomical datasets exist that receive duplicates or are there multiple datasets that contain the same entities (stars)?

I am currently doing my PhD in computer science, and I have almost no astronomical knowledge. I am currently researching on duplicate detection in databases (so detection of multiple entries referring ...
Lasklu's user avatar
  • 21
2 votes
0 answers
61 views

How to reduce Hipparcos catalog star coordinates to another Epoch?

Hipparcos catalog lists star equatorial coordinates (RA,Decl). The coordinates are 1991.25 positions on ICRS reference frame (epoch J2000). According to Astronomical Algorithms (J. Meeus) the ...
Omar Reis's user avatar
3 votes
1 answer
262 views

Radial velocity

Is there a way to calculate the radial velocity without wavelength? I can only find two formulas so far. One of them needs wavelengths and the other one needs the velocity of the star, but I have none ...
C H's user avatar
  • 71
3 votes
1 answer
422 views

Why does the altitude-azimuth mount have a blind spot near zenith?

I understand the subject mathematically. Azimuth of the celestrial object under track changes a finite 180 degrees instead of a infinitesimal amount as the body passes zenith. This would require ...
Cici Xu's user avatar
  • 31
5 votes
0 answers
134 views

Positional astronomy - Speed of the sun in sky

Let $\vec{r}$ be the position of the Sun in the sky, from Earth. How could I estimate the magnitude of $d\vec{r}/dt$, to measure the rate of change in time of the arc it traces? I suppose it would be ...
nuwe's user avatar
  • 771
1 vote
0 answers
52 views

Calculating the angular momentum of stars from Gaia archive (Gaia DR3)

I am trying to calculate the angular momentum for a subset of stars from Gaia DR3. I have scanned the available fields in their database and could only find out the below fields that specifies the ...
CTZenScientist's user avatar
4 votes
1 answer
173 views

How can I replicate AstroImageJ's pixel to RA/Dec algorithm in my own code?

EDIT: solved, thanks to Eric Jensen's suggestion (in a comment on his answer) that I include the correction to my right ascension value as a function of my declination. All other comments were helpful ...
Conor W's user avatar
  • 43
4 votes
0 answers
128 views

Is there a website or app that can add declination and RA grid to an existing photo?

For a few years now, I've been shooting photos of the night sky with just a tripod and my Nikon DSLR. After extensive post-processing to mitigate light pollution, I usually submit the final results ...
user382459's user avatar
2 votes
1 answer
690 views

Celestial coordinates of every pixel in the image

I am solving starfield using Astrometry.net, an amazing piece of software I must say. After solving the starfield, Astrometry gives celestial coordinates of centroids of every star in the image, as ...
Falco Peregrinus's user avatar
6 votes
0 answers
136 views

Airy's Water Filled Telescope: help required to fully understand the calibration procedure followed

I am reading/studying the instrument description of Airy's Water Filled Telescope (Airy, G. B., "History and Description of the Water Telescope of the Royal Observatory, Greenwich", ...
JKrsl's user avatar
  • 121
4 votes
1 answer
1k views

Practical ways of measuring the sun-earth-moon angle?

I learned as a child (and a common tale), that Aristarchus gave a method of measuring the sun-earth-moon angle to estimate the ratio of the earth-moon distance to the earth-sun distance. Indeed, ...
bonsoon's user avatar
  • 143
2 votes
2 answers
1k views

What exactly is the orbital period value of Sirius binary star system?

My Textbook An Introduction to Modern Astrophysics 2nd edition (2017), page 557 mentions that the modern value is 49.9 years. But Wikipedia mentions 50.1284±0.0043 years. Which is correct? Or, has the ...
James Smith's user avatar
1 vote
0 answers
246 views

Relationships between G magnitude, Johnson V magnitude, and spectral type of stars?

I'm simulating a population of binary stars for a summer research project. I'm adding uncertainties to my simulated observables such as angular position and radial (line of sight) velocity. I'm using ...
Sofia Splawska's user avatar
4 votes
2 answers
554 views

How to actually obtain the parallax angles that are used to determine distances of stars?

I’m trying to understand how to measure the distance to nearby stars using the parallax method. My question is: how do you get the value of the p angle?
codependent's user avatar
4 votes
2 answers
1k views

Plotting Equatorial coordinates to X,Y plane (simulating telescope/camera view)

I would like to simulate a telescope camera view, projecting (RA, Dec) coordinate sets to a 2D plane. So effectively the need is to convert Equatorial coordinates to (x, y) coordinates, when we can ...
AstroDuck's user avatar
4 votes
2 answers
293 views

What is the mean separation between a star and its closest neighbor in the Milky Way halo?

My question is inspired by this previous question, Are there any stars that orbit perpendicular to the Milky Way's galactic plane?. In the great answer posted by @ConnorGarcia, one commenter said he ...
ksousa's user avatar
  • 1,201
0 votes
0 answers
82 views

Setting specific CENTER coordinates coordinate in SWARP

The SWARP Documentation specifies that we first set the CENTER_TYPE to MANUAL and then in the CENTER parameter we specify either one of the equatorial coordinates (RA, Dec). This is specified in the ...
Hiba Jamal's user avatar
3 votes
1 answer
143 views

What measurements helped us in understanding 'Oumuamua's location and speed?

What measurements helped scientists understand 'Oumuamua's location and speed? I wanted to know how it was achieved and with what accuracy if possible.
Mahen's user avatar
  • 73
4 votes
1 answer
145 views

How often are radio telescopes used to measure parallax? When was this first done?

The abstract of A magnetar parallax (also in MNRAS) says: TE J1810-197 (J1810) was the first magnetar identified to emit radio pulses, and has been extensively studied during a radio-bright phase in ...
uhoh's user avatar
  • 30.7k
8 votes
1 answer
612 views

Are we less safe now that Arecibo is no more?

update 3: uhoh! Source: Reddit update 2: Sadly, parts of the dish have collapsed, several cables have snapped, and the Arecibo radio telescope is now decommissioned and demolition has been ...
uhoh's user avatar
  • 30.7k
1 vote
1 answer
233 views

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 ...
uhoh's user avatar
  • 30.7k
0 votes
0 answers
338 views

Position Angle Relative to North

I am trying to find the position angle of a star whose Ra and dec are known. I have already looked at the 'Measuring misalignment between two positions on sky' question and answer, but the answer ...
Physics's user avatar
  • 101
16 votes
2 answers
2k views

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 ...
uhoh's user avatar
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0 votes
1 answer
2k views

RA and Dec of the Sun at J2000

I'm in the somewhat awkward position of asking something that, despite me thinking there should be hundreds and hundreds of web pages and datasets showing this particular value, I've been unable to ...
Izhido's user avatar
  • 103
1 vote
2 answers
684 views

In Orion, how close in local distance are the closest of the member stars?

All the members of Orion are within the Milky way, and some of them look pretty close to a neighbor. And could the bow* be an effect similar to the Radcliffe Wave? *shield
Gabe Fernandez's user avatar
5 votes
1 answer
243 views

How could one use the transit of Mercury to try and find the Astronomical Unit?

I am trying to use the transit of Mercury to estimate the distance between the Earth and the Sun, or 1 AU. I know that I need to observe mercury from two antipodes, but I do not understand any of ...
Khanrad's user avatar
  • 63
2 votes
1 answer
166 views

How was the Messenger spacecraft used to measure Mercury's orbital precession to such accuracy? Could this have been done using radar?

This comment under an answer to Path of Mercury and general relativity mentions that the Messenger spacecraft was used to measure the precession of Mercury's orbit to such accuracy that the tiny ...
uhoh's user avatar
  • 30.7k
2 votes
1 answer
2k views

how to plot sky map like www.nakedeyeplanet.com with dates tags with planetary motion path

I am curious how to plot planetary motion star chart with date tags like on www.nakedeyeplanets.com by Martin J. Powell. Is there any way to generate images similar like that. What software should ...
M10 Radalpha's user avatar
8 votes
1 answer
149 views

Anecdote of an astronomer looking for correlations in antipodal pairings of stars; what am I remembering?

The question Are the stars distributed in uniform distribution, on the celestial dome, with respect to brightness? brings to mind a different study that I vaguely remember hearing about a while ago, ...
uhoh's user avatar
  • 30.7k
12 votes
2 answers
3k views

How (the heck) does Astrometry.net work?

What magic is this? This answer to my question Astronomy detective question: what part of the sky are these photos of? What are a few of the stars? nails it, and the output (linked there) contains ...
uhoh's user avatar
  • 30.7k
2 votes
0 answers
348 views

Right Ascension, Declination from pixel coordinates

I have an Excel spreadsheet that will take certain keywords from a FITS image header. Image centre RA, Dec, rotation, x centre, y centre, x scale, y scale. I enter the pixel coordinates of an object ...
George Carey's user avatar
2 votes
1 answer
179 views

How to interpret error of absolute magnitude of a star given data from wikipedia?

This Wikipedia page contains information about the star Spica in the rightmost table. A small snapshot of this table is below. In this table, the absolute magnitude is given as ...
user avatar
4 votes
1 answer
557 views

How did they measure the distance to the center of our galaxy to 0.3% accuracy?

The abstract of A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty (Open Access) says: We present a 0.16% precise and 0.27% accurate determination of R₀, the ...
uhoh's user avatar
  • 30.7k
1 vote
0 answers
98 views

What exactly is a Right Ascension clock and how was one (mounted on a telescope) used in practice, historically?

@MikeG's answer to Why does this Lowell Observatory telescope have so many knobs? What do they all do? explains that item #6 labeled in the image there (and cropped version here) is likely to be a "...
uhoh's user avatar
  • 30.7k
2 votes
0 answers
145 views

How was the astrometry of the famous 1919 solar eclipse confirmation of General Relativity calibrated and verified?

The new New York Times article The Eclipse That Made Einstein Famous describes several events and discussions on the hundred year anniversary of the the 1919 solar eclipse and verification of the ...
uhoh's user avatar
  • 30.7k
1 vote
1 answer
433 views

How can GAIA's accuracy for position, parallax, and annual proper motion for a given star be the same number?

Per Wikipedia's Gaia (spacecraft); Objectives: Determine the position, parallax, and annual proper motion of 1 billion stars with an accuracy of about 20 microarcseconds (µas) at 15 mag, and 200 ...
uhoh's user avatar
  • 30.7k
1 vote
2 answers
469 views

How do they know how far out Farout is? (2018 VG18)

The Carnegie Science article Discovered: The Most-Distant Solar System Object Ever Observed begins: Washington, DC— A team of astronomers has discovered the most-distant body ever observed in our ...
uhoh's user avatar
  • 30.7k
2 votes
1 answer
143 views

At what latitude could Orion's belt and Aldebaran be ~10 degrees above the horizon at the same time?

In his appearance on television contained in the video The Mystery That Keeps Neil deGrasse Tyson Up At Night, in the backdrop behind astronomer and educator Neil deGrasse Tyson and the talk-show host,...
uhoh's user avatar
  • 30.7k
1 vote
0 answers
111 views

How can you estimate distance of an object by its redshift? [duplicate]

Is there a way to take the red shift of an object and, from that, calculate a rough estimate of its distance from us (in parsecs, preferably)?
Beta Decay's user avatar
2 votes
0 answers
150 views

How to calculate the various properties of a star?

I am wanting to plot a velocity profile (a plot of velocity against the star's distance from the galactic core) from the Gaia DR2, but so far my efforts have been disappointing. The information I ...
Beta Decay's user avatar
5 votes
4 answers
883 views

Measurement uncertainty of the computed center of gravity from pixel image

Establishing the position of celestial bodies (stars, and other objects) is based on imaging technology. Depending on the resolution of the imaging sensor used, an object is identified by a group of ...
Match Maker EE's user avatar