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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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16 votes
2 answers
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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 ...
uhoh's user avatar
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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
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1 vote
1 answer
232 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
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6 votes
1 answer
622 views

Where might astrometric observations of the Roadster spacecraft be catalogued?

above: (see small red lines near center of image) Tesla Roadster. 18 Feb. 2018, 11:28 UT. The image above comes from the average of ten, 300-seconds exposures, remotely taken with the 16”-f/3.75 ...
uhoh's user avatar
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4 votes
1 answer
143 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
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4 votes
1 answer
551 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
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4 votes
3 answers
942 views

Measuring misalignment between two positions on sky

Let's say I have the (RA,Dec) for two positions on the sky. I want to measure the position angle between these two positions. In other words, if I had the Cartesian coordinate vectors for these two ...
quantumflash's user avatar
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
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13 votes
2 answers
2k views

How does angular resolution of a telescope translate to its parallax precision?

We can often read in the scientific and also more casual reader literature and articles about the angular resolution of various telescopes and other optical equipment, be it ground based or onboard ...
TildalWave's user avatar
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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
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4 votes
2 answers
548 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
3 votes
1 answer
903 views

Transform pixel coordinates (in FITS file) to equatorial

Say I have a FITS file with an observed field of stars, each one with x,y coordinates given in pixels. Assume the image is aligned so that the x axis is the right ascension, and the y axis the ...
Gabriel's user avatar
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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
1 vote
2 answers
467 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
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1 vote
0 answers
97 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
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1 vote
1 answer
424 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
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1 vote
1 answer
1k views

Open access table of visible stars with magnitude, coordinates, and possibly color?

I'm looking for a link to a table of visible stars that is open and available to everyone. It should have magnitude, RA, dec, and possibly some indication of color. This will be used to produce ...
uhoh's user avatar
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1 vote
0 answers
240 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