# Tag Info

13

According to the Cambridge Concise History of Astronomy (p 33 of my edition), essentially the Greeks took the (not unreasonable) view that the planets that moved more slowly were further away and were orbiting on larger spheres. That's obviously not the same as suggesting they knew "the right distances" to the planets, merely the order. They did develop a ...

10

The problem is that the apparent diameter of Betelguese is about 50 mas (milli arc seconds --- 1 mas is about 5 nano-radians) while its parallax is about 5 mas and its shape and surface brightness are both irregular and variable. Given that, the current measurement are amazingly accurate. So I can identify about three approaches to doing this measurement, ...

7

Assuming you mean the angle between the meridian line through A and the great circle that goes through points A and B, then it goes something like this. Define vectors from the origin to A and B assuming they lie on a unit sphere, such that $x_A= \cos \delta_A \cos \phi_A$, $y_A = \cos \delta_A \sin \phi_A$ and $z_A= \sin \delta_A$, and similar for B. Here ...

7

The Minor Planet Center inconspicuously puts this under "Distant Artificial Satellites Observation." DASO Circulars 561-566 have observations of the roadster 2018-017A. It's also on the short list of artificial objects for which MPC can generate ephemerides.

7

Finding an astrometric solution from an image with Astrometry.net is usually called plate solving. As mentioned in the comments, it is based on pattern matching, using a large set of databases that are pre-computed for various field of view and plate (or pixel) scale. The ArXiv paper Astrometry.net: Blind astrometric calibration of arbitrary astronomical ...

6

So the Hipparchos parallax of Betelgeuse doesn't seem accurate enough? If only someone would launch an even more advanced astrometric satellite than Hipparchos. Actually the ESA has launched an even more advanced astrometric satellite, Gaia, expected to operate from 2013 to about 2022. And it is possible that Gaia has already produced more accurate ...

6

The linked article is copied from a university press release. Arecibo's article is more matter-of-fact but naturally also emphasizes the value of their own work. NASA Goldstone can do planetary radar and remains operational. As this page says: Arecibo has twice the range and can see three times the volume of Goldstone, while Goldstone, whose greater ...

5

First you have enter your coordinates into the mount's software and then align it(e.g. 3 star alignment).After having done that, when you finish the observation you have to park the telescope. Actually Colin's answer is really helpful.They keyphrase is "After installation set up". The whole procedure should be explained in your telescope's manual. If you ...

5

The probably most advanced system for determination of parallaxes is AGIS as used for Gaia. It's able to go far beyond the angular resolution of the telescopes. Angular resolution is just one parameter. Actually it's just necessary to determine the luminosity centroids of the stars, almost independent of the resolution of the telescopes. That's mainly a ...

5

Parallax measurement in practice is not as is explained above using the popular diagram you have used. The parallax causes the star to prescribe an ellipse in the sky, the semi-major axis of whose is equal to the parallactic angle. The telescopes generally measure the shift in co-ordinates of star(RA and Dec) and then translate the information to that of ...

5

Prior to digital imaging then photographic plate negatives were analysed with scanning microdensitometers to produce astrometric catalogues. Many of these catalogues are still in use today, they are valuable sources of early epoch positions that enable proper motion measurements. For more details you could look at the descriptions of the SuperCosmos project ...

5

The orbit of star S2 is completely determined by the astrometric observations. i.e. One has the orbital period, the angular scale of the orbit and the inclination of the orbital plane. With this information alone, the distance and central mass are degenerate. If you know the distance you get the mass and vice versa. However, here the mass is not needed. ...

5

Thanks to the Mercury transit, you can measure the parallax from the Earth. That happens due to TRACE , which tracks the transit of Mercury along the polar diameter of the Earth. During that tracking, the transit of Mercury goes like that: [ Now notice that, if TRACE remained stationary, the transit would be a straight line. So, if you calculate the ...

4

The Hipparcos catalogue by van Leeuwen (2007) contains all the information you require, plus estimates of distance from parallax. It is open and free to use for scientific purposes. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I%2F311 The direct page that describes the catalogue contents and ftp site is http://cdsarc.u-strasbg.fr/viz-bin/Cat?I/311 ...

4

Telescopes will generally come with a library of objects, which includes information on where they are located on the celestial sphere. There are two important pieces of information needed for the telescope to be able to locate objects from your Earthly location - Your position so that it knows its orientation relative to the celestial sphere, and the time ...

4

Every pixel value $S_i$ on the detector at $\vec x_i$ has some error $N_i$: CCDs for example have a background noise $N_\text{bkg}$ from read-out electronics, thermal noise, and sky background, plus a Poissonian photon noise $N_S=\sqrt{S}$. In many cases this noise follows a Gaussian distribution reasonably well. After subtracting the background, a ...

4

The position angle P of a body ($\alpha_1, \delta_1$) with respect to another body ($\alpha_2, \delta_2$) can be calculated from $$tan(P)={sin(\Delta\alpha)\over cos(\delta_2)tan(\delta_1)-sin(\delta_2)cos(\Delta\alpha)}$$ where $\Delta\alpha = \alpha_1-\alpha_2$. If the denominator is negative, the position angle lies in the range of 90 to 270 degrees. ...

4

This sky configuration is consistent with 40 degrees N, at about 6.30am (local time) at the end of November. If you went to mid November, this would look the same at about 7.30am (ie 1 hour per half month). The latitude of New York is about 40N, which makes sense for a this particular US TV show, which is recorded live in New York City, "just down the ...

4

Like most asteroids and comets, 1I/'Oumuamua's trajectory was determined entirely by measuring its position in optical images over several days. The earliest data came from automated, ground-based surveys such as Pan-STARRS and the Catalina Sky Survey, then targeted follow-ups from various other asteroid observers. The object's evident extrasolar origin ...

3

You might take a look at this 2006 paper by Thomas et al. on centroiding algorithms for astronomical adaptive-optics (AO) systems, which includes a detailed discussion of error estimates for the centroid position using different algorithms. The approach you describe in your answer corresponds to what they call "simple centroid" (Section 3); they refer to a ...

3

Your vantage point changes throughout the year as the Earth moves around the solar-system barycentre (close to the centre of the Sun). That means the positions of nearby stars "wiggle" with respect to more distant background stars, with a period of one year; the amplitude of this wiggle is how you determine the parallax distance to the object. In the case ...

3

Short Answer They're the same. Long Answer Local Standard of Rest (LSR) Let me start out by defining the dynamical Local Standard of Rest (dynamical LSR or also LSRD). This definition is taken straight from An Introduction to Modern Astrophysics, 2nd Ed. by Carrol & Ostlie, page 903 (emphasis theirs). To investigate the motion of the Sun and other stars ...

3

The early 1990s Hipparcos mission yielded parallaxes for 118000 stars (Hipparcos catalog) and positions without parallax for another 2.4 million (Tycho-2 catalog). The Tycho-Gaia astrometric solution (TGAS) combines those data with preliminary Gaia observations to get 2 million parallaxes, "only" 17 times as many as Hipparcos, with better precision. If this ...

3

Exoplanets is an almost over populated field of research now, so yes they are monitored. But maybe not too much beyond what is needed to confirm their existence. I think you have to humble yourself in the enormity of time. There are some transient events in astronomy, but mostly, watching the sky is like watching a rock. Nothing much changes. Phoebes is ...

3

In the opposite direction (RA= 07h 25m 31s ± 10s, +26° 57′ ± 20′, J2000.0, seen from Earth) of the positive horn of the Wow!-signal (RA= 19h 25m 31s ± 10s, −26° 57′ ± 20′, in J2000.0 coordinates), Iota Geminorum, aka Propus, (RA= 07h 25m 43.6s, +27° 47' 53") is within a 3-sigma error ellipse (1.26 sigma in RA, 2.54 sigma in Dec, 2.84 sigma total error). ...

3

Parallax and proper motion are determined from a series of position measurements taken over the course of (for Gaia DR2) 22 months. A "5-parameter" astrometric model is fitted to these position measurements, consisting of a sky position at some epoch, a parallax and a proper motion in each of the celestial coordinates. The precisions of each of these ...

2

After installation set up,the coordinates Ra and Dec are locked in to the ra of GMT(0 astronomically) and installation latitude.These are input requirements of installation. From that point,an onboard clock remembers all points from that reference. It is not a sat-nav base unit and installation would have to be repeated if repositioned in another location.

2

Assuming that each (square) pixel has the same angular scale (not a given if the field of view is large) of $\theta$ degrees/pixel. Then the declination (in degrees): $\delta \simeq \delta_0 + \theta y$ The right ascension (in degrees): $\alpha \simeq \alpha_0 - \theta x/\cos \delta$ where $\alpha_0$ and $\delta_0$ are the RA and Dec at $x=0$, $y=0$. [...

2

The DE430 JPL ephemeris "memo" (https://ipnpr.jpl.nasa.gov/progress_report/42-196/196C.pdf) has details of how it is constructed and what from. Mercury and Venus's positions are tracked by tracking the spacecraft orbiting them (to sub-km accuracy). Mars, Jupiter and Saturn are also measured from the orbiting spacecraft such as Galileo and Cassini. The outer ...

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