# Tag Info

Accepted

### Astropy units issue

In Astropy, u.G represents a Gauss, not the gravitational constant. That's why you get the "A" in one of the error messages; it represents an ampere. To ...
• 34.7k
Accepted

### What does "additive fringing from the (multiplicative) twilights" mean?

The fringing pattern is caused by thin-film interference within the CCD. The signal received in a pixel will be proportional to the light falling on it, multiplied by a sensitivity, but then some ...
• 131k
Accepted

### Right ascension - Gaia vs Simbad

1 hour = 15 degrees. 60 min = 1 hour and 60×60=3600 sec = 1hour. So to convert: (5 + 38/60 + 42.0/3600)*15 = 84.675 There is a small discrepancy, which is due to ...
• 103k
Accepted

### How do I plot galactic coordinates using matplotlib and astropy in python?

This code reads coordinates as equatorial (ra, dec) and transforms them to galactic (l, b): eq = SkyCoord(xarr[:], yarr[:], unit=u.deg) gal = eq.galactic The ...
• 17.1k
Accepted

### How can I calculate the uncertainties in magnitude like the CDS does?

That is because what is measured is a flux and the flux errors are in the DR2 catalogue. Since magnitudes are based on the logarithm of the flux, then there is no straightforward correspondence (...
• 131k

### Get orbital period of exoplanet from light curve using astropy.timeseries

The second light curve you show has no obvious periodic behaviour and I cannot see any sign of a planetary transit. The period-finding algorithm appears to be working correctly. The planet (if it ...
• 131k

### What does "additive fringing from the (multiplicative) twilights" mean?

The visual appearance of fringing is caused by the CCD (thickness) being comparable to the size of the wavelength (thin-film interference). An everyday example (same physics except with more colors) ...
• 1,081
Accepted

### How to get error out of astropy constants

While I'm not familiar with the package, a very quick look at the documentation suggests that you want In [90]: c.M_sun.uncertainty instead. I've just checked ...
• 2,787
Accepted

### L2 point ephemeris (celestial mechanics)

Bad news, this type of SPK file has a different sort of interpolation that is not supported by the jplephem package (Hermite interpolation vs Chebyshev polynomials)...
• 7,698

### Converting an RGB image to fits (astropy)

I haven't done much astronomical image processing before, but as this question is unanswered I'll give it a shot - hopefully to some avail. If the problem is more specific, a code sample/image sample ...
Accepted

### What objects can I search for using astropy.coordinates?

The astropy.coordinates packages has the SkyCoord.from_name() convenience method (docs link) uses the Sesame name resolver at ...
• 7,698

### How is CASA different from SAO DS9?

CASA is very specifically designed for analysis of data from radio telescopes and in particular interferometers, notably, ALMA and the VLA. This means it has a very large suite of radio- and ...
• 34.7k
Accepted

### Get orbital period of exoplanet from light curve using astropy.timeseries

I think you may be seeing the planet in the periodogram! But also another signal - higher harmonics of other periodic signals example - various periodic signals in our sun - with a characteristic ...
• 148

### Convert dates to julian day number in astropy?

The accepted string formats for date-hms are: ...
• 103k

### SDSS - getting separate u, g, r, i, z frames from SWARP tool and astropy

What they did was the following: for each individual filter, they assembled overlapping frames into a combined, single-filter image. E.g., they combined several g-band images into a single g-band ...
• 15.7k

### How to plot celestial equator in galactic coordinates? Why does my plot appear "backwards"?

Ok, community helped me to figure out that I faced the “mapping from the inside” issue (explained here). I'll use this answer to show my final code. ...
Accepted

### How do I plot orbit planets and satellites?

One keyword to search for is "spice kernel". SPICE stands for Spacecraft Planet Instrument C-matrix Event. That is a type of data format in which orbital data are commonly provided by ESA, ...
• 14.3k

### How can I calculate the uncertainties in magnitude like the CDS does?

For Gaia EDR3： Note (G1): Note on magnitude errors: They are obtained with a simple propagation of errors with the formulas ...
• 31

### Covariance matrix not calculated when fitting gaussians?

You must explicitly request uncertainties. fitter = fitting.LevMarLSQfitter(calc_uncertainties=True) Read the docs: https://docs.astropy.org/en/stable/api/astropy....
• 131
Accepted

### Difference in redshift between 2 interacting galaxies

From eq. 10 in Hogg's classic paper, assuming that the peculiar velocity $v_\mathrm{pec} \ll c$: $$v_\mathrm{pec} = c \frac{z_\mathrm{obs} - z_\mathrm{cos}}{1 + z_\mathrm{cos}},$$ where \$z_\mathrm{obs}...
• 35.6k
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### Are 3D coordinate data from Sloan DSS-III available & easily accessible to non-pros?

BTW if anyone wants a quick and fast query to solution do the following: Go to https://skyserver.sdss.org/dr12/en/tools/search/sql.aspx. Paste a query like this: ...
• 326

### Are 3D coordinate data from Sloan DSS-III available & easily accessible to non-pros?

SDSS DR12 Catalog Data looks like a good starting point, apparently pretty open to those willing and able to figure it out. Their SciServer Compute site hosts Jupyter notebooks to query CasJobs in SQL....
• 17.1k

### Calculating the position of stars at a given point in time

The projected separation of Mizar and Alcor is 12 arcminutes. If they are both at a distance of 25 pc (suggested by the Hipparcos satellite), then this equates to a physical separation of at least 18,...
• 131k

### Can you get motion data using astropy.coordinates.get_body()?

"Proper motion" is the name used for the motion in the sky of stars. It is not a velocity. It is not measured in metres per second, but in arcseconds per year. If a star was moving directly ...
• 103k
Accepted

### Determining when the sun shines on different sides of a building using astropy

The code below will give you the alt-az coordinates for any specified location for any specified time. From there, I think the easiest method to determine which side of the house it will hit is to ...
• 4,617

### Fitting PSF to an image to get total flux (Python)

You can't really get a PSF for an extended object. The Point-Spread-Function is a parameter of your imaging system which describes the shape of the image of a putative point source. I don't have ...
• 3,683
Accepted

### Differences between alt/az in Stellarium and Astropy

Perhaps the difference stems from the conversion algorithm? Almost certainly this is the answer. It's not clear to me exactly what Stellarium assumes for is refraction calculation, but I know ...
• 136
Accepted

### Retrieving input effective radius from Sérsic profile

The conceptual problem is that the half-light radius is the radius of a circle enclosing half the total light, assuming that the object is circular with a radial intensity profile equal to the Sersic ...
• 15.7k
Accepted

### How to query a region on the sky when given only ecliptic coordinates?

This is because the ICRS has an origin at the barycenter and this is not the same as the center of the Sun (the heliocenter). The heliocenter is offset from the barycenter (although it's still within ...
• 7,698