11
votes
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
8
votes
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
8
votes
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
7
votes
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
7
votes
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
5
votes
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
5
votes
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
5
votes
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
5
votes
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
4
votes
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 ...
- 41
4
votes
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
4
votes
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
3
votes
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
3
votes
Convert dates to julian day number in astropy?
The accepted string formats for date-hms are:
...
- 103k
3
votes
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
3
votes
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.
...
3
votes
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
3
votes
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
3
votes
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
3
votes
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
3
votes
Accepted
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
3
votes
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
3
votes
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
3
votes
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
3
votes
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
2
votes
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
2
votes
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
2
votes
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
2
votes
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
2
votes
Accepted
Making sense of the lomb-scargle periodogram
I think I see what is going on. Your best fit is actually a beat frequency between the true frequency (0.005) and double the sampling frequency (0.05). This does indeed produce a model that goes ...
- 131k
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