Uranus – Stop Snickering

Stack of 10 images 800 iso 45 seconds 200mm f/4 cropped to about 1/3

The image is not inspiring and, at magnitude 5.7 Uranus is not a tough target but i’m pleased for a number of reasons:

  • It’s Uranus for pete’s sake, 3 billion kilometers away
  • I found it in the image by using the WCS file that astrometry.net produces
  • I learned about relating my images to stellarium’s displays
  • There are a bunch of faint stars that i can get my eye in on

I routinely do image recognition by uploading to astrometry.net. Besides the annotated image as below, it provides a WCS.fits file that provides the info you need to map from astronomical coordinates (RA and Dec) to pixel locations in the image. The python script below reads the WCS file and uses astropy to determine the pixel location for uranus.

from astropy import wcs
from astropy.io.fits import getheader
import numpy as np
from astropy.io import fits
from astropy import units as u
from astropy.coordinates import SkyCoord as SC

hdulist = fits.open(r"c:\users\bill\downloads\wcsuranus.fits")
w = wcs.WCS(hdulist[0].header)

pixcrd = np.array([[0, 0]], dtype=np.float64)
world = w.wcs_pix2world(pixcrd, 0)
print("RA/DEC for [0,0]: ",world)

wcrd=np.array([[36.542, 14.101]])
print("Pixel Coords for center as given by astrometry: ",pixcrd2)

uc=SC('2h27m45.84s', '14d6m14.0s')
print("Uranus's Coordinates(J2000): ",uc)
print("Uranus's Pixel Coordinates: ",uc.to_pixel(w))

I finally realize that i can line up my images with the stellarium displays if i put stellarium into equatorial mount mode and rotate it’s image right 90 degrees. I still find this a bit confusing but the equatorial mode is key.

Oh, also, I think the faintest stars I can reliably pick out are around magnitude 11-12 so i’m a long way from pluto’s 15.


A Tiny Perfect Ring Nebula

I’m delighted with this image of M57, the ring nebula in Lyra. I wasn’t sure I could see it at all, it’s very small compared to the galaxy targets I’ve been shooting. The ring is only about 15 pixels across in the final image but it seems perfectly clear to me. This is 11 lights at 25 sec ISO 800 shot through the Takumar 200mm lens wide open at f/4 combined with darks and biases, no flats. Processed in Siril then cropped to about 1/10 of the original. After Siril I used Paint Shop Pro and reduced brightness -15 and boosted contrast +26.

Wikipedia gives the dimensions as 230″X230″ (arcseconds) so about 4’X4′ (arcminutes) I think my camera/lens is supposed to be 2.2 arcsec/pixel so that would be only 10 px where my image is about 15px. Maybe bad focus or CA fuzziness are helping me out for a change! Jupiter at opposition is only about 50″.

UPDATE: My images are about 4.4 arcsec/pixel so 15px is 66 arcsec. NASA gives the size as 1.3 arcmin so i’m missing the red part – that’s fine.

The actual object M57 is about 2500 light years away and almost a light year across. which is around the 1.3 arcmin NASA gives.

For processing I am trying to centralize my calibration images – darks, biases, flats – and use symlinks to make Siril think they’re in the directory with the lights.

On Jupiter’s Moons

This is a random setup shot through the 200mm lens where I was using jupiter to set my aim. It’s 1 second f/4 ISO 6400. It amuses me that Jupiter’s moons show so well. If you look at the inset you can see io, Ganymede, and Callisto. I checked against stellarium and they are the right distance from the planet – Callisto being 6′(arc minutes) which translates to 80-odd pixels in the image. The moons are all around magnitude 5 which makes them naked eye visible but I guess without a telescope they’d be lost in Jupiter’s brightness.

Pluto – But Not Yet

I was out last night to look for the comet – i didn’t have my mount but i did have the camera and tripod and it was a nice night so i took a shot near jupiter where i know pluto is hiding. I would say good prospects. The area is fairly dark and there are good guide stars. On the right is a shot from stellarium with pluto selected. On the left is the framing shot with the takumar 200mm lens wide open 2.5 seconds ISO 6400. The dimmest stars I can see are probably mag 9-10 which is a long way from pluto’s 14.9 but i’d like to think that i’ll get close by stacking and it will be good practice for neptune, ceres and vesta later in the year.

Target Pluto

Pluto is impossibly far away and wee – it’s like 3 billion miles away and smaller than the earth’s moon. However, it’s easy to find right now – within a degree or so of Jupiter. It is nominally magnitude 14 and, with luck, I my be able to pick up an impression of it later in the summer. I know that I have picked up stars that dim with the 200mm takumar.

In the image above the red outline is the field of view with my that lens.

In the image below, I have seen this magnitude 14.81 star in M101 shots so maybe…

M101 AgainAgain

This is over-processed but I kind of like it. This is 60+ exposures through the Takumar 200mm lens at about f/5.6. Each exposure was 60 seconds at ISO 1600. I had only 3 darks and 9 bias shots and no flats. I used SiriL for the processing following this tutorial. After Siril I used Paintshop Pro 5 to boost the contrast quite a bit further further – (Colors/Brightness/contrast=59 with no added brightness).

This is about 25% of the full image. I don’t care too much about anything outside the central image but i do note really bad vignetting on the full shot as shown below. I’m going to take some flats to see if they help.

I also note that my stars are not great – a little stretching top to bottom. I had what i consider excellent alignment – within two arcminutes. I may not have been perfectly level but i was close.


Starlink 1270 and 1229

This is a faint and janky image of M101. I would normally have tossed it but i noticed two faint scratches running diagonally off to the right of the faint fuzzy. These are two of the Starlink satellites – the first ones i’ve actually seen although heavens above is full of them. The image was taken through the takumar 200mm lens at f/5.6 120 seconds at ISO 800.

Repeating Galaxy Hunting M101

This is not awful at all! Nine out of 14 exposures 90 seconds, ISO 800, f/5.6 with the Takumar 200mm lens on the canon t3i. The spiral of the pinwheel nebula is faint but clear. and you can see the faint fuzzy of NGC 5474 below and to the right. In fact, aided by Astrometry.net and the eye of faith I can see at least NGC 5473 below M101 and left, NGC 5485 still lower and left and NGC 5422 above and left of M101.

I used DeepSky Stacker per this tutorial which is clear and specific. I had taken more images earlier in the month and stacked them then with less success.


From my back yard I have good views to the high north, east, and overhead. M13 – the great cluster in Hercules was ideally positioned last night with no moon but the seeing was fairly crappy. I was really just out to try sharpcap polar alignment but i took a couple of quick snaps.

This is one shot to JPG 60 seconds ISO 400 about f/5.6 through the Takumar 200mm lens. I’m pretty pleased.