M45 by daylight.

Forums General Discussion M45 by daylight.

Viewing 5 posts - 1 through 5 (of 5 total)
  • Author
  • #621771
    Dr Paul Leyland

    This is just a bit of light-hearted idiocy, so please don’t take it too seriously.

    On Xitter today I saw that the Moon lies close to the Pleiades at the moment. My telescope doesn’t have absolute positioning but I can see the Moon through the finder and I can determine its position with MaximDL. Why not, I thought …

    A quick snapshot (only 0.05s) through a Sloan i’ filter (to darken the sky as best I can) showed craters very nicely. Syncing the mount with the lunar position told the telescope where it was pointing to within 10 arcmin or so. I then slewed to Alcyone, and saw nothing. The field of view is only about 13 arcmin so it was not too surprising that no stars were visible.

    Lots of slewing around pretty much at random produced a number of images which show stars. Unfortunately I have not yet been able to identify any of them but I am sure that they are members of Messier 45. Local solar time was between 13:30 and 14:00.

    Encouraged by this success I may try to do a better job some time. It will require cleaner optics and a less hazy sky, presumably. The sky isn’t bad today but I have certainly seen it better. Another possibility might be to use the Moon, Jupiter or Venus (all of which are readily visible through the finder) for an initial position and then search for something as bright as Sirius or Rigel or Betelgeuse to refine the mount’s co-ordinates. A few half-hearted attempts at image processing also made the stellar images more readily visible.

    If any more progress is made, I may try for other bright Messier objects by daylight. Only star clusters may be feasible, I guess. If anyone else would like to have a go, please report your success or lack thereof.

    Robin Leadbeater

    Stars with H alpha emission lines (of which there are several in the Pleiades) in a narrow band H alpha filter (where the solar spectrum has a deep absorption) might be interesting.

    Dr Paul Leyland

    Robin: indeed an interesting proposal. I don’t have such a filter but others doubtless do. They are hereby challenged to try it!

    I also thought of using a video camera, subtracting a constant level from each frame (the minimum value contained in the frame might work) and then co-adding a goodly number of frames. Again, a constant level would be removed from the final stack.

    The sky, being a noisy constant, would be smoothed and reduced markedly but the (again noisy) signal from the stars would be increased relative to the background.

    This, of course, is essentially what I do to image extragalactic GCs, TNOs, and satellites in the outer solar system, some of which are markedly fainter than the sky behind them, though rarely are more than a couple of hundred subs stacked.

    Dr Paul Leyland

    I have now done a little more analysis of the images taken on 2024-02-16 and believe that I have identified three stars in M45.

    The first step was to co-add all the images which did not show any stars and use the result as a flat field. Not having taken any true flats with the i’ filter this was the best I could do. It actually worked extremely well when applied to the images which did contain stars.

    It was quite impossible to put a WCS on the images so I examined each for distinctive objects which may be found by comparing with the DSS2 survey. I knew the image scale (0.6 arcsec/pix) and approximate camera angle (-177 degrees) so when a double star was found on image number 47, I could tell that the centroids were calculated as 9.5arcsec apart and at a PA of 225 degrees, the primary being markedly brighter than the secondary. Wandering around the Pleiades I came across HD23964A and HD23964C in SIMBAD and cross-referenced with the Washington Double Star catalog where their separation is given as 10.4arcsec in PA 235 degrees with magnitudes of I=6.74 for component A and (R=9.71, J=8.93) for component C. Very satisfactory!

    From that the approximate error in the RA and Dec positioning of the mount could be calculated; it came to about 1 minute in RA and -0.3 degrees in declination.

    Another bright star, slightly brighter than HD23964, was found in image number 40. Sure enough 26 Tau, at magnitude V=6.46 and J=5.68, was found well within an arcminute of the predicted position. I am reasonably confident of this identification.

    Given how easy it is to pick up 9th magnitude objects in the near infra-red with an exposure where the sky almost but not quite saturates the CCD, I think I’ll try to find some more Messier objects in daylight. Call me crazy if you wish.

    The attached images show these two objects.

    Dr Paul Leyland

    Hah! The FITS files were too big. Here they are at 50% scale and PNG format.

Viewing 5 posts - 1 through 5 (of 5 total)
  • You must be logged in to reply to this topic.