Forum Replies Created
-
Posts
-
Another thought: check this link – https://imagemagick.org/script/download.php
Completely free and, on my systems at least, thoroughly capable of conversion between almost any image format and almost any other, not to mention a vast amount of image munging abilities.
Thanks Callum.
An impressive process. 1.8 pounds of silver for each treatment! I hope they recovered the excess.
They have been named Nebucula M{aj,in}or for a very long time now.
Remember, Saturn ate his children and Jupiter has some rather controversial sexual activities in his past.
I think we decided the limiting mag was 3ish elsewhere on the sky.
I came to a similar conclusion (though perhaps half a mag fainter) when attempting to observe Venus occulting sigma Sgr some years back. The actual occultation was clouded out but 20 minutes after the star was very easily seen in a 27.5cm Maksutov Cassegrain.
It was after that episode that I became disillusioned by Asimov’s Nightfall. A superb story but the idea that their astronomers living in a globular cluster couldn’t see stars in the daytime beggars belief. Venus at its brightest is a relatively easy daylight naked eye object here on Earth and some claim to be able to see Sirius.
With a modern CMOS sensor I imagine I could do a lot better now.
Or a modern CCD for that matter. A SX 814 works beautifully down to 2ms and was used for my Pleiades imaging.
Yes, a very nice video. Stacking the frames and using something like FABADA to remove the noise and you should end up with a high SNR and, from that, estimate a plausible limiting magnitude.
FWIW, total cloud cover here right now in La Palma but at least it isn’t raining.
OK, you guys, when are you going to start imaging Messier objects? M35, M36 and M37 are well placed right now. 😉
Nick: sure.
It is easy, in my experience, to see 2nd magnitude stars through a telescope in daylight. Some decades ago Venus occulted Nunki, or sigma Sgr. From central Oxford the critical moments were clouded out but 20 minutes or so later the star was very easily visible in a 27.5cm Mak-Cas. I guess the limiting visual magnitude on that occasion was around 4 to 4.5.
What’s a summer blue daytime sky?
Anyway, interesting calculation. The wonderful book “Sunsets, twilights and evening skies” by Aden and Marjorie Meinel contains the attached plot. It indicates a factor of 70 million between a perfect night sky and the noon zenith sky. That is 2.5 * log10(70E6) = 19.6 mags. Assuming a perfect night sky to be 22 mags per square arcsec that would put the noon daytime sky at about 2.4 mags per square arcsec so a bit brighter than you calculated.
The surface brightness of the Full Moon is around 3.4 mags per arcsec so that would imply that it is about 40% the surface brightness of the daytime sky which would be easily detectable with the naked eye. That is something you should be able to demonstrate easily by taking an image and measuring it.
The cloudless sky is, of course, not white. Neither is it unpolarized. The use of a polarizing filter can make a big difference in its brightness but a more important method of darkening the sky is to observe through a red or near infrared filter.
I have already posted images of 6th and 7th magnitude Pleiads taken not too long after local noon. With my kit I estimate that I should be able to reach 12th magnitude with a Sloan i’ filter. It will be necessary to take numerous subs where the stars are almost but not quite saturated and then remove the almost as bright sky background in software.
Well, if we take Ireland as being 500 km long and the nearest Mars comes to the Earth as 60 million km then the flag would subtend around 500/60E6 = 8 microradians or about 2 arcsec so a Martian Damian Peach would definitely be able to resolve it.
Or our Martin Lewis, for that matter, who quite often produces of images showing surface details on the Galilean satellites of Jupiter, all of which are less than 2 arcsec across.
It is the dark side of the moon in the same way that Africa is the dark continent.
And, indeed, it is all dark. The albedo is comparable with fresh asphalt.
The sky over the northern hemisphere was much clearer than usual in mid-September 2001 There is little doubt that contrails have a significant effect on the amount of cloud cover.
What a nice little high-voltage supply you have built for your GM tube!
What voltage is required? I ask because I had to replace my fly-zapper recently. The blue-through-UV LEDs had died but the 4kV power supply still works fine. Perhaps it could be re-purposed.
I am also tempted to build a spark chamber. Lots of fine wires across a cube about 1m in each dimension with each wire being just higher than the breakdown voltage of undisturbed air. Such a beast shows muon tracks very nicely. Elfin safety dictates that the whole be encased in something like Perspex sheets to keep sensitive bodily parts away from the zappy things.
Hah! The FITS files were too big. Here they are at 50% scale and PNG format.
Attachments:
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.
https://www.mdpi.com/2218-1997/9/9/387 is a fascinating paper. A number of periodicities in muon flux are detectable. A strong signal with a periodicity of 125 days is found, along with a diurnal variation and one which correlates well with the temperature of the Earth’s atmosphere. The global magnetic field of the Sun influences the muon intensity and shows up as a 27 day variation.
However, another variation of about 64 days appeared at two solar maxima (but not all of them). I find this surprising!
Sorry. An OOM error. 60km/600m is a factor of 100, not 10 as given. It makes my argument even more forceful.
Muons have a rest mass of 106 MeV and are created by collisions in the Earth’s atmosphere. Their half-life is 2.2 microseconds, which is 600 metres at the speed of light. From that you can immediately deduce that any muons you detect are travelling fast enough for relativistic time dilation to be very significant. If one is created in the upper atmosphere, at 60km say, the time dilation needs to be a factor of 10. Their relativistic mass increases by the same fraction, so to create a muon in the centre of mass frame requires 1.06GeV. If an anti-muon is also created, as opposed to an anti- muon neutrino, double the energy budget. Now throw in conservation of momentum; the recoiling nucleus will also carry off a chunk of energy.
To the best of my knowledge, very few particles in the solar wind have kinetic energies of well over 1 GeV. I would be astounded if there is any noticeable variation with the solar cycle.
(All figures above rounded.)
