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My apologies. One of Uranus and two of Neptune. That’s what comes of relying on memory rather than re-checking sources.
My suggestion remains unchanged.
It will have to wait for a few days. The moon is so bright tonight that the sky is very obviously blue and I still have vestigial colour vision in the red-orange-yellow part of the spectrum.
Blue sky at night, astronomers take fright.
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.
Hi Joan,
Your first call should be the ARPS home page, https://britastro.org/sections/asteroids where you will find the director of the section is Richard Miles. Contacting him would be a very good idea.
Wayne Hawley is coordinating the observations of several asteroids with the intent of deriving rotational periods. In particular, we are concentrating on 703 Noemi this week as that portion of its phase curve is not well determined.
Rather than give their email addresses here, please send me email directly and I will send them to you. You know where I am!
Paul (J22)
According to Jonathan McDowell (@planet4589 on Xitter):
The Chang Zheng 6 upper stage from the 2021 Apr 27 launch reentered over Hawaii on Feb 9 around 0949 UTC.
The oscillator strengths reflect the fact that transitions are more likely between quantum mechanical states with similar wavefunctions – which give rise to strong lines – versus those with very dissimilar wavefunctions – which give rise to weak “forbidden” lines. But calculating wavefunctions is somewhere between difficult and impossible, and numerical approximation often don’t seem to resemble reality particularly well. Hence the tendency to use empirical lab measurements.
This is bringing back memories.
I am but a humble experimental chemist and know rather little quantitative about atomic spectroscopy, other than hydrogenic systems in the Schrödinger approximation. My DPhil research, was on robvibronic structure in the electronic spectra of Cu2 and CeO in the gas phase. More recently I helped the Exomol team with AlH. A beauty of that field of work is there is a plethora of rotational lines, by and large, and frequently a good number of vibrational bands. Fairly easy to measure the temperature also. With all those measurements fitting a potential curve is not entirely trivial, especially near dissociation, and very difficult when two states perturb each other. However, very accurate results are possible and it is (usually) straightforward to reverse engineer properties such as dipole moment, polarizability and so on. In particular, oscillator strengths — which is what this thread has done to refresh my RAM.
Thank you both.
(BTW, One state in AlH is barely bound and I failed to get a good enough approximatiom to the potential energy curve. Believe it or not, an ab initio calculation was the key to solving this one. It gave a fairly good PEC but a not particularly good absolute energy. The latter was known very precisely from the spectra and putting the two together gave excellent predictions for the oscillator strengths.)
Robin: true.
I question whether it is cheaper to put large structures in space or whether to put large structures (such as transmission lines) on the ground at a range of longitudes.
Or, for that matter, to install storage mechanisms to convert daylight solar energy into nighttime electricity. Batteries, in the general sense of the word, are relatively cheap. Raising a cubic kilometer of mass a hundred metres stores a lot of energy and uses technology which has been well understood and implemented for a hundred years. Melting and re-solidifying a phase-change material, such as NaCl, likewise.
Not obviously cost effective. It’s much cheaper to double the collecting area on the ground than to do so in space.
I’ve seen some where the entire image dynamic range is in the range of 0.0 to 1.0 and that clearly doesn’t work very well if you just truncate.
That is relatively sane compared with some formats I have seen. SWarp, in particular, can generate values which are negative and in a range which bears little resemblance to that of 16-bit signed integers. The result is fully compliant with the FITS standard and, for example, ds9 has no trouble dealing with such images.
That’s why I had to write my own conversion routine.
Ah, the beauty of standards!
It is very important, IMAO, to have a standard. So important that everyone should have one of their own.
Are the files roughly the same size? The raw files you get from the camera are probably 16-bit integer (BITPIX=16). After calibration they may be floating point (BITPIX=-32) and it may be that Vphot can’t cope with that. The FP files will be twice the size of the integer ones. If Vphot can’t cope with FP that is a bit poor but there may be an option in ASTAP to save as ints.
I hit exactly that problem with Astrometrica. To solve it I wrote a Perl script to convert from floating point back to 16-bit unsigned integers. Not entirely trivial because a FP number can be negative and the range can be greater than supported in 16 bits, so off-setting and scaling was required.
David: I am supposed to know what “oscillator strength” means in the context of time dependent quantum mechanics but my memory has rotted in the last 40 years or so and can no longer describe it particularly coherently. Time I ran a refresh cycle on my RAM.
Mark me as recently mystified.
Beside which, I will not be Astrofesting this year.
The FITS standard defines a format for metadata headers and mandates some of them.
Within reason, you can put pretty much anything in there. Whether a particular FITS-reading program interprets them in an intended manner is an entirely different matter.
For instance, whether either, neither, or both of “EXPOSURE” or “EXPTIME” is present depends on the writing program. My code to read FITS files has to be able to handle both and to work out what to do if their values differ.
Everyone else would need ear protection if I were to join in.
Only dogs like my singing; they howl along with me.
Grant, quick question: why do you want a monochrome camera on this kit?
I can answer why I might find one attractive: I like doing photometry in standard wavebands and also like capturing every possible photon for faint object detection and/or astrometry. I am not very interested in taking pretty picture.
Paul
I can take a look. I have SR, SI and TR filters available. SR has 90% transmission at H-alpha so perhaps that may be the best bet. I also have only 4% of the collecting area of the Hale but, there again, so does WISE.
No promises of seeing anything by myself, in other words, but perhaps any data I do take can be stacked with those of others.
Now that I am back in La Palma and have access to my observatory I can check the log book.
It appears that useful observations were made on 43 nights. More were undoubtedly clear, at least in part and some quite probably after I had given up waiting for the clouds to clear earlier in the night.
Bear in mind that I live in LP for less than half the year. In 2023 only 141 days were spent here and six of those were spent traveling.
As one might expect the evening I arrived here, 2024-01-11, was clear but I was exhausted after a trip which began at 02:00 that morning. The sky has been cloudy ever since.
David: please don’t recycle them. I would be happy to collect but I am off to La Palma in a couple of days, returning Easter-ish, so can’t do anything any time soon. If others want them, please give them priority.
BTW, I have a bunch of BAA Handbook back issues which are free to a good home. They are duplicates of my main collection which is essentially complete back to the 1940s. If anyone may be able to fill gaps, please let me know.
Paul
