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If you haven’t seen it yet there is an amazing “selfie” of JWST’s primary mirror on the JWST blog taken using the pupil imaging lens in NIRCam.
Isn’t the web wonderful? I like this statement at the top of that page: “Once the book has been published (anticipated publication date May 2005), the download option will be disabled, so authors should take advantage of the opportunity to download their chapters now”.
That’s a very interesting observation.
There is an entire chapter on this in Comets II (edited by Festou, Keller and Weaver) which describes the generation and distribution of species in the coma (pp 425 onwards). It was published in 2004 before much of the recent space-based observations of comets but it is an excellent reference book if you can get hold of a copy. I can see some second-hand around £60 online. The book is so massive that it is in imminent danger of collapsing under its own gravity. A more recent book, “An introduction to comets” by Nicolas Thomas is post-Rosetta and also covers this.
I run my RMS cameras at 1920×1080, the normal configuration is 1280×720. This increases the file size a bit. I also use ffmpeg at a higher quality level.
This one is drifting slowly in alt/az downwards and to the right. It is NORAD 21893 (Superbird B1) which was launched in 1992 and which is long defunct. It is in a highly inclined (14 deg) graveyard orbit. Uncontrolled GEOs are perturbed by lunar and solar gravity and their inclination drifts away from 0 deg.
It is almost stationary in alt/az so must be near GEO. Candidates are Eutelsat W2, Telstar 6 and Meteosat 8. All three are drifting slowly slightly above GEO in the graveyard.
As of Feb 3 the telescope is pointing at HD 84406 in UMa. This should mean that we can calculate the aspect angle of the sunshield and the effect this has on the apparent magnitude as seen from the Earth. It might explain why the telescope was so much brighter last night. The optical collimation has now begun and the blog has a fascinating description of how it will be done. It is well worth a read.
JWST has been mag 13.0 from around Feb 4.85 to Feb 5.01 tonight, pretty bright for an object at L2. The Ariane upper stage, which is now 2.5 million km away, was around 20.2 at Feb 4.95.
That is an impressive mangling of two perfectly good facts (you can image the spacecraft with a telescope from Earth and the first calibration star is a binocular object in UMa) to produce a typically silly Daily Mail science story. Thanks both for giving me a chuckle over breakfast.
John – That is a really useful document and it would be great to get it uploaded as an HTML page somewhere that is easy to find on the website. Hopefully you can get the circulars uploaded too. Once they get indexed they will be easy to search and that would be a great resource. I know that a new website design is on the way and it would be nice to see a dedicated BAA archives section on that.
I’ve been gradually scanning Comet Section material and some of that is here.
It was cloudy here in Chelmsford but I was a long way to the east of the track in any case. The 55km eastward shift is almost at the prediction’s 3-sigma error so that seems quite significant.
Sheridan, I wonder where these other items, particularly the circulars, ended up. They would certainly be very useful if they were online and searchable. Do you still have copies?
I’m not aware of one but it would certainly be nice to have. My first paper circular is No. 557, dated 1974 October 16. It announced the discovery of Nova Sgr which became V3888 Sgr I think. They were a slightly odd paper size (not quite A5) in those days but would probably be something that could be scanned quite quickly.
I’ll be talking about JWST at the meeting tomorrow. If you have any recent observations please let me know by tonight. I got some astrometry of the Ariane upper stage a couple of nights ago and it is now around magnitude 19. The observatory was mag 16. Everything seems to be going very well with the mission so far.
There’s at least one thing in the descriptive Bortle list that I think sounds very wrong. Bortle 7 (the suburban/urban transition) is probably where I am in Chelmsford most nights but the description says “when it is full moon in a dark location the sky appears like this, but with the difference that the sky appears blue”. This must be rubbish surely? My image processing pipeline produces an estimate of the sky brightness for each image. On a good, dark, transparent night from here I get around 19.2 mag/arcsec^2 near the zenith. A couple of nights ago at full moon I got 16.5 mag/arcsec^2 at the zenith. That sky brightness would be the same even in a normally very dark place since it dominates scattered artificial light so to suggest that my “dark” skies are the same as full moon skies in the countryside seems a bit daft.
Phil – That is a really interesting observation.
I assume at the moment the spacecraft attitude will be quite stable. I don’t know whether the solar array can be steered to some extent relative to the bus but for now I would guess that they are keeping the spacecraft sun-pointing although I don’t know that for sure. If that is so then the brightness variations will be due to the phase angle (i.e. sun, spacecraft, observer). The repeatability here implies a diurnal variation. At the current range (about 1.2 million km) the Earth has an apparent diameter of 0.6 degrees so the effect of parallax on the phase angle is very small although certainly large enough to affect the timing of specular glints depending on where you are.
It would be very interesting to get two observers separated by a long baseline to do photometry at the same time. I suspect that they would see quite different profiles.
Once JWST goes operational the spacecraft attitude will be continually changing depending on the target so these glints will become much more (apparently) random.
I know some people are still attempting to image both objects. The ephemerides available from Project Pluto are still good but the magnitude of the upper stage was quite faint last time I imaged it on Jan 12.9. It is around mag 19 at the moment. The magnitude of JWST is highly variable depending on the precise orientation of the spacecraft.
The entire deployment sequence seems to have gone without a hitch with both folding sides of the primary mirror now locked in place. That is pretty amazing given the complexity.
That’s a really nice observation. If you look at images of JWST you can see that we are mainly seeing the 21x14m sunshield but there is other stuff on the sunward side of the spacecraft including the solar panel and the spacecraft bus and propulsion units. Some sunlight will be scattered back to us from these other components but there will be strong glints from the sunshield which will be highly dependent on the relative angle between the sun and the observer. Given JWST’s configuration even small changes in this angle will make a significant change to the magnitude we see.
When the telescope is operating at L2 it is in a large radius halo orbit and the attitude will change for each observation since the telescope and sunshade are fixed to each other. It will be an interesting project to try to predict when glints would occur given the target list that the telescope will be aimed at.
