robin_astro

The universe does not care about my view of our origins (and neither should you as you have no idea who I am, what my views on the subject are or if I have any knowledge of the subject) The same is true of our youtuber though so I made a point of following up the source publications, which should be included in any scientific presentation. The story often turns out, as here to be very different but equally interesting. For example the actual story behind the spurious mars seismometer signal (caused by a small thermally induced deformation in the top <1mm thick layer of the Martian surface) is that it could perhaps be used to improve the accuracy of our predictions of the orbit of Phobos which is important for future missions. Who would have though it !

Yes let's do this where we can read what the professional scientists actually found rather than following these clickbait headlines https://www.frontiersin.org/articles/10.3389/fmicb.2020.02050/full https://ethz.ch/en/news-and-events/eth-news/news/2020/09/surprise-on-mars.html ie the experiment did not "prove panspermia" and nothing "strange happens on mars during an eclipse"

"....survived for 3 years... proof of panspermia And this week's award for sensationalist extrapolation goes to... ! Without the original references these sort of presentations are useless. I highly doubt that the scientists involved made the claims he is promoting here in either of these presentations EDIT 2020-10-15: the quote "....survived for 3 years... proof of panspermia" was a direct quote from the headline on the embedded video at the time I posted my reply. This has been changed several times by the youtuber since then, possibly as a result of my comments, I don't know. It is a good example of why nobody should embed content from a website they do not control or trust 100% or comment on posts containing embedded content since this can be changed without any indication it has been edited

The emission is caused by resonant scattering of sunlight off sodium atoms when in direct sunlight. With the sun above (or just below) the horizon, the bright sunlight (scattered off lower levels of the atmosphere) dominates the sky spectrum so the sodium D lines appear in absorption. After the sun sets as seen from the ground, the higher layers of the atmosphere are still illuminated by the sun so we see the emission from the sodium atoms. Cheers Robin

Not a book but I find Michael Richmond's lecture notes good as they link observations and astrophysics in a concise but rigorous way. This one is relevant here http://spiff.rit.edu/classes/phys230/phys230.html particularly 12, 16-23 Cheers Robin

Hypernovae are thought to be particularly energetic supernovae formed by core collapse of massive stars so yes, potentially producing a black hole if the remaining core is massive enough to form a black hole rather than a neutron star (Note that it is suspected that not all stars that collapse into a black holes necessarily produce a supernova explosions though. I believe this is an area of study) The spectrum of hypernovae show them to be type Ic, similar to type II but the original star had lost all its hydrogen before the explosion (hydrogen is not seen in the spectrum). The lines in hypernovae spectra are much broader though because of the high velocity of the explosion so are characterised as type Ic BL. Here is an example of supernova which I classified as a type Ic BL. I don't know if it was powerful enough to count as a hypernova though. https://wis-tns.weizmann.ac.il/object/2017ixv Someone has kindly listed the known details of galactic supernova remnants here. Most are of unidentified type but there are some type Ic and some possible black holes. Not sure if any are hypernovae though https://en.wikipedia.org/wiki/List_of_supernova_remnants This article does identify a possible extra galactic hypernova remnant though in M101 https://imagine.gsfc.nasa.gov/news/20may99.html (Treat the explanation with caution though - it is over 20 years ago) Robin

Your question prompted me to go in search of the Veil supernova pulsar (In the literature, not the sky !) I turned up this possible candidate "DISCOVERY OF A PULSAR WIND NEBULA CANDIDATE IN THE CYGNUS LOOP" https://iopscience.iop.org/article/10.1088/2041-8205/754/1/L7/meta Robin

Hi Marv, This NASA reference suggests the progenitor for the Veil was a 20 solar mass star so a type II supernova which ran out of fuel and collapsed, the released gravitational energy powering the explosion. Most of the material would have been thrown out to produce the nebula, though there should be a neutron star left behind somewhere (A pulsar, the rapidly rotating, slowly cooling dense core of the star) https://www.nasa.gov/image-feature/veil-nebula-supernova-remnant The crab nebula is an other recent example of a type II supernova (Note type Ia supernovae also produce remnant nebulae but don't leave a star behind as the white dwarf is completely destroyed in the thermonuclear explosion) Cheers Robin

Ha-Ha yes it does look silly 🙂 It is a "filly dot" decorative gas discharge lamp from Habitat, famous among amateur spectroscopists looking for calibration sources http://astrosurf.com/buil/calibration/lamp1.htm I don't often use it now as the spectrographs now have internal lamps (Richard Walker discovered that fluorescent lamp starters also worked so could be built into spectrographs, more amateur resourcefulness ! ) It is still useful for superimposing lines directly on the measured spectrum for very high precision wavelength calibration though as here for example (at 18min 35 sec) https://britastro.org/video/13862/14769

There is still some around showing at high resolution in this raw image from last night under poor conditions (LHIRES 1200 l/mm R~11500) but significantly less than 10 days ago when the comet was closer to the sun Note how the displacement between the comet and sky emission lines due to the Doppler effect has reduced as the comet is moving slower in our direction relative to us now Cheers Robin

This was with the ALPY 600 on the Celestron C11 (same as here but the science camera is now an ATIK 428) The ATK 314 there is now used on the LHIRES III so I can swap the instruments over complete with cameras in a few minutes

Here is an emission line spectrum taken from the tail of C2020 F3 (NEOWISE), compared with that of the inner coma. It was taken with an ALPY600 and the intensity in the spectrum is only ~1% of that in the coma. It is very different from the spectrum of the coma that you usually see. The C2 Swan bands are absent and are replaced by a series of double lines from CO+ which give the ion tail its blue colour Cheers Robin

Hi Jim The resolution of the LHIRES with a 2400 l/mm grating is about 4x higher than the LowSpec with a 1200 l/mm grating. (~0.5A compared with 2A. An 1800l/mm grating would be better). You would be able to detect Doppler shifts of this magnitude (It is relatively straightforward to detect shifts of say ~1/20 of the resolution) but the shifts would be less than the resolution so not resolved like in this example. Cheers Robin

I have now processed and calibrated the high resolution spectrum. See the attached poster. The Sodium emission dominates the spectrum. (There is as much light from the two narrow sodium lines as in the rest of the light in the spectrum combined.) There are no other strong lines in this yellow part of the spectrum (the Swan Bands are further to the blue-green) There are some other faint emission lines though which I have not yet been able to identify We can measure Doppler shifts to calculate the comet's motion both relative to us and to the Sun using the sodium light pollution and daylight spectrum as references The Doppler shift in the sodium emission lines gives the velocity relative to us directly = -55 km/s (ie the comet is moving towards us) We see the Sun's absorption line spectrum in the sunlight scattered from the comet dust. These absorption lines experience two Doppler shifts, first due to the motion relative to the Sun and then after scattering due to the motion relative to us. This total shift = -23km/s The motion of the comet relative to the sun is therefore -23 +55 = +32 km/s (ie the comet is moving away from the Sun) These results are pleasingly close to the figures given by the JPL Horizons website for the time of the observation (-54.9km/s and 31.4 km/s) https://ssd.jpl.nasa.gov/horizons.cgi Robin

From NEOWISE observations the nucleus is ~5 km diameter apparently which is on the large size according to the S&T website https://skyandtelescope.org/astronomy-news/comet-neowise-delights-at-dawn/ but we don't see the nucleus as it is completely shrouded in dust Robin

A quick back of envelope calculation off the image gives ~60km/s towards us. (A note for all doom mongers and conspiracy theorists who might be lurking - This does not mean it is going to hit us, it is also moving sideways relative to us !) The shift is ~6 pixels and the spacing between the two Na D lines (6A) is ~32 pixels so 6* 6/32 ~ 1.125 Angstrom blue shift. The Na D doublet wavelength is 5893 A so velocity = c * 1.125/5893 = 57km/s It will be interesting to see if the velocity relative to the sun can also be picked from the shift in the solar absorption lines from the scattered sunlight (a combination of both the velocity relative to the sun and us.) Cheers Robin

Now visible from the observatory. This is what the raw spectrum image looked like lat night in the region around the Sodium D lines at ~0.4A resolution (LHIRESIII slit spectrograph with a 2400l/mm grating covering ~150 A). The inset image is from the guide camera to show the position of the slit. I have over exposed the coma in this image to bring out the detail in the spectrum of the tail. The sodium emission is very intense but there is also some weaker molecular emission lines present. (To be identified once I have wavelength calibrated using the spectrograph internal Ne/Ar lamp). Note the blue Doppler shift in the Na D emission lines relative to lines in the sky background due to the comet's motion. Cheers Robin

The Comet 2020 F3 NEOWISE should make a great target for high resolution spectroscopy once it becomes visible from my observatory in a few days but I tried it a couple of days ago with a simple portable rig consisting of the Star Analyser 100 in front of 50mm SLR lens mounted on an ASI120MM, normally used as a guide camera on the observatory spectrographs There is little contrast between the spectrum and the bright sky but the Sodium emission is obvious as a tiny image of the comet in the spectrum. This is quite unusual I think, the first comet I have measured showing this. As a bit of fun I followed in the footsteps of Bundsen and Kirchoff and took a spectrum of sodium (salt in a flame) using the same setupand and compared them, proving it really was sodium !

The direct link to the series of articles (in English) is here https://astropeiler.de/beobachtungen-der-21-cm-linie-mit-einfachen-mitteln Robin

You could build a "Micro Arecibo" using your satellite dish (fig 14 of the pdf) 🙂

I was surprised to find that given a decent receiver lineup the Milky Way Hydrogen line is detectable with some remarkably simple antennae (eg even a dipole plus a CD as a reflector !) https://astropeiler.de/sites/default/files/Hydrogen_4.pdf From this website https://astropeiler.de/

ALPY is fixed resolution at ~12 Angstrom. (Except for my modified supernova classifier version 🙂 ) . You can vary the dispersion/resolution of the Lowspec by changing gratings and slit width. There is a lot more to a spectrograph than this though. For example the ALPY is designed to operate down to f4 whereas the Lowspec has severe chromatism at low f ratios due to the simpler off the shelf optics which means the spectrum goes out of focus at the blue and red end. To avoid this you need to run a higher focal ratio which means a wider slit and a higher dispersion for the same resolution. The ALPY is also extremely stable both with regards to temperature and flexure and so once set can be run without any intervention, good for remote operation. Of course you also need to produce the parts and assemble them with the Lowspec. (A commercially produced Lowspec would likely be more expensive than the ALPY, similar to what happened with the LHIRES which was originally a not for profit kit ) Theclosest commerical comparison with the Lowspec is probably the Shelyak LHIRES or Baader DADOS Cheers Robin

The manuals which go with the Star Analyser and ALPY also have some useful general information on how to record and process spectra https://www.patonhawksley.com/resources https://www.shelyak.com/produit/alpy-600/?lang=en

Also the spectroscopy resources page on the BAA website https://britastro.org/node/19378 For example my NLO workshop presentations which cover producing spectra using both the simple slitless Star Analyser grating and an ALPY 600 slit spectrograph https://www.britastro.org/downloads/15701

Yes. The larger the aperture the more photons you collect in a given time. (You might decide to spread them over the detector to a different extent eg by choosing the focal ratio but that is independent of aperture). The more photons you collect the more you know about the object as I demonstrated up the thread so the larger the aperture and the longer you "stare" at it, the more information about the object you acquire. In a perfect system (no noise, no distortion of the signal between the object and you) :- The first photon tells you there is an object emitting light the second photon (or more accurately, the time between them and the difference in direction) tells you a little bit more about the object (A hint towards deciding if it is a point or an extended source and very, very roughly its brightness) The third and subsequent photons increases the precision of the brightness estimate and if it is an extended object adds information about the size, structure and brightness variation across it. Each subsequent photon adds more detail in the way I described. Different equipment may have different abilities to distinguish which direction they are coming from (spacial resolution) but at the end of the day the more photons, the more accurate description of the object you get Robin