Amateur Astronomy


#1161

Gravitational wave event likely signaled creation of a black hole (or a nuetron star according to the paper)

phys.org/news/2018-05-gravitati … =item-menu
arxiv.org/abs/1712.03240


#1162

Still trying to get to write about cosmology but here’s a quick note about the discovery of the brightest quasar found so far. Quasars are the central black holes of galaxies that are actively feeding on matter that is falling into them. Gravitational energy is released as the matter accelerates and gets mashed into a hot accretion disc orbiting the black hole. One puzzle is that we’ve been finding huge quasars from earlier and earlier in the life of the universe, which raises issues about how they managed to grow so large in a short time.

The latest discovery is an object of superlatives. It would be invisible to the naked eye from Earth as it is forty times fainter than our nearest neighbour, Proxima Centauri. But whereas Proxima is four light years away, the new quasar is 12.5 billion! If it was brought to where Proxima is, we would be immediately zapped. Even if plonked at the centre of our galaxy it would be ten times brighter than the full moon.

The quasar is only a billion years younger than the universe. It has an incredible mass of 20 billion times the mass of our Sun. It is a quadrillion times brighter. We often measure large energy output in terms of conversion of mass to energy, according to the famous Einstein formula https://latex.codecogs.com/gif.latex?E%3Dmc^2. Our Sun will convert 10% of its mass to energy over the course of it’s ten billion year lifetime. This new quasar’s output is the equivalent of converting that amount every hour.

arxiv.org/abs/1805.04317


#1163

Life on Mars?

space.com/40792-nasa-mars-r … -2018.html


#1164

I don’t think Curiosity is capable of positively detecting life on Mars. It can do optical, X-ray and mass spectrometry, X-Ray crystallography, and gas chromatography. At most (as far as I know) the mass spectrometer could detect isotope ratios that might be suggestive of biology, i.e. different from sources of geochemical origin. Will be interesting to see what they’ve come up with though.


#1165

Oops. Correction to my earlier post:

I said that Sun would convert 10% of its mass to energy over its life. That’s wrong. It will convert 10% of its hydrogen to helium. Only 0.7% of that 10% is converted to energy (the so-called mass defect). But the statement that the new quasar puts out the same energy every hour as the Sun does in its life is still correct.


#1166

#1167

James Webb Space Telescope delayed until March 2021.
To anyone who doesn’t know, this is the successor to the Hubble Telescope.
The project has been beset with problems, resulting in a ballooning budget and numerous launch delays.
:frowning:


#1168

They now think Oumuamua is a comet rather than an asteroid. When tracking its exit from the solar system it diverged from the expected track by the width of the planet Jupiter, which they think is the result of outgassing. The lack of dust – the subject of the confusion referred to in werpen’s and my posts – is now supposed to be the result of erosion by cosmic rays over the eons.

scientificamerican.com/arti … e-a-comet/


#1169

You can see all the planets known since antiquity at the moment. Venus, Jupiter and Saturn are all visible from just after sunset. Mercury too if you’re eagle-eyed, to the lower right of Venus. Later in the night, Mars is a brilliant orange light.

Each of the planets has flirted with the moon this month too. Last week you had Jupiter just below the moon. A couple of nights ago on the 27th it was Saturn’s turn. And tomorrow night (night of 30th / wee hours of July 1st) Mars will be just four degrees below the nearly full moon. Already tonight they are a fine spectacle, making a horizontal line above the rooftops.

Needless to say it’s been perfect weather for planet spotting too.


#1170

Iridium flares are about to be no more. The Iridium satellites are in polar orbits and have three polished antennae which flare brightly but briefly (for just a few seconds) along a very specific ground track as the satellite passes overhead. Outside of the flare itself you can see the satellite body by dimly reflected light under the right conditions. If you are close to the centre of the ground track you can get down to magnitude -8, about half a dozen times brighter than Venus at its best. You can look up timings for your location at heavens-above.com.

Catch 'em while you can. SpaceX are busy launching the replacements for the whole Iridium constellation starting last January. Once they are all up sometime this year or next the older constellation will be decommissioned, and since the new ones don’t have the same polished antennae there will be no more flares.


#1171

telegraph.co.uk/science/201 … ica-holds/


#1172

telegraph.co.uk/science/201 … ica-holds/


#1173

I’ve found the reporting of this a bit patchy. Probably just the hype machine in action. This isn’t the first detection of an astrophysical source at ultrahigh energy. High energy gamma rays are detected by IACTs – Imaging Atmospheric Cherenkov Telescopes. Like the neutrino observation, they detect Cherenkov radiation, which is the electromagnetic equivalent of a sonic boom as energetic daughter particles plough through a medium. And the statement attributed in the press to one IceCube scientist that it wasn’t believed that blazars could be the source of cosmic rays is just wrong, as far as I know. The first identification of a blazar (Markarian 421) using an IACT to detect ultrahigh energy gamma rays was over 25 years ago. The gamma rays are believed to be produced by a process called inverse Compton scattering in the vicinity of the blazar’s supermassive black hole. Particles are accelerated to ultra-relativistic velocities and then scatter photons to extreme energies. The blazar can thus be the source of both high energy particles (i.e. cosmic rays) and gamma rays. It’s not all that surprising to find it producing the highest energy neutrinos too. The Reg has a decent article on it.


#1174

Google are doing a Doodle today for Georges Lemaître’s 124th birthday.

I think Lemaître is sometimes viewed a bit suspiciously as the Catholic priest who came up with a theory of creation. In fact he was a hard-nosed scientist who warned the Pope against any over-enthusiastic philosophical speculation. A few newspapers have done blurbs …

express.co.uk/news/world/98 … t-Einstein


#1175

I remember what seemed like one of the great milestone achievements of youth was figuring out how to balance a sweeping brush upside down on the palm of your hand, and to prevent it from toppling by constant small adjustments of hand position. Imagine if instead of a sweeping brush you were trying to hold up the entire contents of the universe. That was the situation in the static universe proposed by Einstein in 1917, two years after his publication of the General Theory of Relativity. He found his equations permitted the addition of a cosmological constant, representing a kind of anti-gravity that would support a changeless universe and keep it from collapsing under its own weight.

The “sweeping brush problem”, as one might call it, was pointed out by Georges Lemaître in 1927. While the static universe was possible, it required very special conditions and was hopelessly unstable under the most general assumptions. Rather than try to rescue Einstein’s universe, Lemaître pointed out that an expanding universe avoided the problem altogether. The rest, as they say, is history. Well, except it isn’t … Hubble’s discovery of the cosmic expansion in 1929 should have been Lemaître’s crowning glory, but in fact practically nobody had heard of him. His 1927 paper was published in an obscure journal that was little read outside Belgium.

In 1930 Sir Arthur Eddington, the giant of British astrophysics, wrote an English language article about Lemaître’s ideas in the Monthly Notices of the Royal Astronomical Society. I haven’t read Lemaître’s paper, but Eddington’s is available here and I was motivated to read it since Google stuck up their Lemaître doodle last week. It’s a fascinating read even if you have to skip a lot of the maths. A primary insight is that the clumping together of galaxies would cause any initially stable configuration to destabilise. It’s also interesting to note that Hubble’s measurement of the cosmic expansion the previous year was too high by a factor of seven compared to modern accepted values. This gave – to use Eddington’s words – an uncomfortably recent beginning of the universe, no more than one or two billion years ago.

Much of Eddington’s paper would not be out of place in a modern textbook but it is also interesting from a historical perspective. Sometimes science can be presented as too much of a fait accompli when in fact its development is invariably a mishmash of often mutually incompatible ideas. These grow up side by side, only for some to flourish while others wither. So recently I listened to the audio book version of Agnes Mary Clerke’s Popular History of Astronomy in the 19th Century. I can’t recommend it highly enough, although it’s not a beginner’s book and you’ll need a passing knowledge of the subject material in order to appreciate which ideas have been subsequently refined or superseded. The first edition of the book came out in 1885, but the audio book version is the 4th edition from 1902. In the short span of time between those editions, physics had made considerable leaps. The preface mentions that “Clerk Maxwell’s medium no longer figures as an indispensable factotum”, a reference to null results of experiments to detect the aether which was supposed to fill all of space.

Other major problems in astronomy were nowhere near a resolution in 1902. As an example, the processes that powered the Sun were completely unknown. Conversion of mass into energy as a result of Einstein’s Special Relativity was still some years away, but even then it was treated as a curiosity with Einstein doubting that it was a physical possibility. The detailed reactions were not worked out by Hans Bethe until 1939 and he didn’t get his Nobel prize for it until 1967!

Meanwhile, in the 19th century there were some interesting theories doing the rounds. The possibility that the Sun was actually burning like a lump of coal was considered, although calculations showed it would have difficulty persisting over geological time which was already known to be vast. Compressional heating by friction – which we now understand is how stars get started – was similarly known to have problems explaining sustained energy output. An ingenious extension of the nebular theory of star formation was conceived. The idea was that the Sun continued to accrete material to the present day, in the form of comets falling into it. Nowadays we know the rate of such accretion is much too low to sustain the Sun, but it was a reasonable guess for 19th century astronomy.

And let’s face it, there were much wackier ideas floating around. For a 19th century writer, the preeminent astronomer had to be William Herschel, the discovered of the planet Uranus. He dominated British astronomy for half a century, including the first quarter of the 19th, and his son John took up the standard thereafter. William was born only a decade or so after the death of Isaac Newton (who was born the year Galileo died). Even in Herschel’s time, you got hints of pre-scientific ideas still floating around. So Herschel believed the Sun was a planet like our own, with people living on it. He reckoned that if the solar inhabitants looked at our own planet, they would perceive it as a fiery ball, like we do the Sun. The roots of this idea, of course, are in the classical Greek elements. Even though Earth had been displaced from the centre of the universe, fire still had a tendency to rise heavenward, and this was where the great Herschel got his unscientific idea.

There is lots more fascinating stuff in Clerke’s book which I recommend you read or listen to yourself. The author is an interesting person in her own right. She wrote several other books on astrophysics and cosmology, and is one of the foremost science popularisers of the 19th century in spite of of having no university degree or even any formal schooling. But then, orthodox routes to learning were very limited for women of the time. She was the daughter of a bank manager in Skibbereen and got interested in astronomy as a child, while the elder Herschel was still alive. She was home schooled by her parents, her father being a graduate of TCD, and an amateur astronomer. He owned a transit telescope which would have provided a time service to the townsfolk of Skibbereen in the days long before standardised time zones. The younger Clerke got to view the planets through this instrument and studied astronomy at home in addition to Latin, Greek, and maths. In her twenties she lived in Italy where she was also able to study science (though her first published article was on the Sicilian mafia!).

Later in London Clerke became a successful popular science writer. This gained her many connections with scientists of the time, and her circle grew to include astronomers from across Europe as well as South Africa, and major universities and observatories in the USA. She got to spend time at observatories and became something of an expert on spectroscopy.She was a member of the British Astronomical Association, but later became a member of the Royal Astronomical Society and the Royal Institution. She was only the third female member of the RAS, after astronomer Caroline Herschel (brother of William and aunt of John) and Mary Somerville, another self-motivated student and friend of the Herschels. And that reminds me, my next reading or listening project has to be the [*Memoir and Correspondence of Caroline Herschel * (https://librivox.org/memoir-correspondence-caroline-herschel-by-margaret-herschel/), written by John’s wife Margaret Herschel in 1879.


#1176

Next Friday, July 27th, we get a total lunar eclipse visible from Ireland. The maximum eclipse depth is reached just before moonrise on the east coast. (Moonrise is about 10 to 15 minutes later on the west coast). Loads more info about timings etc. [*here * (https://www.timeanddate.com/eclipse/lunar/2018-july-27) – for information specific to your location click the link near the top of the page that says “Is this Total Lunar Eclipse visible in ?”.

Just bear in mind that you want to be somewhere with a view down to the south eastern horizon, as the eclipse is total as the moon rises. In Dublin, that’s at 9.22pm, with the total eclipse continuing for another 50 minutes before the earth’s shadow starts to move off. Because it’s low to the horizon, you’ll also get the [*moon illusion * (https://en.wikipedia.org/wiki/Moon_illusion), which makes the moon look weirdly huge. To see the horizon you either want to be on an elevation (which doesn’t have to be very high up) or be on the south or east coast.

In south Dublin, one of my favourite spots for watching moon rises is Dun Laoghaire pier. You don’t have to walk very far, and you can do it with a Teddy’s icecream in your paw. For this particular moonrise, the direction is 123 degrees, measured clockwise from north. Standing at the bandstand on the east pier gives you an unobstructed view of the moon rising out of the sea just beyond the 40-foot in Dalkey. And as a bonus from this location you will also be able to see the pretty sunset in the northwest, five minutes after moonrise. Here’s hoping for clear skies!


#1177

Actually, this eclipse has a whole bunch of bonuses. Three planets prominently visible in the south (Mars rises below the Moon just as the total eclipse ends). There’s a really bright flyover of the International Space Station just at the end of the partial eclipse, and the ISS passes within 0.25 degree of Arcturus, the brightest star in the (northern) sky. And the eclipse itself is the longest duration lunar eclipse of the 21st century!


#1178

Thanks for the heads up PS!

After reading your post , I saw this (no idea if it is rue or not):
scienceinfo.news/july-27-201 … -the-moon/


#1179

Not. Pretty much every sentence is a hoax.


#1180

Apparently this hoax has made rounds for at least a decade - here’s a iflscience link: iflscience.com/space/no-mars … night-sky/

Mars is what about double the size of the moon (6,779 vs 3,474 km according to the internet) so: