A pdf version of this member’s newsletter which includes an additional section on EAS business and developments is issued to all current members.
See also our monthly Sky Notes for objects observable in the sky from Kendal during this month.
Welcome to the December newsletter. Sadly, on many fronts, the Covid crisis continues, so I hope you all managing to keep well and keep occupied. The weather clearly hasn’t cooperated at all this month. I’ve managed to successfully capture the Orion Nebula, M42, rather close to full Moon using narrow band Hα filter as a test sequence and some views of Mars early in the month. I tried several times later on, got on target only to have to rapidly dismantle as it started raining! It’s so frustrating, I sometimes wonder why I bother! I hope some of you have had better luck.
You will have received from Clive, formal notification of our Annual General Meeting in early January. Obviously, this will have to be by Zoom. The technology is sophisticated enough for you to be able to contribute so I have no doubt that this will be successful. The [short!] AGM will be followed by Prof. Lionel Wilson speaking on “Volcanism on Venus – not quite our twin planet”. What I wish to add here, is that we are losing two officers this year; both Clive and Phil are stepping down after several years of service. I want you to remember that this is your society and that it can’t function without input and, yes, some effort from the membership. Please consider if you could step up and contribute to one of these, or any other, roles
On a positive note, in August, we were approached to contribute to a consultation by a group of MP’s, the All Party Parliamentary Group for Dark Skies, asking for input. I responded on behalf of the Society and heard today that they will publish a policy document on December 9th. Of course, such things have little impact on Government policy, but at least it flags up in Parliament that there are concerned MP’s and voters, so we will see if there is any long-term effect. If you are interested in what you can do to reduce light pollution, have a look at The Institution of Lighting Professionals website, in particular.
Ian Bradley, on behalf of the EAS committee.
We’ve circulated this by email before :
- Gresham College free Astronomy lecture series by Professors Katherine Blundell and Roberto Trotta. See the Gresham College site and have a look for these and other events. Not all of these are on astronomy.
Astronomy News – David Glass
SpaceX are building Starships as a cheap and re-useable way of getting people and equipment into Earth orbit and beyond. Starship SN8 (design surely not inspired by Fireball XL5?) was looking to be close to a “hop” to an altitude of 15km and a soft landing at the beginning of November. They did a static test fire of the three giant Raptor engines beforehand on 12/11/20 – and something melted. The images below show the very brief test fire in progress, and the situation just after shutdown with something molten dripping to the ground…
You can see the whole thing captured this video.
Starship SN8 is currently in position for launch, and a new Raptor engine is in place.
A successful test firing took place on Tuesday 24/11/20
A scheduled date is visible in the image above of 30/11/20 sometime between 13:00 and 00:00 UK time for the “hop”, so watch out for it!
World news in November also featured the successful launch of SpaceX’s Crew 1 capsule on a Falcon-9 rocket (also powered by Raptor engines), which went very well. The capsule docked successfully with the ISS, and the first stage booster landed successfully on the drone ship in the Atlantic. This marks the transition to
full commercial operation for the capsule, which can ferry people and equipment to the International Space Station. On the way to the ISS, a “zero-gee indicator” was deployed within the capsule by the crew…
Apparently, the use of zero-gee indicators goes right back to the first crewed spaceflight, when Yuri Gagarin released a small doll in the Vostok 1 capsule to prove microgravity conditions while in flight. Bearing in mind that humans have been propelled into space for nearly 60 years now (Vostok 1 was launched in 1961), it does seem right to call it a tradition! The whole Crew 1 launch is available on a 4 hour long Youtube to watch if you missed it – it really is amazing.
A mission to retrieve around 2kg of Moon rock was launched from China on 23/11/20. The Chang’e 5 mission intends to deploy a robotic lander which will drill down to a depth of about 2m to retrieve pristine material, and scoop material from the surface. The lander also has instruments for analysing the surface. The landing zone is on the near side of the moon, where the surface is predicted to be around 1.2 billion years old (compared to the Apollo samples which go back to around 3 – 4 bllion years). The lander will be deployed from an orbiter, and an ascent vehicle with the lander will carry the rock back to the orbiter which will then head back to Earth. The rocks will be transferred to a sample return capsule for return to Earth’s surface in mid-December. All this is being done robotically, which will be an impressive feat.
For a neat animation of how the sampling and return to Earth is intended to happen, see here.
Tragedy at Arecibo
The Arecibo radio telescope in Puerto Rico has been at the forefront of radio astronomy and atmospheric studies since 1963, and as well as contributing to the SETI programme it has featured in notable film and TV appearances such as Goldeneye (1995) and a very creepy episode intro for the X files: see here.
The 305m dish, needed to achieve the required angular resolution and sensitivity at the radio frequencies of interest, has suffered damage in the past but had been repaired. However, the breakage of two cables holding up the receivers within a short space of time left the dish beyond economic repair. Two such failures in close succession could mean that all the cables are weaker than they should be. The decision has now
been made to decommission the telescope.
Fortunately, radio astronomers are not left without observing tools of this power. The FAST telescope in China, based on similar design principles to Arecibo, became fully operational this year and has a 500m dish. There is also the multiple-dish Very Large Array (VLA) in New Mexico, USA, which uses interferometry to achieve high angular resolution. Other smaller telescopes are also available including the Lovell Observatory in Cheshire, which can work together to form a giant interferometric telescope.
Phosphine in the Atmosphere of Venus
On 14/9/20, a team of astronomers led by Prof. Jane Greaves of Cardiff University announced the detection of phosphine (PH3), an organic molecule associated with biological processes, in the atmosphere of Venus ( see here for a version of the paper). They used observations from the ALMA interferometric telescope in Chile and the James Clerk Maxwell Telescope (JCMT) in Hawaii for this. A dip in brightness in the spectrum of Venus at a wavelength near 1mm was seen with both telescopes
This is exciting, as it could indicate microbial activity in Venus’ atmosphere. Another study, looking at data from the Pioneer satellite, also indicates that phosphine could be present: see here.
However, nobody expected the response from groups within the astronomy community. During October, three papers were released on ArXiv claiming that the detection is false:
One paper stated that the spectral line detected is from sulphur dioxide (SO2), while the others could not extract the phosphine spectral line in the data. Another paper put an upper limit on the concentration of phosphine that is below what was measured, see here.
The original team did not take this lying down. In a subsequent paper, the team re-analysed the data taking into account the methods and findings in the October papers – and still found evidence of phosphine (although it was at lower concentrations than previously thought): see here.
The papers also stress that better observations are needed to really confirm the result. It would also be great to send a spacecraft to actually sample the atmosphere.
All of the above shows a useful process at work, where findings in papers are challenged (hopefully in a constructive way!) and results are updated to reflect new knowledge and approaches. Studies like these are out to get at the truth, and sometimes that can be frustrating!
The Blue Ringed Nebula – Ian Bradley
I typed the title and it immediately brought to mind a humorous Australian song – I’ll say no more other than suggest you Google ‘blue-ringed octopus song’. To paraphrase another comedy act, and now for something completely different and serious.
Just over a week ago, an article in the journal Nature caught my eye; a discussion on observations of the Blue Ringed Nebula – with the exciting star having the formal name of TYC 2597-735-1. This rather delicate and pretty object, which is what caught my eye, resembles a planetary nebula but is actually the result of a recent (a few thousand years ago) stellar merger.
The [complicated] 15’ x 15’ false-colour image is a mixture of far-UV, near UV and Hα images from the GALEX spacecraft. The image shows two clear rings radiating at the Hα wavelength (red) – in other words excited hydrogen atoms plus a far-UV emission (blue) and a shock front visible in near-UV. The small insets labelled b, c & d show the object in the three wavelengths bands studied. The Hα emission, radial-velocity variations, enhanced ultraviolet radiation and excess infrared emission suggest the existence of a dusty circumstellar disk. The blue ring comes from fluorescing hydrogen H2 and only appears where the ejected two cones overlap in our line of sight as can be seen at bottom right. The speed of the outflow is 400km s 1 – 0.1% of the speed of light!
What their modelling suggested is that matter flowed from the larger star onto the companion resulting in the companion star spiralling inwards, and eventually merging. Most of the ejected matter ended up gravitationally bound and formed a circumstellar disk which eventually cooled and formed dust. The merger ejects more material but this is shaped by the circumstellar disk leading to the two cone structures. This ejected material sweeps up interstellar material and the resulting shock front causes the Hα emission.
This object provides a unique opportunity to study post-merger behaviour. See the original paper and for a clearer picture of what is going on.
Neutrinos from the CNO fusion cycle in the Sun detected – Ian Bradley
Our Sun is a natural fusion reactor, and fusion releases neutrinos. There are millions per second of solar neutrinos passing through your fingernail but they don’t interact. In the late 60’s Ray Davis used a tank of perchloroethylene, dry cleaning fluid, deep underground to detect neutrinos – and there were too few compared to what was expected – the solar neutrino problem. That mystery was solved in the 90’s. So now what is new?
In a star like our Sun, it was expected that the dominant fusion process is what is called the p-p chain, where a pair of protons fuse to create deuterium, which then fuses with a third proton to create helium-3. Finally, two helium-3 nuclei fuse to create a helium-4. This process, and two other slight variations, produce 99% of fusion energy in the Sun. However, it was believed that a rare alternate process, called the CNO cycle, should produce the remaining 1%, but there was no evidence for this process. It is important to understand this process too because in higher mass stars, stars over 1.3 times the mass of the Sun, it was expected to be the dominant process.
The CNO cycle is a fusion of protons with carbon, nitrogen and oxygen nuclei in a six-step process that creates one helium-4 nucleus before repeating itself. It produces a different and distinct neutrino spectrum compared to that from the pp chain. And that it what the Borexino collaboration has now measured.
This experiment has a 280 tonne scintillator target, and detects solar neutrinos when they collide with electrons in the scintillator. As the electron recoils it produces light, which is captured by an array of photomultiplier tubes. Despite the enormous neutrino flux, only tens of neutrino are detected daily. The experiment is deep below the Gran Sasso mountain in Italy to shield it from the vastly larger cosmic ray signal. After a difficult and technical analysis, the Borexino team have now confirmed the tiny signal and is consistent with the expected 1% of the Sun’s energy production by this route. It also opens a door to answer the questions about the ‘metallicity’ (elements other than hydrogen and helium) of the Sun – but needs more data and probably a new improved detector.
Constellation of the month – Moira Greenhalgh
This month I have chosen Perseus. It is circumpolar and can be seen most of the year, but it is particularly good now. So, what does it look like, and how do you find it?
The W of Cassiopeia is clearly visible in the NE just after dark, moving to E by about 8.00 pm. The constellation of Perseus is just below.
Perseus was the Greek hero who slew the gorgon Medusa. She had snakes for hair and anyone looking at her turned to stone. [Digression – jellyfish are called Medusa after her]. Perseus got around this by not looking directly but using his shield as a mirror. He is always shown in pictures carrying her head and usually holding a mirror. The star Algol is her evil eye. He then rescued Andromeda from the sea monster, Cetus, a story
with a long history, as shown on the vase.
Most of the Perseus family of constellations are part of this myth, Cassiopeia and Cepheus were Andromeda’s parents, and Pegasus, the winged horse, was supposed to have sprung from the body of Medusa.
Back to the constellation. It was one of the 48 ancient constellations listed by Ptolemy in the 2nd century, and is 24th in size of the 88 modern constellations.
The brightest star is Mirfak (α Persei), a yellow-white supergiant, magnitude 1.79, located around 590 light years from Earth. It and many surrounding stars are members of an open cluster, the Alpha Persei Cluster.
The most well-known star is Algol (β Persei), Medusa’s evil eye. Algol means “the Demons’ head” in Arabic. In Hebrew tradition it is known as “Satan’s Head”. Very ominous. Around 92.9 light-years from Earth, its magnitude appears to vary from 3.5 to 2.3 over a period of days, and this is visible to the naked eye. It was thought to be an eclipsing binary system but a third star makes it a triple star system. The two main stars are very close together, 0.05 AU, and the main dip in brightness is when the larger, fainter passes in front of the hotter, brighter primary star. It gives its name to a group of eclipsing binary stars known as Algol variables. Around 7.3 million years ago Algol passed within 9.8 light years of the solar system, when its apparent magnitude would have been around -2.5, very much brighter than Sirius is today.
At least 7 stars in Perseus are known to have exoplanets
The Perseus Arm is a spiral arm of the Milky Way, towards the rim of the galaxy, which stretches across the sky from Cassiopeia through Perseus and Auriga to Gemini and Monoceros. Within this arm are two open clusters known as the Double Cluster, NGCs 869 and 884. They lie in the sky between Cassiopeia and Perseus and are easy to find.
Clearly visible in binoculars, they make a wonderful sight through an amateur scope, with both clusters in view.
Other Deep sky objects include open cluster M34, which is best viewed through a telescope. The Little Dumbbell Nebula, M76, is a planetary nebula and emission nebula NGC 1499, which is known as the California Nebula. There are also a host of galaxies.
The Perseids are an annual meteor shower in mid-August which were always a highlight of my childhood holidays in W Wales. They are associated with comet Swift-Tuttle.
Cepheid variables and distance – Ian Bradley
At our November Zoom meeting, there was a brief discussion following Richard Rae’s talk about how Cepheid variable stars were used to determine the distance to the Andromeda Galaxy, M31. Given some confusion, I thought it might be worthwhile to write something on the topic…
Cepheid’s are one of over a dozen different types of variable star types and are particularly useful as a so-called ‘standard candle’. They are a particular class of [short period] regularly pulsating stars where the varying light output is determined by something internal to the star.
Henrietta Swann Leavitt was looking at Cepheid variable stars in the Small Magellanic Cloud, a tiny close galaxy that orbits our galaxy, and noticed that there was a relationship between each star’s pulsation period and its brightness (apparent magnitude). She then assumed that all these stars were roughly the same distance away, with meant that this same simple relationship between the pulsation period and the luminosity (or absolute magnitude) of the star must also be true.
This is a stunning result as it implied from a measurement of the period you knew the absolute magnitude, so that a measurement of the apparent magnitude allows you to calculate the distance using the Inverse Square Law.
The problem was, no one knew the distance to the Small Magellanic Cloud so Leavitt couldn’t convert her apparent magnitudes to absolute magnitudes.
Apparent and Absolute Magnitudes
In ancient times, someone classified stars by their brightness to the eye. The brightest visible stars were given magnitude 1 and the faintest magnitude 6. Our eyes are logarithmic in sensitivity, so this ancient scale also is logarithmic, with each magnitude corresponding to about 2.5 times less light. This means there is 100 times less light from a mag 6 star as from a mag 1 star.
This brightness as seen from Earth is the apparent magnitude. To allow intercomparison between different stars at different distances, it is useful to compare their properties as though they were all at the same distance (10 parsec, ~3.3 light years). If the distance to the star is known, it is easy using the Inverse Square Law, to calculate how bright the star would be if it was at 10pc. This is known as the absolute magnitude.
The Inverse Square Law
The inverse square law is simply a geometric effect and describes the dimming as distance increases away from the light source. If the distance increases by some factor, the brightness dims by 1/factor2, hence the name inverse square law. For example, on doubling the distance of a star, the brightness drops by a factor of 4 but its magnitude increases by 1.5. Double distance again, and the magnitude increases by another 1.5
The solution was to find a Cepheid variable that is relatively nearby where measurement of the distance using parallax was possible. Once that was done, the apparent magnitude of that star and its distance allowed the calculation of its absolute magnitude. As this period and absolute magnitude of one Cepheid was now known, every other Cepheid period could be converted to an absolute magnitude and using the observed apparent magnitude, the distance could be calculated.
The Parallax Method
As the Earth goes round its orbit, nearby stars apparently move against the background of very distant stars. Measuring these tiny angular changes (for the nearest star Proxima Centauri, this is less than 1 second of arc) and using simple geometry, the distant can be calculated. This relies on knowing the distance from the Earth to the Sun (and that’s another story – the 1st step in the Cosmic Distance Ladder).
The great thing is that if you can now find Cepheids and measure their periods in other galaxies, we can deduce the distance of these stars and therefore that of their galaxies. It was this process that allowed the first reliable estimate of the distance to M31.
Winter Coloured Double Stars – Ian Bradley
Double stars can be very pretty, especially if the two stars have contrasting colours. Double stars have the advantage that they are little affected by light pollution or the phase of the Moon, unlike for example the faint fuzzy blobs of galaxies.
Splitting very close doubles can be an interesting challenge but you may be limited by the resolution of your optics. A very rough rule of thumb is that on an ideal night [do we get those in Cumbria?] your binoculars/telescope can resolve objects that have an angular separation of 140/aperture in mm [5.5/aperture in inches], so for a pair of 10×50 binoculars, you could separate stars if they are 140/50 ~ 3 arc seconds. I suspect 5 arc seconds might be a more likely possibility in this case.
Generally double stars with a colour difference are more interesting and beautiful to observe, especially if they are not too different in brightness. Having said that Castor, α Geminorum, is a pretty double with both stars being white and having a similar brightness.
One classic and the rather lovely double star is Albireo in β Cygni – the head of the swan.
The picture above is one I took in September using my 8” Meade SCT and a Canon DSLR. The primary star is a lovely golden yellow at magnitude 3.4 whilst the companion at magnitude 4.7 is a lovely blue colour. They are just splitable using a x20 magnification.
The annotated right-hand picture defines a few of the numbers in the table below. North is up as seen in binoculars, but be careful here as different styles of telescope with give different orientations (never mind the effect of a star diagonal!). For example, a Newtonian, Dobsonian or refractor will give west to the left and north down, whilst a Schmitt-Cassegrain or a Maksutov will give North up and East to the right [as will a refractor and a diagonal).
So what do the labels mean? The separation is just the angular separation in arc seconds of the two stars, whilst the position angle is the angle of the line joining the two stars measured going in a direction through east – so can vary from 0° to 350°.
In the table below;
- are the positional coordinates RA (Right Ascension) and DEC (declination), the equivalent of latitude and longitude;
- the magnitudes of the two stars;
- the colour difference where the bigger the number, the more distinct the difference, determined from the spectral class [colour] of the stars;
- Finally, the optimum magnification based on the opinion of Alan Adler. He found that doubles look their best at a magnification that is approximately 750 divided by the separation in arcseconds. So, for Alberio, where the separation is 35”, 750/35= 21, so 21x magnification looks best. This is a rather subjective measure and don’t worry if you can’t get this ‘optimum’. For example, with my Meade, my minimum magnification is 77x and Alberio looks great!
Sometimes, the human brain plays tricks on you. Despite the temperature of a star, which fixes the colour and the spectral class, if the brighter star has a strong colour, you perceive the fainter star to have the complementary colour [for red that is cyan] rather than its true colour! You’ve probably seen this with an afterimage after looking at a bright coloured object. This is a nice website on this point. And different people see slightly different colours just to confuse things even more.
The following is a list of winter coloured double star systems worth looking at for their colours, based on a 2016 article in Sky and Telescope by Bob King1 – who based his article on an earlier one by Alan Adler2. You might need some planetarium software to find some of these pairs.
|Star||R.A. Dec.||Mags.||Sep.||P.A.||Colour difference||Spec. Class||Optimum magnification|
|η Cas||00h 49m||+57° 49′||3.5||7.2||13″||317°||1.7||G0, K7||58x|
|1 Ari||01h 50m||+22° 16′||5.9||7.2||2.9″||164°||3.5||K1, A6||268x|
|γ And||02h 04m||+42° 20′||2.1||4.8||9.8″||64°||3.5||K3, B8||77x|
|ι Tri = 6 Tri||02h 12m||+30° 18′||5.3||6.7||4″||69°||1||G5, F5||188x|
|η Per||02h 51m||+55° 54′||3.8||8.5||28″||301°||3||K3, A3||27x|
|32 Eri||03h 54m||–02° 57′||4.8||5.9||7″||254°||2.6||G8, A2||107x|
|ρ Ori||05h 13m||+02° 52′||4.6||8.5||7″||64°||1.7||K3, F7||107x|
|14 Aur||05h 15m||+32° 41′||5.0||7.4||15″||226°||0.4||A9, F3||50x|
|ι Ori||05h 35m||+05° 57′||2.9||7.0||10.9″||142°||0.2||O9, B1||69x|
|ι Cnc||08h 47m||+28° 46′||4.0||6.6||30.6″||307°||2.6||G8, A2||25x|
|ζ Lyr||18h 45m||+37° 36′||4.3||5.6||44″||150°||1.1||B7, A8||17x|
|Albireo||19h 31m||+27° 57′||3.4||4.7||35″||54°||3.5||K3, B8||21x|
|31 Cyg||20h 14m||+46° 44′||3.8||4.8||107″||325°||2.9||K2, B3||7x|
|β Cap||20h 21m||–14° 47′||3.2||6.1||207″||267°||3.2||K0, B8||4x|
|γ Del||20h 47m||+16° 07′||4.4||5.0||9″||267°||1.4||K1, F7||83x|
|δ Cep||22h 29m||+58° 25′||4.1||6.3||40.9″||191°||2.5||G2, B7||18x|
Some recommended highlights:
- Eta (η) Cas: Exquisite at 64× with a pale-yellow primary and purple-red secondary.
- Alberio β Cas: Lovely yellow primary and blue secondary but some people see yellow and white!
- 1 Ari: A close pair. Orange and blue – a good example of complementary colour.
- 14 Aur: Yellow and pale orange; subtle.
- η Per: Reddish-orange and blue-green. Another example of complementary colour.
- 32 Eri: Yellow-orange and blue. A close pair, so use 100× or higher to see the colours more clearly. Could be a challenge to find.
- Iota (ι) Ori: Two pure white suns. No colour difference, so no false contrast here!
- Gamma (γ) Lep: Striking gold and green! Of course, since there are no green stars, the complementary perception effect is at play here. Sadly, this is quite low, below Orion, but worth a try
I’ve only seen a few of these but I hope to see some more. I hope you can see some too.