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 much this past month. Aurora have been seen and photographed, Comet Leonard is approaching visual visibility – I think I picked it up in binoculars on a strongly moonlit night a week or so ago – but I may have been kidding myself! Orion is now prominent, so some fun to be had there if the clouds disappear. Jupiter has been looking nice but is now getting rather low for good clarity.
On a practical society note, we have the AGM this coming Thursday, December 2nd @7pm, along with David’s astro-quiz. The night will only be on Zoom and not in hybrid format, so don’t turn up at the museum, there will be no one there. Should be a fun night – no pressure David. Festive hats are not a dress-code requirement, but here is nothing to stop you!
Ian Bradley, on behalf of the EAS committee.
Recent images – Ian BradleyAbove: November 24th. The great Red Spot is just visible and the Moons Io [left] and Europa [right}. Click toenlarge.
Astronomy News – David Glass
At the moment there seems to be a pause in the construction around the launch area, with a lot of cranes etc taken off site. The massive tower holding the “chopsticks” intended to catch an incoming booster and position a starship on it are essentially complete, and much of the scaffolding around it has been taken away. On 12/11/21, all six Raptor engines on Starship 20 were test-fired. There is also a booster rocket (BN4) in the launch area which has Raptor engines fitted, but BN5 in the construction area is catching up fast and it’s not clear which one will be used for testing and a future launch. There’s a very nice discussion of what’s happening here.
At the moment it’s unlikely that there will be a launch to orbit in 2021, but we can look forward to more tests and possibly test flights of booster and starship separately.
Another outfit has joined the select group who have put a craft into orbit. This time it’s Astra, who used their relatively small rocket to put a test payload into 500 km high orbit. This was achieved after just 5 years’ development. Their aim was to develop a small 2-stage rocket and launch system that can be mass-produced and launched from spaceports anywhere on the planet. This “Rocket 3” development can carry a 50kg payload to orbit, and a planned “Rocket 4” should be able to carry up to 200kg.
The launch site for this was Kodiak Island in Alaska, which emphasises the wide range of launch sites that could be used for this rocket.
James Webb Space Telescope
The launch of JWST will be a huge event in astronomy and astrophysics, which so many science goals depending on its successful launch, deployment and commissioning. So, the last thing that people want to hear right now is that a failing clamp sent an unexpected vibration through the spacecraft – which is precisely what happened. Engineers seem to be quietly confident that everything is OK with the spacecraft, which is robust enough to withstand launch into space. However, nobody needs that additional stress! The planned launch date in December may slip a bit, but we will have to wait and see.
We all know that there are near-earth objects (NEOs) orbiting the Sun. At the moment none of these pose a significant risk to the Earth (although the name Apophis does pop up in news articles from time to time!), but one day we may detect one that could collide with the Earth. So, what can we do about it? The Double- Asteroid Redirection Test (DART) is designed to see whether the course of a smallish asteroid can be deflected by a spacecraft impacting it, and its spacecraft was launched this month to intercept a binary asteroid, 65803 Didymos. The larger of the bodies is about 780km across, but the smaller one is about 160km across. This a size of interest in terms of protecting the Earth, because there are a lot of them and not all of them have been detected yet. The aim is to create a small deflection by crashing the spacecraft into the smaller body. The deflection should be measurable by tracking the asteroid from Earth, and there’s already been an intense campaign of observation to determine its current track.
There’s a nice description of the mission here.
And, if you want to become a certified “Planetary Defender”, you can take quiz!
Practising for the Search for Life on Mars (or Elsewhere in the Solar System)
Modern astrobiology depends on being able to recognise signs of life here on Earth, in order to spot it elsewhere in the Solar System (or possibly beyond – roll on JWST!). This means that astrobiologists can be found deep inside caves, in submarines at the deep ocean floor near hydrothermal vents, risking their existence near boiling volcanic lakes etc trying to gather samples of life in the most extreme environments known. A study published in October didn’t go this far, but concentrated on a hostile, arid environment that could represent conditions on Mars. They concentrated on finding compounds that are associated with cell membranes, proteins, and immune response. Key to this was the development of their “LDChip”, a single device for detecting key molecules which may find its way onto future spacecraft.
The rocks they investigated were carbonates from the Atacama Desert, Chile (where the ALMA telescope is located). The rocks are thought to be from between the Triassic and Jurassic eras, when a huge mass- extinction event occurred. The results showed limited signs of life, associated with cell shutdown and survival in harsh conditions which could be expected if a mass-extinction event was underway.
The full paper on this research is here.
But a summary with more detail than in this newsletter can be found here.
New Ion Propulsion System Using Iodine, not Xenon
Several spacecraft have been powered by ion-propulsion systems, where an electric field is used to accelerate ions to create a thrust. The Hyabusa-2 spacecraft which successfully got samples back to Earth from the asteroid 162173 Ryugu used one. The thrust from these systems is tiny, about that of the downforce of a small hedgerow bird sitting on a branch. However, the thrust can be applied for months at a time and the effect on a spacecraft’s trajectory is dramatic.
Traditionally, these systems have used xenon gas (relatively heavy atoms) to provide the ions. However, a team has now developed an ion-propulsion system that uses iodine instead, which is abundant on Earth and produces more thrust than a xenon-based system so less propellant mass is needed for the same job. A downside though is that iodine is corrosive, so electronics and other potentially-affected systems on a spacecraft have to be protected adequately. The new system has been tested aboard a 20kg Cubesat launched from China in November 2020. A full description of the engine and its performance can be found in an article in Nature (getting published there is an achievement in itself!), available in full here.
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 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||Optimium magnification|
|η Cas||00h49m||+57° 49′||3.5||7.2||13″||317°||1.7||GO, K7||58x|
|1 Ari||01h50m||+22° 16′||5.9||7.2||2,9″||164°||3.5||K1, A6||268x|
|γ And||02h04m||+42° 20′||2.1||4.8||9.8″||64°||3.5||K3, B8||77x|
|ι Tri = 6 Tri||02h12m||+30° 18′||5.3||6.7||4″||69°||1||G5, F5||188x|
|η Per||02h51m||+55° 54′||3.8||8.5||22″||301°||3||K3, A3||27x|
|32 Eri||03h54m||–02° 57′||4.8||5.9||7″||254°||2.6||G8, A2||107x|
|ρ Ori||05h13m||+02° 52′||4.6||8.5||7″||64°||1.7||K3, F7||107x|
|14 Aur||05h15m||+32° 41′||5.0||7.4||15″||226°||0.4||A9, F3||50x|
|ι Ori||05h35m||+05° 57′||2.9||7.0||10.9″||142°||0.2||O9, B1||69x|
|ι Cnc||08h47m||+28° 46′||4.0||6.6||30.6″||307°||2.6||G8, A2||25x|
|ζ Lyr||18h45m||+37° 36′||4.3||5.6||44″||150°||1.1||B7, A8||17x|
|Albireo||19h31m||+27° 57′||3.4||4.7||35″||54°||3.5||K3, B8||21x|
|31 Cyg||20h14m||+46° 44′||3.8||4.8||107″||325°||29||K2, B3||7x|
|β Cap||20h21m||–14° 47′||3.2||6.1||307″||267°||3.2||K0, B8||4x|
|γ Del||20h47m||+16° 07′||4.4||5.0||9″||67°||1.4||K1, F7||83x|
|δ Cep||22h29m||+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.