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#179 - Telescope Special


As I told a friend of mine once who asked me why I joined Mercury, I think if I had been alive 150 years ago, I might have wanted to go out and help open up the West.

Born April 3rd 1926 – Gus Grissom Apollo 1 astronaut (d. 1967)




Venus is going to appear inside the seven sisters (Pleiades) cluster on the 3rd!!! ..in Japan, it is known as Subaru (the logo for the cars is the seven sisters!!, curiously I only count 6 stars on it) In Japan, the constellation is mentioned under the name Mutsuraboshi ("six stars") in the 8th-century


The International Space Station and Starlink satellites over Exminster on Sunday night (Image: Adrian Wood)

ISS and Starlinks being making a lot of people very excited in the UK as we’re getting quite a bit of flyover action!!!



And Modern meteorology was born 60 years ago this week with the launch of Tiros and the first TV pictures from space.












SpaceX releases a Payload User’s Guide for its Starship rocket

  • Fully Reusable the rocket can deliver more than 100 metric tons to low-Earth orbit and 21 tons to geostationary transfer orbit.

  • refuel Starship in low-Earth orbit with other Starships, enabling transportation deeper into the Solar System for 100 tons or more

  • payload fairing in the cargo configuration of the vehicle, with a width of 8 meters and an extended volume capable of encompassing payloads as long as 22 meters

  • For human flights of up to 100 people, according to the document, "The crew configuration of Starship includes private cabins, large common areas, centralized storage, solar storm shelters, and a viewing gallery."

Poll with the Patrons ...they were going with a 2022 maiden voyage, I chickened out and went with a 2025 number ..I’d be more comfortable putting money on mine!!



OneWeb filed for bankruptcy ...we’ll see what that means.

Not surprising as the world faces disruptions to capital, supply chains, and god know what else. So a delay in the deployment of the satellites is inevitable and that will mean loss of revenue too. Eric Berger reporting on this pointed out that Gwynne “the steady hand at the Tiller” Shotwell at SpaceX pointed out Trying to build a network without a low-cost launch, she suggested, could be financially disastrous. “If you’re thinking about investing in OneWeb, I would recommend strongly against it," Shotwell said in October. "They fooled some people who are going to be pretty disappointed in the near term."




Light Telescopes Special

  • To be thought of as a science god you must be associated with a telescope. Galileo, Newton and Einstein are. ...here is s little history.

  • 1608 patent submitted to the government in the Netherlands by Middelburg spectacle maker Hans Lippershey for a refracting telescope (unlikely to be inventor, but said he saw some kids using two lenses to makes things closer) x 3 magnification

  • 1609 news had spread to Galileo who set about making his own and got to x10 magnification - and BOOM modern astronomy was born and he became the first person to see the moons of Jupiter!!! Galileo Galilei was the first astronomer to view the Pleiades through a telescope too

  • Glass has loads of problems, if it gets too big it sags, and also the colours don’t bend at the same rate, hence rainbow colours through thick glass prisms ...see Pink Floyd Dark Side of the Moon cover. (spherical aberration and chromatic aberration)

  • People started thinking about using mirrors to get around this.

  • In 1668, Isaac Newton built the first practical reflecting telescope, the Newtonian. So Jamie when I tell you I have a nice 8inch Newt, don’t freak out again.

  • The invention of the achromatic lens in 1733 sort of corrected color aberrations, silver coated glass mirrors in 1857 and aluminized mirrors in 1932

  • all meant that these telescopes were slowly being improved and getting better, but then we reached a limit which is roughly

  • maximum physical size limit for refracting telescopes is about 1 meter (40 inches)

  • The largest single mirror refractor is 8.2m or 323 inches, like the Subaru in manukea and the VLT telescopes in Chile

  • But you can make bigger refractors by making them with multiple cell mirrors, like james webb etc, each of these cells has to be controlled by computer in shape and position to keep the cluster in focus!!!!

  • So from the 20th century has been dominated by reflectors, which are getting bigger thanks to design using segmented mirrors

  • Largest at the moment is Gran Telescopio Canarias (GTC) in the canary islands at a whopping 10.2 metres or 409 inches

  • Future Telescopes

  • Large Synoptic Survey Telescope 8.4 m (first light planned in 2020 and full operations beginning in 2022)

  • Giant Magellan Telescope 7 × 8.4 m mirrors giving a 24.5 m aperture with 21.4 m light gathering area (first light planned in 2021 and completion in 2025

  • James Webb Space Telescope 6.5 m (March 2021 launch planned)

  • European Extremely Large Telescope 39.3 m (first light planned in 2024)

  • Thirty Meter Telescope 30 m (first light planned in 2027)

  • OLT Overwhelmingly large telescope was cancelled.




Spiralling cost!!!

Yes, you get better resolution with bigger telescopes but the cost grows quadratically with size, so there is a major downside here. The Crisis in Astrophysics no less

25 m GMT price = 1 billion dollars

30 m TMT = 2 billion dollars

100 m telescope would cost about $35B,

A similar situation is true for space-based observatories, where the ∼$10B 6.5 m JWST provides an example of how the funding prospects of yet larger telescopes look unlikely


In the 2030s we might see the launch of the James web successor the LUVOIR.The Large UV/Optical/IR Surveyor (LUVOIR) is a concept for a highly capable, multi-wavelength space observatory with ambitious science goals, from the epoch of reionization, through galaxy formation and evolution, star and planet formation, to solar system remote sensing. LUVOIR also has the major goal of characterizing a wide range of exoplanets, including those that might be habitable - or even inhabited.

So what’s next and what about Einstein!!

Gravitational Lens of the Sun: Its Potential for Observations and Communications over Interstellar Distances - VON R. ESHLEMAN seminal paper discusses another way to bend light, as Einstein predicted, 1919 expedition led by Eddington confirmed general relativity's prediction for the deflection of starlight by the Sun during the total solar eclipse of May 29, 1919. The era of Gravitational lensing had begun!!!

  • As the Sun bends the fabric of space and object follow a curved path around it (orbits in the case of the planets) so light is also bent.

  • The gravitational field of the sun acts as a spherical lens to magnify the intensity of radiation from a distant source along a semi-infinite focal line.

  • A spacecraft anywhere on that line in principle could observe, eavesdrop, and communicate over interstellar distances, using equipment comparable in size and power with what is now used for interplanetary distances.

  • If one neglects coronal effects, the maximum magnification factor for coherent radiation is inversely proportional to the wavelength, being 100 million at 1 millimetre.

  • at the 203 GHz wavelength, amplification of 1300,000,000,000,000.(one point three quadrillions) 1300 Trillion x Magnification

  • The principal difficulties are that the nearest point on the focal half-line is about 550 AU separate spacecraft would be needed to work with each stellar system of interest

  • At 550AU the orbit takes about 15000 years. ...gross.

  • The solar corona would severely limit the intensity of coherent radiation while also restricting operations to relatively short wavelengths of light

Italian astronomer Claudio Maccone suggested that this should be enough to obtain detailed images of the surfaces of extrasolar planets. …SAY WHAT?


So you want to look at Kebler 438b, the most Earth-like exoplanet, at a resolution of say 1000 pixels across its surface? 7135 Km diameter at a distance of 640 light-years using angular size =206,265x(diameter/Distance) means an angular diameter of 2.43e-10 arc seconds or about 1.2 x 10-15 radians, (oh dear Blackhole was “only” 1.2 x 10-10) meaning that means since the resolution of your telescope is about λ/D, at optical wavelengths around 500 nm, you find you would need to build a telescope with diameter D = 208,000 km! Bigger than Jupiter!!! About a quarter of the suns size!!



Fast Outgoing Cyclopean Astronomical Lens (FOCAL) is a proposed space telescope that would use the Sun as a gravity lens at 550 AU (the Voyager 1 and Voyager 2 probes are only at distances of 148 AU and 123 AU at the moment


A gravity lens will bend objects behind it, so that images from the telescope would be difficult to interpret.

  • FOCAL would be able to observe only objects that are right behind the Sun from its point of view, which means that for every observed object a new telescope would have to be made

  • interference of the solar corona, which will make the telescope signal-to-noise ratio poor,

  • the high magnification of the target, which will make the design of the mission focal plane difficult, and an analysis of the

  • inherent spherical aberration of the lens will limit the resolution possible.


Bonus Uses though

  • measure stellar distances by parallax, which would be using the baseline of 550 AU, measure the precise position of every star in the Milky Way,

  • study the interstellar medium

  • the heliosphere,

  • observe gravitational waves,

  • check for the possible variation of the gravitational constant,

  • observe the cosmic infrared background,

  • characterise interplanetary dust within the Solar system,

  • more precisely measure the mass of the Solar system


But a paper that came out on Wednesday and at first I thought it was an April fool;

Resolving Exo-Continents with Einstein Ring Deconvolution

Instead of using the entire telescope as a single pixel detector, measuring the Einstein Ring’s total brightness at various locations, we propose an instrument concept which could measure the azimuthal variations in the intensity of the Einstein Ring. This additional information could improve the reconstruction performance for a sparsely sampled and time-variable image.


  • A mission to the focus of the solar gravitational lens could produce images with unprecedented angular resolution and sensitivity.

  • The Earth viewed from the view of a geostationary weather satellite. Over the course of a day, the thermal response of the North American continent for example is evident, as the land mass rapidly heats and cools in response to the changing solar insolation and is visible on a daily timescale.

  • In the context of trying to resolve the time variable thermal signature of continents on other Earth-like exoplanets, they develop an approach to improve the image reconstruction performance by using azimuthal variations in the Einstein Ring's intensity.

  • In the first post-Newtonian approximation to General Relativity, an arbitrary disk intensity distribution in the source plane is mapped to a narrow annulus around the Einstein Ring, with each azimuthal element corresponding to a sector in the disk.

  • A matrix-based linear measurement model at various fixed signal-to-noise ratios demonstrates that this extra information is useful in improving the reconstruction when the image is sparsely sampled, which could improve integration times and temporal errors.

  • The planet is spinning as you are taking measurements.

  • To extract the signal from the Einstein Ring, extremely efficient suppression of solar noise contribution is required, such as an advanced coronagraph or starshade which has been optimized for blocking sources with extended emission perhaps in addition to a secondary off-axis imager for reference subtraction of the noise from the solar coronal emission,

Conclusion

  • A detailed instrument design and mission plan to resolve exocontinents would need to evaluate the requirements in detail to ensure that a reasonable level of SNR for each azimuthal resolution element could be acquired rapidly enough.

  • Viewing a planetary system is by no means still life photography. Surface albedo changes on timescales of minutes and hours by rapidly evolving weather patterns, as well as on timescales of days and months as the planet rotates around its own axis

  • as well as around its hoststar, modifying its apparent “lunar phase" in wavelengths where illumination from the host star are dominant

  • Trade-offs between sensitivity and wavelength resolution in a spectrographic mode could be considered in the context of science questions,

  • such as resolving photosynthetic vegetative regions with a red edge,

  • extraterrestrial cities and their corresponding greenhouse gas emission

  • artificial illumination during night

  • it may be worth considering if a trajectory to acquire multiple planets colocated in a multi-planet system such as Trappist-1



But Hold your horses our previous guest and astronomy wonder David Kipping has another idea!!!

Don’t use gravity to bend light but use the atmosphere!!!

Refraction through the Earth’s atmosphere to approximately one lunar separation has been known since the 18th century (Cassini 1740), through studies of the lunar eclipse. The use of this for lensing is first hinted at by von Eshleman (1979) again


THE TERRASCOPE

The "Terrascope": On the Possibility of Using the Earth as an Atmospheric Lens

David Kipping studied the green flash as a masters student at Cambridge

As we know from his Halo drive Kipping is really interested in using natural phenomena and co-opting these as technology, using a black hole as a means of propulsion for example, and he also then wonders how advanced civilisations may use this.

When he was doing the maths as to what causes the green flash phenomenon, he did an illustration that at some point where you have a solar eclipse with the Earth as the eclipser, then around the earth will be a green ring, he even photoshopped a version for the cover of his thesis.

But what he did realise at this point is that the sun is bending the light through the thick atmosphere and there will be a place where this will focus,

For the earth grazing line, it will be about ⅔ of the way to the moon, but these are likely to be absorbed by the atmosphere, reflected by clouds etc.

If you look at the infrared then it just so happens that a position on the moon might actually be viable


What Kipping actually advises here is a telescope at the hill sphere radius (where your Lagrange points are)

The light is only going through the very upper atmosphere, reducing clouds, and turbulence and absorption etc.

This paper aims to provide the first quantitative grounding for the Terrascope concept by calculating the amplification expected,

  • a 1 metre Hill radius “Terrascope” is calculated to produce an amplification of about 45, 000 x for a lensing timescale of ∼20 hours.

  • In practice, the amplification is likely halved in order to avoid daylight scattering i.e. 22, 500 (∆mag=10.9) for W =1 m, or equivalent to a 150 m optical/infrared telescope.


As an initial quantification of these effects, the goal here is not to perform the most realistic calculation possible, but rather estimate the approximate effects that might be expected. Other effects not modelled, such as airglow, pointing stability and turbulence are briefly explored in the discussion.







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