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¶What is Interferometry? April 10th was the one year anniversary of the first image of a black hole, taken with the Event Horizon Telescope using Very Long Baseline Interferometry (VLBI). Last week, the Event Horizon Telescope followed up with a detailed interferometry-produced image of the relativistic jets of gas produced by the supermassive black hole in Quasar 3C 279 (a blazar). What is interferometry? The resolving power (angular size of a feature that can be seen) of a telescope is determined by the size of its aperture due to the diffraction limit. After light (or any wave) passes through an aperture, it spreads out, fundamentally blurring the image—the blurring increases as the wavelength of the captured light approaches the size of the opening. In order to take radio images, where wavelengths are often measured in meters, you need enormous apertures, or you can combine many dishes to simulate a much larger aperture using a technique called interferometry. The challenge is in adjusting for and synchronizing the arrival times of signals over the dishes, taking into account their precise placement and the Earth’s rotation. In VLBI, the precise arrival time of signals is recorded using an atomic clock, and then the signals are later combined using a supercomputer that approximates the geometry of the system and searches for interference patterns in the data. The effective angular resolution of the Event Horizon Telescope using VLBI with dishes spread all over the planet (and in space!) is an incredible 20 micro-arcseconds (20 thousandths of a 60th of a 60th of a degree) — “enough to read a newspaper in New York from a sidewalk café in Paris”. |
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¶Houston, we’ve had a problem. April 11th marked the 50th anniversary of Apollo 13’s launch. Check out the amazing Apollo 13 in Real Time to follow the mission as it happened exactly 50 years ago (or jump to any point in the mission timeline). NASA also released Apollo 13: Home Safe, a 30 min documentary that follows the mission, and interviews Lovell, Haise, flight directors Gene Kranz and Glynn Lunney (who started his shift an hour after the notorious O2 tank explosion), and engineer Hank Rotter. Andy Saunders has enhanced images of life aboard the stricken craft. And, as usual, Scott Manley has an excellent and detailed analysis that looks at how the necessity of 50 atmospheres of pressure to keep O2 supercritical required heaters and stir fans, which required the Teflon-coated wiring inside the tank that ultimately failed. The “successful failure” of Apollo 13 remains one of the greatest all-time feats of human ingenuity and improvisation under pressure. |
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Odyssey’s service module, as seen from its command module, showing the damage to Sector 4 caused by the short-circuit and then explosion in Oxygen Tank 2. |  |
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¶News in brief. Boeing will conduct a second orbital flight test on an Atlas V in late 2020 to retest Starliner’s readiness to carry astronauts to the ISS; NASA and SpaceX practiced a Crew Dragon emergency egress via slidewire basket; Rocket Lab successfully practiced catching a parachuting rocket stage (dropped from a helicopter) with a different helicopter; Masten Space Systems won a $75.9 million NASA CLPS contract to deliver payloads to the south pole of the Moon in 2022; 2I/Borisov appears to have split into 2 pieces; in their second launch failure in less than a month, the 3rd stage of a Chinese Long March 3B failed on Thursday, causing its 5.5-ton Indonesian telecom sat to fall back into the atmosphere (historically, the Long March 3B has been a reliable booster, with 50+ successful launches); Russia suspends Soyuz production due to the pandemic—but don’t worry, they have 52 already built; the White House released an executive order reiterating the US’s rejection of the 1979 UN Moon Treaty (which has also been rejected by all other spacefaring nations, rendering it basically irrelevant) and supporting private ownership of space resources; the final first-generation Dragon Capsule left the ISS and splashed down safely into the Pacific; and, in what may mark the end of American dependence on Russia for human spaceflight, a Soyuz launched two cosmonauts and an American astronaut to the ISS (and with it astronauts may have watched White Sun of the Desert for the last time). |
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¶Etc. - A piece about Mars’ radiation environment and why spending a little time there would likely be fine, but years of settlement likely wouldn’t, without multiple meters of regolith above you. Related: the Mars Ice House was a beautiful proposal to 3D print structures on Mars out of water ice for shielding. It was followed by the Mars X-House in 2019.
- A photo of Phobos, as seen during the day from the Martian surface.
- Tantalizing evidence (paper) that the Universe’s current rate of expansion may not be spatially uniform (or that previously unknown bulk flows of matter or supercluster interactions need to be accounted for). Phil Plait has an analysis.
- The Planetary Society released a dataset of NASA investments into solar system exploration.
- NASA’s new, 3D view of methane tracks sources and movement around the globe. It’s estimated that 60% of the observed methane change is due to human activities. NASA is planning to launch GeoCarb in 2023 to provide a geostationary view of western hemisphere atmospheric methane. Meanwhile, private methane-monitoring efforts such as MethaneSAT and Bluefield are also under development.
- A second planet may have been found orbiting Proxima Centauri.
- Venus has been near its peak brightness recently, and Explaining Science lays out why this is so. (ed.: Venus, at a magnitude of about -4.5, is the third brightest object in the sky. A few weeks ago we referenced the magnitude of Starlink satellites, currently around 6.9, and due to an editing error, did not make it clear that lower magnitudes are brighter—if you didn’t know this, the article has a good explanation at the end.)
- Tory Bruno talks about rocket engines and ULA's business philosophy, focused on launching on time, every time.
- RIP John Conway, mathematician and inventor of the Game of Life.
 - NASA launches Vengeance rover to pay back Mars for killing Opportunity in 2018.
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