Category: Space

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Imagine a small village near a valley, so isolated that they just call themselves “the people.” One day they find out about another village on the other side of the valley, and they start calling them “the people across the valley.” They can keep talking about “the people,” but sometimes they need to make a distinction: right now, we’re talking about the people on *this* side of the valley, not the people on both sides.

Not incidentally, the Latin prefixes for “this side of” and “the other side of” are cis- and trans-. English uses trans more frequently, as in transport, transform, transmit, transnational etc., all of which involve something crossing a divide. Sometimes it’s quite literal, like the old terms Transjordan and Cisjordan referring to the lands on the far and near sides of the Jordan river. Or more modern terms, like the cis- and trans- forms of a molecule that can have more than one structure. Or in space exploration, translunar space (beyond the moon) and cislunar (including the moon’s orbit and Lagrange points). (Who’s that contractor for the new moon missions, again?)

Come to think of it, the moon’s another good example of the same sort of thing. When we’re just talking about life here on Earth, we can say “the moon” and it’s clear which one we mean. But if we’re talking about the whole solar system, and how Earth’s moon compares to Titan or Europa, we have to specify which one we mean.

So if we’re talking about transgender people and their experience compared to non-transgender people and their experience, the clear term to use based on English grammar is cisgender, and just as transgender is often abbreviated as just “trans,” cisgender is abbreviated as “cis.”

It’s a description, just like “acoustic guitar.” They’re still guitars, but when you need to talk specifically about non-electric guitars vs. electric ones, that’s the term we use.

“Cisgender” or “cis” isn’t a slur, no matter what Twitter’s owner thinks. It’s not casting negative judgement any more than “acoustic” is casting negative judgment against the guitar, or insisting that space on one side of the moon is better than the other.

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You wouldn’t think that books about astronomy and archaeology would have a lot in common, but Four Lost Cities (Annalee Newitz) and Under Alien Skies (Phil Plait) pack some odd similarities.

Both are about places we (mostly) can’t visit in person: Faraway planets in one case, the distant past in the other.

We have to piece together parts of the experience from what has come to us through time or through space: Telescopic observations, space probes, spectral analysis, and our understanding of physics — ruins, artifacts, aerial surveys and
what we know about people (both contemporary and in general).

For some sites we have very detailed and solid information: Angkor’s stone temples are still standing. Pompeii was well-preserved under volcanic ash and we still have first-hand writings about the city and its destruction. Mars and the moon have been extensively surveyed, including multiple landers and photographs from the surface. (And, in the case of the moon, a handful of people!)

Others require a lot of speculation: There’s a solid core of what we’ve figured out about Cahokia, but a lot of unknowns that we can sorta-kinda extrapolate from the histories and tales of surviving tribes in the area — but only to a point. Similarly, we know the rough structure of the TRAPPIST-1 solar system and some of its planets, but we have to speculate: if one of the planets in the habitable zone actually is habitable, what conditions would that require?

Both include major discoveries made within the last decade: Pluto and Charon were just a pair of dots until the New Horizons mission flew past it in 2015, bringing us pictures and measurements and so much data it took months just to download it from the probe back to Earth. Lidar surveys at Angkor in 2012 revealed the foundations of a vast metropolitan area around the temple complexes, upending our sense of how big the city was and identifying new sites to investigate.

It’s kind of funny how I read them so close together. Synchronicity and all that. They’re also both good (see also my review of Four Lost Cities and review of Under Alien Skies), and I’d definitely recommend them!

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One of many cool facts brought up in Phil Plait’s new book, Under Alien Skies is that Martian sunsets are blue!

On Earth, nitrogen scatters light randomly, with bluer colors scattering more than redder colors, so the ambient sky is blue, but when you’re looking toward the sun at a shallow angle (like sunrise or sunset), most of the blue light is scattered into the next timezone and you see red and orange.

On Mars, tiny dust particles of iron oxides (rusty dust?) reflect yellow-orange light, making the daytime sky mostly a butterscotch color…but the particles that can stay aloft in the thin atmosphere are about the size of the wavelength of blue light, so they scatter blue light forward instead of randomly. So at the shallow angles of sunset and sunrise, the sky in the direction of the sun has more blue light than the yellows that are scattered in other directions.

Essentially the same process, but reversed because of the different content of the atmosphere!

Update: I’ve finished the book, and it’s well worth reading! Here’s a link to my review!

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A photo of Venus and Jupiter close together in tonight's sky, and a close-up that appears to have very blurry images of Jupiter's moons.

Dark blue sky, blurry bushes off to the right. In the middle of the sky are two bright spots right next to each other, the right one noticeably brighter.

With rainstorms for the first half of the week, I figured the sky would be clouded over, and I completely forgot about the conjunction of Venus and Jupiter tonight.

Despite wind, rain and even hail today, it cleared up this afternoon. I happened to run out for groceries and looked up from the parking lot to see a blue sky with Venus and Jupiter right next to each other!

I snapped a quick shot with my phone. And then got out the good camera and tripod when I got home.

And…I think I may have caught some of Jupiter’s moons?!?

Closeup: two white circles against a dark blue background. The one on the right is bigger and has diffraction rays radiating from it. The one on the left doesn't, but there are two faint, blurry dots above it aligned with the disc.

The brighter planet to the right is Venus. The almost-as-bright one to the left is Jupiter. Venus shows diffraction rays, but Jupiter doesn’t…but those dots lined up on one side of it? They’re in the right location to be Callisto, Ganymede and (possibly) Io!

I’ve got to remember to use the telephoto after getting the wide shot the next time I’m taking night sky photos with planets. Just in case.

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One of the things I find fascinating about the Tunguska and Chelyabinsk impacts is that in one case it took decades of scientific research and multiple theories to settle on what probably caused it, while in the other we have video footage and the actual meteorite.

But there were eyewitnesses to Tunguska despite its remoteness, and somehow I’d never read their reports before.

As for the debate about what caused the Tunguska event: it was clearly something from space, but no one has ever found an impact crater or an actual meteorite, just damaged forest. Plus the scientific expeditions weren’t carried out until years later. Current consensus is that it was a meteor, but it exploded in the air before impact, causing the visible fireball across the sky, intense heat, shock waves, atmospheric disturbances and so on but no crater.

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Huge swaths of orange in a night sky view that wraps around the constellation Orion.
Photo by Andrew Klinger via Astronomy Picture of the Day

The first time I saw a picture of Barnard’s Loop (the arc running through Orion), I was astonished at the scale of it in the sky. I always had it in my head that (aside from the Milky Way, anyway), most of the astronomical features we see in photos are not just too faint but too small to see with the naked eye. The fact that I could instantly see the scale, because it wraps through a constellation I know, really drove home the fact that a lot of features don’t need telescopes, just long exposures. (And the right film/sensors and filters.)

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An orange ring in the blackness of space

How cool is it that we now have an actual image of the event horizon of a black hole! More precisely: it’s the glowing accretion disc of matter falling into the black hole, and the event horizon’s silhouette.

The Event Horizon Telescope, actually a worldwide array of telescopes, used interferometry to effectively create a planet-sized telescope to see the light around the supermassive black hole at the center of M87, a galaxy 55 million light years away.

I remember talking with a college classmate about giant interferometry telescopes back in the late 1990s. It’s incredible to see the technique actually making discoveries like this!

What we’re seeing in this image isn’t a top-down view of the accretion disc, but an angled one — think of Saturn’s rings — and the gravity of the black hole is bending the light from the disc. Phil Plait has a great article on the science behind the image. Katie Mack has a Twitter thread on how the image was produced, why the ring looks the way it does (it tells us which direction the disc is spinning!), plus simulations of this type of black hole seen from different viewing angles.

Here’s a paper talking about the history of black hole images, with a detailed discussion of what you should expect for the “shadow” image we’ve just seen. Check Fig 12, with renderings of shadows for disks at different angles arxiv.org

4x4 grid of black circles with red/yellow outlines, with bright and dark spots in the outlines.

— Katie Mack (@AstroKatie) April 10, 2019

Direct links to the articles she mentions:

And this Mastodon thread by @SohKamYung@mstdn.io collects some more articles worth checking out:

Forbes makes the excellent point that, while we’d seen a lot of circumstantial evidence for black holes over the last few decades, this confirms that they exist.