Category: Space

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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.

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Full moon, mostly red except for a whiter edge at the upper left.

The evening was hectic, and I almost forgot. I had literally just put my son to bed when I remembered, “The eclipse!” We went out to see if the sky was clear.

Clouds were rushing across the sky, but for the most part, it was clear, and we had a perfect view of the moon looking like a dark brown chunk of rock in the sky.

(Then I spent 10 minutes fighting with camera settings while he went back to bed.)

Update: I went back out about an hour later to check out the view as the moon left the earth’s shadow, and caught these two photos, taken about the same time with different exposures so that you can see either the lit portion of the moon, or the part that’s still in the earth’s shadow.