BAN #67: Church Moonrise, Photonic mea culpa
December 3, 2018 Issue #67
|Phil Plait||Dec 3, 2018|
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Pic o’ the Letter
A cool or lovely or mind-bending astronomical image/video with a short description so you can grok it
Astrophotographer Göran Strand’s images and videos have graced my blog so many times I could dedicate an entire newsletter just to list them all. Heck, just last month right here in the BAN I showed y’all a photo he took of the Moon that was just spectacular.
Getting shots of the Moon is an interesting thing: It’s easy to take some snapshots because you happen to see it in the sky, or near some foreground object. If you’re lucky it’ll turn out OK. But if you really want to capture some gorgeous ephemeral moment, something truly cool, sometimes you have to plan for it.
Göran did just that. In May, on a hike, he started thinking about a particular shot he could take of the Moon rising behind a church, and by November he was ready to get it. But there was a lot of planning that went into it, as he shows in this short and very interesting video on what it takes to get That One Incredible Photo — and trust me, the payoff is incredible:
I dabble in astrophotography; I used to be more serious, and then spent many years doing it (in a way) as a professional astronomer, but now I know that if I try to get more serious it’ll suck up all my time like a black hole. I love it, so I still do it in a limited sense… but it actually is nice to know that there are amazingly talented people out there like Göran going for these challenging shots, and achieving them in such wonderful fashion.
What I’ve recently written on the blog, ICYMI
Monday Nov. 26, 2018: Mars InSight lands on the Red Planet today! Here's how it'll happen.
Tuesday Nov. 27, 2018: An aurora glows over a (possible) rogue planet
Wednesday Nov. 28, 2018: Beginnings
Thursday Nov. 29, 2018: A distant black hole powers a colossal galactic fountain
Friday Nov. 30, 2018: Measuring all the light in the Universe. All of it. Ever.
Confession is good for the soul
It was a busy week in blogdom last week, with lots of nice news items coming out that were fun to write about. In that list of blog posts above, the last one listed (Measuring all the light in the Universe. All of it. Ever.) was particularly interesting to me. It was about a team of astronomers who used a clever method to examine the rate at which stars have been born in the Universe — as stars are born, their light interferes with light from even-more-distant galaxies, allowing them to not only calculate how many stars are born at a given time in the Universe, but how that rate has changed over time as well.
I haven’t done any research directly in this field, but there are aspects of that overlap with stuff I have done, so it naturally caught my attention. And there was an added factor: As a bonus, in principle getting the star birth rate allows you to calculate how much light these stars have emitted over the course of time, in a sense counting up all the photons that have ever left a star’s surface. The number was huge: 4 x 1084!
This is catnip to me: A solid scientific story that also has a fun hook to it involving a ridiculously huge number that makes it even more fun to write and hopefully read about. So I dove in, using that number to set up the story before diving into the real science.
[Hubble’s view of the globular cluster M53, a ball of hundreds of thousands of stars. Credit: ESA/Hubble & NASA]
But that didn’t go as planned. For one thing, I said this was all the light in the Universe ever, and that’s not really the case. It’s the light emitted by stars, and only going back about 11.6 billion years (the distance in light years to the farthest source they observed in the research). So this ignores photons from the even older cosmic microwave background (the leftover light from the Big Bang as it cooled; see here for lots more), which in fact dwarfs the number calculated for stars. As a friend of mine pointed out it also doesn’t include photons that are created and then promptly absorbed inside stars.
I should’ve been more careful. The number itself is not even mentioned in the research paper itself, but is instead only in the press release. That raised an alarm in my head, to be honest, because details on how it was calculated weren’t written out, so I had and have no idea how they actually got to that number. Mind you I’m not saying it’s wrong, just that without those details it’s easier to get tripped up explaining it. But I mitigated that worry, I told myself, by just using it as a fun diversion from the actual science that I would describe in the article.
But I got caught up in it, promoted the article that way, and then had a lot of folks question the number and how I used it — as they should have! I made a mistake. I should’ve been more careful with my word choice, and shouldn’t have devoted so much effort to that number.
Every now and again I let an idea run away with me, and sometimes it goes wrong. This was a case of that, and I apologize. My own lesson: Listen to those alarm bells when they ring.
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