@grwster 😉

@martinvermeer Yeah, this is part of my “you happen to be carrying an incredible piece of scientific equipment right now” spiel in intro physics

X Window hit the big 4-0 last week!

https://www.talisman.org/x-debut.shtml

And the people on the project who suggested that relativity wasn't real and could be ignored felt like big dummies.

So they decided to just let the clock run in orbit for 20 days and see how it compared to a ground clock.

Once they were sure of the effect, a device installed on the satellite could tune the clock to tick faster or slower, in sync with ground-based clocks.

After 20 days of run time, the satellite clock was ahead of an identical ground-based clock by about 442.5 parts in 10¹². It was a lovely test of special and general relativity: less than 1% off from the predicted value!

Anyway, folks working on the project weren't entirely sure which effect would dominate.

I'm not sure why there was confusion (engineers).

And apparently there were also people involved with the project who insisted that the effects weren't real, and needn't be accounted for (retired engineers).

Calculating the fractional frequency shift of the satellite clock compared to the ground clock is a homework problem in GR textbooks.

Orbiting at 4.2 Earth radii, SR slows it down by ~ 250 parts in 10¹². The GR effect speeds it up by ~ 697 parts in 10¹².

General relativity produces the larger effect, and the orbiting clocks runs ahead of the earthbound clock by around 446 parts in 10¹². That’s an extra 38,500 nanoseconds per day.

This is a lot for GPS, which requires really precise timing.

By 1977, scientists knew that relativity would cause orbiting and ground-based clocks to beat out of sync.

Two competing effects are at work. The satellite moves rapidly in its orbit, so time dilation makes it tick more slowly compared to a ground-based clock. But clocks higher up in Earth's gravitational field should tick more rapidly than Earth-bound clocks.

Special relativity is trying to slow the satellite clock down relative to the ground, general relativity says it should tick faster.

Friends, here is a fun little physics story about satellites and relativity. It’s a day late for an #OTD, but please indulge me.

The Navigation Technology Satellite 2 (NTS-2) was launched into orbit on June 23, 1977, an early step in establishing the GPS NAVSTAR network. It was the first satellite to carry a Cesium atomic clock into orbit! 🧵

Image: Institute of Navigation

@spacegeck More like, ouro-bore-us

I guess I have different ideas about which jobs maybe shouldn't exist in the first place.

https://www.pcmag.com/news/openai-cto-mira-murati-ai-could-take-some-creative-jobs

Perfect shot.

So weird. Apple’s “quartiles” game (part of the News app) gives you the tiles to play “Juneteenth,” but won’t count it as a word. That is a weird thing to do on Juneteenth!

Sally Ride’s 1977 letter to NASA easily fits in a single post.

"To whom it may concern,

I am a PhD candidate in astrophysics at Stanford University, and am interested in the space shuttle program. Please send me the forms necessary to apply as a 'mission specialist' candidate.

Thank you,
Sally Ride”

Sally Ride became the first US woman in space #OTD in 1983.

She was one of three mission specialists aboard the Space Shuttle Challenger for STS-7. At age 32 she was also the youngest US astronaut.

Image: NASA

@wrog Maybe, but my sense is that no one clicks like an angry left-wing NYT subscriber.

It’s not “branding,” it’s just pointing out a fact. He’s a felon. There was a court case and a judge and everything.

The NYT is good on plenty of things. But their coverage of Trump always feels like it’s guided by business decisions first, and reporting second.

I actually still have a bunch of 3.5" disks (but nothing to read them with) that have all the source code, executables, drafts of the technical report, etc.

Here’s a copy of the technical report that I wrote for the project. I was told that I had to include the other names as authors for “administrative reasons.” Maddening.
https://www.osti.gov/servlets/purl/10109488

Holy smokes! I’ve known about this for a long time, but I just learned about this article that ran in the NYT while I was out of the country! They completely leave me out, and assign invention to patent holders who didn’t do the work!

https://archive.nytimes.com/www.nytimes.com/library/cyber/week/0407chaos.html