Over a billion years ago, in a distant galaxy, two massive black holes spiraled into each other.

Eight years ago, here on Earth, the resulting ripples in spacetime made some mirrors move about 1/1000 of a proton radius.

Scientists predicted this minuscule effect, then precisely measured it by bouncing lasers back and forth along the arms of a pair of 4km-long interferometers.

Gravitational waves were first detected by LIGO #OTD in 2015, 100 years after they were predicted by Einstein.

This discovery, announced the following February, marked the beginning of gravitational wave astronomy.

The description of what was discovered and how it happened fits in a short post. It is simultaneously so amazing and so preposterous that some people who hear it will want to spend the rest of their lives understanding how it could be true and what we can learn from it:

Irène Joliot-Curie was born #OTD in 1897.

She was known for her work on radioactivity, and was awarded the 1935 Nobel Prize in Chemistry for demonstrating the artificial radioactivity of stable elements bombarded with alpha particles.

I have a lot of problems with the Nobel Prize's focus on individual accomplishment, and its history of sexism. Still, it's remarkable that there's a family with three prize winners – four if you include the in-laws!

@mrecount 😀

@paulmasson 😀

Dr. Jemison was also the first astronaut to appear on an obscure late 80s-early 90s TV show called "Star Trek: The Next Generation."

@jklevasseur I will almost certainly visit DC in the next year or two, so I am adding it to my list!

Dr. Mae Jemison, the first Black woman to go into space, headed into orbit on the shuttle Endeavour #OTD in 1992.

In this photo she is being suited up before launch by Sharon McDougle.

Image: NASA

A pretty rad digital cleanup of Darlene’s 1980 World of Greyhawk map.

Image: Darlene, Robert Conley, Zach Henderson
https://batintheattic.blogspot.com/2021/12/happy-needfest-digital-darlene-greyhawk.html

Physicist Gabriele Veneziano, a central figure in the development of string theory, was born #OTD in 1942.

This photo (our coffee cups in the dish rack at the Kavli Institute for Theoretical Physics) is the closest I've come to collaborating with him.

@FirefighterGeek @briankrebs the 2

@transponderings They're all rotating the same way. The appearance of rotating in different directions is a result of capturing frames at fixed intervals while they move at slightly different speeds.

There's not too much variation in the speeds, though. Depending on whether you use polar or equatorial bands, the day varies by about 5 or 10 minutes. Another definition (used by IAU) is rotational period of the planet’s magnetosphere.

Six of the probe’s scientific instruments have been powered down. The other four will be shut off over the next few years. When it reaches a distance of one light-day we’ll still be able to communicate with it, but it won't have much to say.

Voyager 1 will remain in range of our Deep Space Network for some time after that. Eventually, though, it won't be able to muster enough power for a detectable signal, and will quietly sail off into darkness.

https://voyager.jpl.nasa.gov/downloads/
Image: NASA/JPL-Caltech

When we receive data from Voyager 1, we’re picking up a signal sent about 22 hours and 19 minutes.

Of all the objects humans have hurled into space, Voyager 1 is the closest to being one full light-day away from us.

The speed of light is 3 x 10⁸ m/s, and Voyager 1 is traveling at about 38,000 mph with respect to the Sun. A few conversions turns that into about 0.5 light-hours per year. So we're a little over three years away from Voyager 1 being one full light-day away from us.

So even though Voyager 1 has a long way to go, I wouldn't fault anyone for describing it as being at "the edge of the solar system."

It’s the fastest and most distant thing humans have ever made, it’s okay to sound a little dramatic.

But Voyager 1 hasn't left the solar system. At 161 AU, its current distance from the Sun is a fraction of Sedna's 936 AU aphelion (though it is currently further out than the minor planet).

And it's nowhere near the inner edge of the Oort cloud, thousands of AU from the sun.

This chart shows Voyager 1's location in 2013, with distance from the sun plotted on a log scale. It is at roughly the same place today, since the next step on the scale jumps from 100 to 1000 AU.

Image: NASA/JPL-Caltech

By 1998, Voyager 1 was at 68 AU, further out than Pioneer 10.

Around 2004, at about 94 AU from the Sun, it crossed the termination shock and entered the heliosheath.

And in 2012, at 121 AU from the Sun, Voyager 1 crossed the heliopause and entered interstellar space.

The frame containing Earth shows a dramatic optical artifact because we are near the Sun in the camera's field of view.

That's the Pale Blue Dot. Suspended in a sunbeam, captured from a distance of 40 AU by a probe out on the edge of darkness.

After that, mission scientists turned off Voyager 1's cameras to save power.

Image: NASA/JPL

The trajectory that gave Voyager 1 the best view of Titan (a mission priority) sent it out of the ecliptic and towards interstellar space.

Ten years later, in 1990, Carl Sagan suggested that the probe should point its camera back at the solar system for a family portrait.

The sixty frame mosaic captured by Voyager 1 on Valentine's Day of 1990 shows Jupiter, Earth, Venus, Saturn, Uranus, and Neptune.

https://voyager.jpl.nasa.gov/galleries/images-voyager-took/solar-system-portrait/

Image: NASA/JPL-Caltech

Voyager 1 discovered three new moons (Prometheus, Pandora, and Atlas) shepherding Saturn's A- and F-rings.

It also uncovered a wealth of new information about basic properties of Saturn's moon Titan, from size to atmospheric composition.

Image: NASA/JPL-Caltech