- The speed of light in a vacuum is about 186,282 miles per second (299,792 kilometers per second).
- A scientist at NASA animated how long it takes light to travel around Earth, as well as between the planet, its moon, and Mars.
- The physics animations show just how fast (and slow) the speed limit of the universe can be.
A series of new animations by a NASA scientist show just how zippy – and also how tortuously slow – the speed of light can be.
Light speed is the fastest that any material object can travel through space. That is, of course, barring the existence of theoretical shortcuts in the fabric of space called wormholes (and the ability to go through them without being destroyed).
In a perfectly empty vacuum, a particle of light, which is called a photon, can travel 186,282 miles per second (299,792 kilometers per second), or about 670.6 million mph (1.079 billion kilometers per hour).
This is incredibly fast. However, light speed can be frustratingly slow if you’re trying to communicate with or reach other planets, especially any worlds beyond our solar system.
To depict the speed limit of the cosmos in a way anyone could understand, James O’Donoghue, a planetary scientist at NASA’s Goddard Space Flight Center, took it upon himself to animate it.
“My animations were made to show as instantly as possible the whole context of what I’m trying to convey,” O’Donoghue told Business Insider via Twitter. “When I revised for my exams, I used to draw complex concepts out by hand just to truly understand, so that’s what I’m doing here.”
O’Donoghue said he only recently learned how to create these animations – his first were for a NASA news release about Saturn’s vanishing rings. After that, he moved on to animating other difficult-to-grasp space concepts, including a video illustrating the rotation speeds and sizes of the planets. He said that one “garnered millions of views” when he posted it on Twitter.
O’Donoghue’s latest effort looks at three different light-speed scenarios to convey how fast (and how painfully slow) photons can be.
How fast light travels relative to Earth
One of O’Donoghue’s first animations shows how fast light moves in relation to Earth.
Earth is 24,901 miles around at its center. If our world had no atmosphere (air refracts and slows down light a little bit), a photon skimming along its surface could lap the equator nearly 7.5 times every second.
In this depiction, the speed of light seems pretty fast – though the movie also shows how finite it is.
How fast light travels between Earth and the moon
A second animation by O’Donoghue takes a big step back from Earth to include the moon.
On average, there is about 238,855 miles (384,400 kilometers) of distance between our planet and its large natural satellite.
This means all moonlight we see is 1.255 seconds old, and a round-trip between the Earth and moon at light speed takes about 2.51 seconds.
This timing is growing every day, however, as the moon is drifting farther from Earth at a rate of about 1.5 inches (3.8 centimeters) per year. (The moon is constantly sapping Earth’s rotational energy via ocean tides, boosting its orbit to a greater and greater distance.)
How fast light travels between Earth and Mars
O’Donoghue’s third speed-of-light animation illustrates the challenge that many planetary scientists deal with on a daily basis.
When NASA tries to talk to or download data from a spacecraft, such as the InSight probe on Mars, it can do so only at the speed of light. This is much too slow to operate a spacecraft in “live mode” as you would a remote-controlled car. So, commands must be carefully thought out, prepackaged, and aimed at the precise location in space at the precise time so that they don’t miss their target.
The fastest a conversation could ever happen between Earth and Mars is when the planets are at their nearest point to one another, an event called closest approach that happens once roughly every two years. On average, that best-case-scenario distance is about 33.9 million miles (54.6 million kilometers).
As that 60-second clip of O’Donoghue’s full movie on YouTube shows, light takes 3 minutes 2 seconds to travel between Earth and Mars at closest approach. That’s six minutes and four seconds for a light-speed round-trip.
But on average, Mars is about 158 million miles from Earth – so the average round-trip communication takes about 28 minutes and 12 seconds.
The speed of light gets more depressing the farther you go
The hurdle of light’s finite speed gets even more challenging for spacecraft such as New Horizons, which is now more than 4 billion miles from Earth, and the Voyager 1 and 2 spacecraft, each of which have reached the space between stars.
The situation gets downright depressing when you start looking outside the solar system. The closest-known exoplanet, called Proxima b, is about 4.2 light-years away from us (a distance of about 24.7 trillion miles or 39.7 trillion kilometers).
However, the fastest any spacecraft has ever gone is NASA’s Parker Solar Probe at about 213,200 mph; at that speed, it’d take 13,211 years to reach Proxima b.
A Russian-American billionaire’s Breakthrough Starshot project envisions a way to address this speed problem. The multidecade plan is to build and fly tiny “nanocraft” past such exoplanets via ultrapowerful laser blasts, ideally at a planned cruise velocity of 20% of the speed of light. Yet the entire concept is still theoretical, may end up not working, and would operate at a fraction of light-speed.
Space is impossibly vast. Although the universe is about 13.77 billion years old, its edge is about 45.34 billion light-years away in any direction and is increasing due to expansion.
That’s far too big to illustrate in a simple animation. One illustration comes close, though: this image created by musician Pablo Carlos Budassi, which combines logarithmic maps of the universe from Princeton and images from NASA to capture it all in one picture.
This story has been updated.