Earth and Moon

Leaving Solar System at the Speed Of Light

Our Solar system is big, and vast, despite it is really small compared to our galaxy, not to mention the complete universe. To put this into a perspective, you can think yourself as a photon emitted by the Sun. It takes about 8 minutes to reach the Earth after a photon has been emitted from the Sun’s surface. And it takes 5 hours to get out to Pluto from the Earth. The edge of the Solar System is far beyond the orbit of Pluto.

But, where’s the edge of the Solar System? Well, It’s complicated. Informally, the term “solar system” is often used to mean the space out to the last planet – Neptune. Some scientists thinks says the solar system goes out to the Oort Cloud, the source of the comets. The inner edge of the main part of the Oort Cloud could be as close as 1,000 AU (Astronomical Unit, the distance between the Earth and the Sun, which is around 93 million miles or 150 million kilometers) from our sun. The outer edge is estimated to be around 100,000 AU.

So, it would take around 140 hours to reach the edge of the solar system a photon emitted by the Sun, if we take the inner edge of the Oort cloud.

Solar System in logarithmic scale
Solar System in logarithmic scale. Image credit: NASA.

Before the Oort cloud, there’s a region called heliopause. The heliopause is the theoretical boundary where the Sun’s solar wind is stopped by the interstellar medium; where the solar wind’s strength is no longer great enough to push back the stellar win. The crossing of the heliopause should be signaled by a sharp drop in the temperature of charged particles, a change in the direction of the magnetic field, and an increase in the amount of galactic cosmic rays. In May 2012, Voyager 1, the farthest spacecraft from Earth as well as the farthest man-made object, detected a rapid increase in such cosmic rays (a 9% increase in a month, following a more gradual increase of 25% from Jan. 2009 to Jan. 2012), suggesting it was approaching the heliopause. In the fall of 2013, NASA announced that Voyager 1 had crossed the heliopause as of August 25, 2012. This was at a distance of 121 AU (18 billion km) from the Sun. Our photon emitted by the Sun needs around 16.5 hours to reach there.

It will take about 300 years for Voyager 1 to reach the inner edge of the Oort Cloud and possibly about 30,000 years to fly beyond it.

The 45-minute video titled “Riding Light” which showing “leaving the Solar System at the speed of light” below stops at Jupiter.

From the description of the video:

“In our terrestrial view of things, the speed of light seems incredibly fast. But as soon as you view it against the vast distances of the universe, it’s unfortunately very slow. This animation illustrates, in realtime, the journey of a photon of light emitted from the surface of the sun and traveling across a portion of the solar system, from a human perspective.”

“I’ve taken liberties with certain things like the alignment of planets and asteroids, as well as ignoring the laws of relativity concerning what a photon actually “sees” or how time is experienced at the speed of light, but overall I’ve kept the size and distances of all the objects as accurate as possible. I also decided to end the animation just past Jupiter as I wanted to keep the running length below an hour.”

Design & Animation: Alphonse Swinehart /
Music: Steve Reich “Music for 18 Musicians”
Performed by: Eighth Blackbird /

If this video would be around 100,000 years-long, it would cover entire Milky Way at the speed of light. And how big the universe is? Think of a video like that, but 13.8 billion years in length.