Interstellar Time & Distance

In this Sunday’s comic strip “Beetle Bailey”, the dumbest guy in Camp Swampy asks the smartest questions, and nobody knows the answers. Zero: “Boy! I’d like to visit one of those stars.” Sarge: “It would take you years to travel through space to get to one of them.” Exactly. But how long would that really take?

Beetle Bailey by Mort Walker

Happily, Wikipedia has provided in-depth answers for Beetle, Sarge and Zero. Check out these two links:

As it happens, I had been musing about the same question. I know the numbers, but can’t wrap my head around the calculations. For questions like “how long to Alpha Centauri”, I need a spreadsheet:

Interstellar distance and times

The Moon and Sun are included only to give an idea of scale here. My spreadsheet is compressed to fit on this page. Distances: Proxima Centauri 4.23, Barnard’s Star 5.96, Sirius 8.58, Gliese-581 20.3 light years.

Speeds: Earth orbital velocity is a puny 18-24,000 miles per hour. Pioneer was accelerated by Jupiter to an escape velocity of 132,000 miles per hour before leaving the solar system in 1995 — at a distance of 6.5 billion km from Earth. At that distance, its radio signal took 6 hours to reach Earth.

Scientists believe that speeds of one-one thousandth of the speed of light ( .001 c) are attainable with current technology, probably ion engines, though it would take such low-thrust propulsion systems decades to accelerate to those velocities. In the next century or so, it is thought newer technology might allow us velocities approaching .01 c.

Even so, the spreadsheet makes it crystal clear that travel to even the very closest star, Proxima Centauri, would require sending a massive vehicle with support for suspended animation or multiple generations of space travelers. At a million miles an hour, a one-way trip would take over 3,900 years; at 9.2 million miles an hour, several human lifetimes. It would take radio signals from those travelers up to 4 years to reach us, but no one alive on Earth at launch time would ever live to hear whether the mission arrived successfully. A return trip, if any, would double travel time.

Speeds of one-tenth light speed are still in the realm of science fiction. Even then, travel beyond Sirius, say a visit to the nearby Orion Nebula (1,344 light years distant), would take over 12,000 years, one way. We could pedal around the globe infinitely faster on a kiddie tricycle. It seems clear we’ll never get to cross the street or leave the neighborhood without the hyper-drives of Hollywood’s Star Wars.

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5 thoughts on “Interstellar Time & Distance

  1. Im an amatuer screenwriter – my script needs some info & it requires a meteorite to be discovered in the arizona desert & it needs the date of the event.

    SO – If a rock from a supernova in the Orion nebula landed on earth in 1991 – how long ago would the supernova have taken place? – also given the rough date of the explosion at what year in human history would the light from that explosion have been detected?

    So what I need is the length an object would take to travel from that region propelled by an average sized/powered supernova (If there is an average) & the time light takes from there is @ 1500 years – so – Im confused now – would that be the didtant past + 1500 years?.

  2. Gosh. Wish I’d put distance in light years on my article’s time and distance chart. Orion is of our closer neighbors.

    speed of light, miles per second 186284
    seconds per year 22896000
    speed of light, per year, mph 4.26516E+12
    assume distance to Orion, light years 1500
    distance, in miles 6.39774E+15
    speed of asteroid, mph 20000
    years to arrive 319,886,884,800

    At that distance the odds of hitting a grain of Sahara sand with a pea shooter would be far better. I have no idea how fast a supernova could propel a large rock but it would have to be far away to not vaporize. But supposing it was traveling 5 times as fast, 100,000 mph – that’s still 32 billion years! (Even Voyager is only traveling 8 miles per second or 28,000 mph). That implies the universe won’t even exist by the time an ordinary object coasts that far. I don’t think any large chunks of physical matter that we know of travel naturally at even 1% of the speed of light: for we humans, at least, that remains an impossibly high goal. I won’t vouch for my math or assumptions but the scales or magnitudes are on the right order of approximation, so we can skip any comparison to human history. Maybe your story should stick with the Kuiper Belt asteroids? Thanks for writing!

  3. PS – for a meteorite to be discovered in the Arizona desert, most are found by wandering around looking for suspect rocks. For anything smaller than a football, one would expect it to become covered with blowing sand in a few years, though winds could reverse and expose objects after hundreds of years, too. For a time frame, I think most discovered “strikes” would have to be geologically recent, though in theory a few few could be 1-3 billions of years old. So “the date of the event” would be whatever you as author chose, the older dates being much less plausible.

  4. PPS: Sorry I missed part of your Q, “at what year in human history would the light from that explosion have been detected?” – yes, this is where we use light years, 1,344 plus or minus 20 according to Wikipedia, for M42 the Orion Nebula. So, if there had been a supernova around 750AD, a little past the time of the final collapse of the last of ancient Rome, yes, that light would just be reaching us this century.

    My earlier point was that a rock from M42, propelled by said explosion at any credible speed toward Earth, would arrive millions or billions of years later — if at all!

    Last but not least, I updated the spreadsheet to show M42 and distances in light years. Good thing, too, because my calculations in my comment WERE off by a factor of about 6. Even so, whenever we DO attain 1% of the speed of light travel speeds, those travelers will take about 3 times longer to arrive at M42 than modern humans have existed so far.

    For those interested, check Wikipedia on ‘interstellar travel’ and then check ‘intergalactic travel’ for an even more daunting picture!

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