Light Years From Reality

funny-wish-stars-space

Why make a science-based meme if you’re not going to bother getting the science correct? It’s not even that hard! This is trolling, right? It has to be.

So let’s start with the first, most blisteringly obvious error. A light year is a unit of distance, not of time. I know it’s confusing because it has the word year in it, but there you go. A light year is the distance light travels through outer space in one Earth year. Light moves at about 300,000 kilometers (186,000 miles) per second, and one year is about 31.6 million seconds long, so a light year is about 9.5 TRILLION kilometers (nearly six trillion miles). To put that into perspective, Earth is just over eight light minutes from the Sun, and the icy ex-planet Pluto is about 5.5 light hours from the Sun. Go one light year out, and you’re floating in the gaping interstellar chasm, with only the occasional rogue ice-ball to keep you company.

Now let’s talk about the stars. The closest star after our own Sun is Proxima Centauri, situated about 4.3 light years away. When you look at Proxima, you’re not seeing the star as it is now; you’re seeing it as it was 4.3 years ago. If Proxima Centauri had mysteriously exploded in the last 4 years or so, we wouldn’t know about it yet.

But that’s an impossible if. For one, Proxima Centauri can’t explode; it isn’t massive enough. Even if it could, big stars go through a very visible death spiral that lasts thousands or even millions of years before they finally blow up. If Proxima were set to explode anytime in the near future, we’d know a lot about it already. Scientists can say with great confidence that Proxima Centauri has not died within the last 4.3 years. Go ahead and wish upon it if it makes you happy; the star is still alive and well.

But that’s just one star. What about all the others? Actually, they’re probably still alive as well.

EarthSky says there are between 5,000 and 10,000 stars visible to the naked eye under perfect observing conditions. Please note that this includes only stars that are individually distinguishable; if you count the band of the Milky Way Galaxy, or the distant Andromeda galaxy, you can see billions of stars in a single glance. But since they don’t appear as individual points of light, I’m saying that you cannot wish upon them.

Most of the naked-eye stars are within a radius of 2,500 light years from Earth. Given that stars live for millions or billions of years, there’s almost zero probability that any of these stars have given up the ghost, or will do so in the time it takes for their wish-granting light to reach Earth. You’re probably safe wishing on any star you can easily see. Just make sure it isn’t actually a planet. Planets do not grant wishes.

If you’re going hardcore, you can break out the telescope and potentially wish upon a star that actually has died sometime in the recent past – too recently for the light from its demise to have reached Earth, but of course you’ll have no way of knowing that.

I have one more brief point to make about wishing on stars. I have no idea how fast wishes travel, but it cannot be faster than the speed of light; ergo, even if you wish upon the nearest star, there’s a round-trip travel time of almost nine years (at least). You’ll probably have forgotten what you wished for by then, or you will have achieved it yourself through hard work and perseverance. In the remote possibility that stars are just balls of superheated plasma with no wish-granting abilities, it’s probably a good idea to keep that as a backup plan.

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