Things about astronomy I wish everyone would stop believing

1.) The stars are so far away the ones you see in the night are already dead.

I once believed this, and it always sounds clever… it’s one of those counter-intuitive things we all love- like the idea that you actually catch more flies with vinegar than honey, or men with testosterone poisoning don’t have ENOUGH testosterone…  but no, this is wrong.  Space is indeed huge, but it’s not that big compared to the lives of the stars.  There are stars out there that last so long that the universe itself isn’t old enough for any of them to have died yet.

If you want math- consider: Most stars you can see with the unaided eye are within 3000 light years.  Meanwhile, even the shortest-lived stars probably last for 3 million years.  That implies that if you had 1000 of them, statistically speaking one would probably have died within the last 3000 years.  There are far more than 1000 stars visible to the unaided eye, but nearly all of them have lives measured in the hundreds of millions, if not billions of years.  Honestly?  Your best bets for a star that might actually be dead now are Betelgeuse (the red supergiant in Orion’s shoulder) and Eta Carina (the star system that’s surrounded by a giant dumbbell-shaped nebula it spat out 200 years ago when it exploded in a mysterious non-fatal way.)   Both are massive supergiant stars near the end of their short lives.  But near could still mean ten thousand years from now.

The Andromeda galaxy (2 million light years away) doesn’t really count- you can’t pick out individual stars in it without a telescope.

2.) The Sun is an average star.

Sure, stars can get 100 times more massive than the Sun, or 12 times less massive (below that they enter a never-never land between star and giant planet)… but there are EXTREMELY few massive stars, and very many low-mass stars.  Going by the RECONS data, of 259 known systems* within 10 parsecs (32.6 light years) of the Sun, only 10 are more massive than the Sun: the Sun is probably in the top 4% of all stars by mass.  4% are bigger, 96% are smaller.

The Sun is weird in other ways, too, at least for this part of the Galaxy.  Every star fuses hydrogen into helium, and is mostly comprised of those elements… but as novae and supernovae happen, the remaining gas in the Galaxy gets enriched with other elements: carbon, oxygen, nitrogen (not coincidentally the things we’re mostly made of) and so on…  Astronomers call them “metals”, and the Sun is as metal-rich as stars forming today in nearby star-forming regions.  All this, despite the Sun being 4.6 billion years older…  The best theory I’ve heard is that the Sun formed somewhere closer to the center of the galaxy where there was a higher concentration of stars, supernovae, and consequently more metals nearly 4.6 billion years ago.  Those “metals” appear to be the building blocks of planets, so that probably explains why we’re here.

3.) The Sun is yellow.

Actually, the Sun is white.  I’m not sure if we see it as yellow because we most often look at it on the horizon, or if we see it as yellow because all the blue light coming from it gets scattered out to make the sky blue.  It’s probably one of those.  In any case, the peak of the Sun’s radiation output is in green light… but given the way stars give off light, it’s also pumping out enough red and blue that we should see its combined color as white.

4.) The North Star is the brightest star in the sky.

It isn’t, that’s Sirius.  Polaris is also not constant, so Shakespeare was wrong (“I am constant as the Northern Star”)- it appears to be a kind of pulsating star called a Cepheid, which operates kind of like a lava lamp.  Polaris isn’t always the northern star, either- the Earth’s axis wobbles like a top, and back in the days the Egyptians built the pyramids, the pole was pointing toward Thuban.  Now (as in Shakespeare’s day) it’s Polaris, and some day in the far future it’ll be a star called Er Rai.  The cycle takes 26,000 years to complete, so in another 22,000 years it’ll be Thuban again.

5.) Constellations are real.

Constellations are human inventions and don’t mean anything.  One has only to look at the Chinese constellations to realize how many other ways you can divide up the stars.  And since stars are all at vastly different distances, stars that appear to be right next to each other may in reality be thousands of light years apart.  There is one interesting exception: Most of the stars in the Big Dipper are roughly 100 light years away.  They’re all about 500 million years old, have similar galactic orbits, and are probably all siblings.  Sirius (on the other side of the sky, near Orion) may also be a sibling, which would imply the Sun is passing through the middle of all this.

6.) Hubble is outside our Galaxy.

Usually, when I hear this it’s someone confusing the terms Universe, Galaxy, Constellation, and Solar System.

I wish this were true, but Hubble orbits closer than our Moon, or the satellite TV satellites.  It’s barely outside our atmosphere, much less our solar system, much less our galaxy.  The farthest humans have ever gotten from home is the far side of the Moon, on Apollo 13.  The most distant man-made object (that we can still talk to, anyway) is the Voyager 1 space probe, which is currently 120 times farther from the Sun than the Earth… which isn’t even as far out as some of the solar system objects we know about.

No, Hubble gets all its great pictures of the edge of the universe by looking outward from within our Solar System and within our Galaxy.  Even the Hubble Deep Field accidentally contains a few foreground stars in our Galaxy that were in the way of the majestic view.  Pictures claiming to be of our Galaxy are either artistic renditions or distant galaxies used as examples of what our Galaxy probably looks like.

7.) The asteroid belt is dangerously dense.

Everyone’s seen Star Wars: The Empire Strikes Back, with its asteroid field so busy that it takes excellent piloting skills to get through alive.  The idea’s shown up many times on Star Trek too, and pretty much everywhere else in science fiction.  By the 1970s, we knew of thousands of asteroids in the asteroid belt, with more being discovered daily.  However, the Pioneer 10 and 11 spacecraft passed through the asteroid belt without so much as seeing an asteroid.  We now know of over 500,000 asteroids in the asteroid belt (and more elsewhere), but still- the Galileo space probe had to be steered to a rendezvous with 243 Ida.  What I’m trying to say is that space is HUGE.  You have to WANT to find an asteroid, to find one.

Now, if we replace Star Wars’ asteroid field with a planetary ring system… then, it might work (but why not fly just above the rings and fire downwards at your enemy?  I don’t know… I leave that to the writers).  Then again, Pioneer 11, Voyager 1, and the Cassini space probe have all safely passed through Saturn’s rings (quickly), so maybe even that  isn’t good enough.

The other way to make this work would be to enter a protoplanetary system around a young star.  The problem with OUR Solar System is that, at the age of 4.6 billion years, everything that’s likely to hit something else within 4.6 billion years already has.  All we’re left with are objects on orbits that are stable for billions of years- you have your rare Shoemaker-Levy 9 events (and two more fireballs last year whose names I can’t remember) but on the whole, we’re clean out of crazy madness.  Not so in a protoplanetary system.  Objects that might collide with something in less than a million years may not have done that yet.  The asteroid field in The Empire Strikes Back was clearly in the process of smashing itself to bits- if it were in a protoplanetary system, that could have plausibly not happened yet.  Of course, the asteroid field in The Empire Strikes Back looks like it would, at most, need a few days to reduce itself to sand… but there you go.

*Actually, for reasons I won’t get into, we expect more like 400 systems within 10 pc; assuming the undiscovered ones are all smaller and dimmer than the Sun, that would make the Sun in the top 2.5% of all stars.

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