Alien Sun followup

Alien Sun followup

Alien Sun followup

Bad Astronomy
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June 28 2007 2:34 PM

Alien Sun followup

There has been some interesting fallout from the Alien Sun debunking I wrote last night.

I talked to Steve Majewski, the lead author on the horribly maligned scientific paper about the Sagittarius Dwarf galaxy. He thanks me for saving him the trouble of having to debunk the claim himself. :-) He has updated his original page about all this with a disclaimer saying the Viewzone article is wrong, too.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  


But while we were talking, he pointed out that I made a mistake!

Before I go into details, let me add that the error I made does not in any way negate the facts that

1) The claim that the Sun came from a different galaxy is wrong, wrong, wrong, and 2) The Sun orbits the Milky Way smack dab along the MW's disk plane. That one fact alone kills the alien Sun claim.

What I said was that the plane of Sag Dwarf stream was perpendicular to the Galactic center. Turns out that's not right. I was basing this on a still frame from an animation based on the original data, showing the stream, the Milky Way, and the position of the Sun.


The problem was, I was seeing all that from one angle. I didn't realize it was from an animation! Dr. Majewski pointed this out, so I looked at it. If, in fact, you freeze the movie at a different spot, you get another angle on the issue:

Interestingly, from this angle, you can see that coincidentally, the stream's plane does, more or less, cut across the Galactic center. Also -- though you can't tell from the video -- the plane of the solar system, while not aligned with the stream, isn't hugely far off either from the plane of the stream, either (though not exact, of course).

However, and this is a big but, it doesn't matter. It's irrelevant. The key issue is that the Sun is well-known to orbit the MW center in the plane of the Galaxy's disk, and therefore cannot be from the dwarf.


And I have to add: while looking at the animation, it's also clear that where the stream intersects the MW disk is not right next to the Sun; it's displaced a bit. Remember, that point of intersection is what started this whole thing.

AND, something I totally forgot to add in yesterday's entry: the Sun is near that intersection point... now. But 50 million years ago (yesterday in terms of the Sun's lifetime) the Sun was 90 degrees around the Milky Way from the stream! The Sun orbits the Galactic center every 200 million years or so. That means that right now, at this particular slice of time, we're near the intersection of the dwarf's stream and the Milky Way. but in a few million years we'll be plenty far away. And over the 4.6 billion year lifetime of the Sun, we've passed in and out of that stream probably many times as the Sun has orbited the Milky Way.

So that's another reason the Viewzone claim of the alien Sun is wrong. You can't say, "Look at how close the stream is the Sun; we must be from that galaxy!" when 50 million years ago the Sun was tens of thousands of light years from the stream.


So I will happily admit I made a mistake. It was a small one, and irrelevant (though if it were a big one I'd still admit it; that's just the way I am). But in finding my own error I found two more reasons Viewzone is wrong. I wonder: will that article get retracted? Anyone wanna take bets?

Incidentally, this silliness has gotten national attention. Even Amanda Cogsdon was fooled by it (4:45 into that video). I left her a comment; we'll see if she gets back to me. :-)