Oops! Wrong Galaxy!

[RCNelson]

Oops! Wrong Galaxy!

In the latest commentary (http://www.randi.org/jr/2007-04/042707chop.html#i8), Randi wrote:
The NBC-Today Show last week got all excited over a news item from the astronomy world that a planet has been discovered with very Earth-like features, in another galaxy, and even showed a photo of the object, though, since it could hardly be more than a few pixels in size, that image was an imaginary guess. ... You see, this planet they were rhapsodizing over is 20 light-years away from us.

Ummmm... 20 light-years away from us is still in the same old Milky Way galaxy as us. In fact, 20 light-years away is in our close stellar neighborhood.

[sphenisc]

The "Independent" newspaper had a similar error on its Letters page - a lot of people seem to confuse "extrasolar" with "intergalactic".

[jeffq]

I cringed when I read Randi's error. Anyone with even a modest interest in astronomy should know in his or her bones that galaxies are far, far larger than 20 light years. I remember from childhood (in the '60s) that the Milky Way galaxy is commonly considered to be 100,000 light-years wide (although I gather this is only a rough approximation).

I thought perhaps that Randi might have confused the distances in this news item (switching between tens of light-years and trillions of miles) with another recently announced astronomical spectacle that is indeed outside our galaxy and involves millions of light-years. Many science and some general-interest news outlets reported last week that an enormous plasma cloud, 6 million light-years wide (more than twice the distance between the Milky Way and Andromeda galaxies), is believed to be the "exhalation" of super-massive black holes and may be a (the?) source of cosmic rays. It's located in the Coma Cluster, which is something like 300 million light-years distant; i.e., definitely extragalactic. Space.com (http://www.space.com/scienceastronomy/070420_plasma_cloud.html) has a good article on this intriguing, galaxy-dwarfing object.

[BillyJoe]

I cringed when I read Randi's error....galaxies are far, far larger than 20 light years....the Milky Way galaxy is commonly considered to be 100,000 light-years wide .


I can get to intergalactic space by travelling only 950 light years. ;)

[ImaginalDisc]

The "Independent" newspaper had a similar error on its Letters page - a lot of people seem to confuse "extrasolar" with "intergalactic".

Intergalactic /= planetary.
Planetary /= intergalactic.
Another dimension. Another dimension. (http://www.youtube.com/watch?v=GDS83yrM30Y)

[jeffq]

I can get to intergalactic space by travelling only 950 light years.

Well, sure, the Z-axis of the Milky Way is only about 1,000 light-years outside the Core, which should mean that you could get into intergalactic space in at most half of that. (I'm not sure where "950" comes from, except maybe to be sure that you're well beyond the galaxy.) But:


An object within 20 light-years of anything considered to be within our galaxy (like our solar system) couldn't be considered extra-galactic. The galaxy doesn't have a hard border from which we could say an object was only 20 LY outside it (too small to exceed error margin).

If there was something 6 million LY wide only 20 LY "outside" our galaxy, it would look more like the Milky Way and other Local Group objects were appendages of it, sort of like the hexagonal patterns on the outside of a soccer ball compared to the ball itself. (Pardon my Americanism.)


In any case, 20 light-years cannot represent a meaningful "extragalactic" distance, even if our Sun were on the "border".

[JoeTheJuggler]

I know--he meant "in another galaxy" the way astrologers say that a planet is "in" a zodiac constellation.

OK maybe it was a boo boo.

[Dr Aardwolf]

Maybe Randi should have checked with the Badastronomer first?

There are worse mistakes out there. I read today on MSN that it would take 5 billion years to reach Gleise 581, which would mean travelling at less than the escape velocity of Earth (40,000 kilometres per hour) In other words, impossible. At escape velocity it would take about 600,000 years to reach Gleise 581.

I wrote them that this must be an estimate by Richard Branson, as Virgin Galactic would probably leave astronauts in the depature lounge for 4.5 billion years!

[BillyJoe]

Well, sure, the Z-axis of the Milky Way is only about 1,000 light-years outside the Core, which should mean that you could get into intergalactic space in at most half of that. (I'm not sure where "950" comes from, except maybe to be sure that you're well beyond the galaxy.) .


The Milky Way Galaxy is a disc 100,000 light years across, but only 2,000 light years thick. This means it extends 1000 light years to either side of the galactic plane. The Earth lies 50 light years above the galactic plane. Therefore it is 950 light years to intergalactic space.

[Grimoire]

The Milky Way Galaxy is a disc 100,000 light years across, but only 2,000 light years thick. This means it extends 1000 light years to either side of the galactic plane. The Earth lies 50 light years above the galactic plane. Therefore it is 950 light years to intergalactic space.

Obligatory Monty Python quote. (http://www.geocities.com/fang_club/galaxy_song.html).

[tracer]

There are worse mistakes out there. I read today on MSN that it would take 5 billion years to reach Gleise 581, which would mean travelling at less than the escape velocity of Earth (40,000 kilometres per hour) In other words, impossible. At escape velocity it would take about 600,000 years to reach Gleise 581.
Not impossible.

When a space probe achieves Earth escape velocity, it means has enough kinetic energy that it will still be travelling away from the Earth at a theoretically infinite distance. This does not mean it doesn't slow down as it pulls away from the Earth. Earth's gravity is still going to be slowing it down as its distance from the Earth increases, albeit the effect will be less and less the farther it gets away.

An object with exactly Earth escape velocity will, in a universe containing only that object and the Earth, be at a dead stop at infinite distance.

[tracer]

Ummmm... 20 light-years away from us is still in the same old Milky Way galaxy as us. In fact, 20 light-years away is in our close stellar neighborhood.
Since the time this post was written, the first sentence of that SWIFT article section has been revised to read:

"The NBC-Today Show last week got all excited over a news item from the astronomy world that a planet has been discovered with very Earth-like features, in our own galaxy, and even showed a photo of the object, though, since it could hardly be more than a few pixels in size, that image was an imaginary guess.."

[jeffq]

...the Z-axis of the Milky Way is only about 1,000 light-years outside the Core...

The Milky Way Galaxy is a disc 100,000 light years across, but only 2,000 light years thick. This means it extends 1000 light years to either side of the galactic plane. The Earth lies 50 light years above the galactic plane. Therefore it is 950 light years to intergalactic space.

Interesting difference of opinion here. I got my number from Wikipedia's article on Milky Way, which is usually pretty good about dry scientific information. But digging a little deeper, I found that WP didn't have a citation for that specific figure. A little web searching turned up thickness values from 1,000 to 10,000 LY. My old college astronomy textbook claims 3300 LY (1000 parsecs) from Sol to the galactic edge along the Z axis. The only reference I found (so far) for 950 light-years was "A Tour Through the Milky Way" (http://www.stdimension.org/int/Cartography/mwtour.htm) from Star Trek Cartography. It would be rather amusing if they got it right. What is your source, BillyJoe? (I've also asked for sources at Wikipedia. I'd really like to nail this down.)

[Metullus]

Interesting difference of opinion here. I got my number from Wikipedia's article on Milky Way, which is usually pretty good about dry scientific information. But digging a little deeper, I found that WP didn't have a citation for that specific figure. A little web searching turned up thickness values from 1,000 to 10,000 LY. My old college astronomy textbook claims 3300 LY (1000 parsecs) from Sol to the galactic edge along the Z axis. The only reference I found (so far) for 950 light-years was "A Tour Through the Milky Way" (http://www.stdimension.org/int/Cartography/mwtour.htm) from Star Trek Cartography. It would be rather amusing if they got it right. What is your source, BillyJoe? (I've also asked for sources at Wikipedia. I'd really like to nail this down.)I tried MapQuest.com. It did not help.

[The Bad Astronomer]

The disc of the Galaxy is not well-defined. Some kinds of stars (more massive) tend to stick closer to the gravitational median of the Galaxy, while others, like red dwarfs, "puff out" more from the center. So the thickness of the disk can depend on what kind of star you're looking at.

I am constantly amazed in astronomy that things are rarely ever simple, with a single, isolated answer. Almost everything has underlying, more subtle things affecting them.

[BillyJoe]

Interesting difference of opinion here. I got my number from Wikipedia's article on Milky Way, which is usually pretty good about dry scientific information. But digging a little deeper, I found that WP didn't have a citation for that specific figure. A little web searching turned up thickness values from 1,000 to 10,000 LY. My old college astronomy textbook claims 3300 LY (1000 parsecs) from Sol to the galactic edge along the Z axis. The only reference I found (so far) for 950 light-years was "A Tour Through the Milky Way" (http://www.stdimension.org/int/Cartography/mwtour.htm) from Star Trek Cartography. It would be rather amusing if they got it right. What is your source, BillyJoe?


Fortunately, not from Star Trek Cartography :D

http://scienceworld.wolfram.com/astronomy/MilkyWayGalaxy.html


...The Galaxy's dimensions are 100,000 ly in diameter and 2,000 ly thick
thick. According to three recent independent studies, the Sun lies ~50 ly north of the galactic plane...


Of course, the thickness must vary, being thickest at the centre and thinner at the edge. The Earth is situated about 3/5 out from the centre of the galaxy. So, if 2,000 ly is an average, it is perhaps slightly less than that where the Earth is situated
.

[Jeff Corey]

The disc of the Galaxy is not well-defined. Some kinds of stars (more massive) tend to stick closer to the gravitational median of the Galaxy, while others, like red dwarfs, "puff out" more from the center. So the thickness of the disk can depend on what kind of star you're looking at.

I am constantly amazed in astronomy that things are rarely ever simple, with a single, isolated answer. Almost everything has underlying, more subtle things affecting them.

Try being an experimental psychologist. And we even have the luxury of doing experiments.

[BillyJoe]

I am constantly amazed in astronomy that things are rarely ever simple, with a single, isolated answer. Almost everything has underlying, more subtle things affecting them.


Evasion noted. :D

[T'ai Chi]

"in another galaxy" has been changed to "in our own galaxy", lol

Again, quoting the Weekly Rant (ie. Commentary):


The NBC-Today Show last week got all excited over a news item from the astronomy world that a planet has been discovered with very Earth-like features, in our own galaxy, and even showed a photo of the object, though, since it could hardly be more than a few pixels in size, that image was an imaginary guess..


Such things are done all the time in astronomy-related science news. I'd like to get some stats on the number of photos in such pieces that have 'artist's rendition' under them.

[fsol]

Intergalactic /= planetary.
Planetary /= intergalactic.
Another dimension. Another dimension. (http://www.youtube.com/watch?v=GDS83yrM30Y)

ha! I was going to link that when I started reading your post. :)