When you look up at the sky at night, the velvet vault seems peppered with thousands of stars. But how much of the Galaxy are we really seeing? Just how far away is the farthest star you can see? What about the farthest object?
Q & BA Episode 3: "The Farthest Star" is now online. Here are your viewing options:
- Watch it here as an embedded YouTube video. (Note: I originally had this as a Gooogle video, but the audio and video weren’t synched for some reason. In the file I uploaded they were fine. I tried to re-upload a different file, and the same thing happened, so I have replaced the Google embed with the YouTube one). [Later note: I uploaded a new video to Google and it's fine now. There is a link to it below].
- Go to Google video to watch it (note: updated with a new version where the audio and video match)
- Go to YouTube (Another note: It took YouTube over 12 hours to get the video processed, and that was only after I had to upload it twice! YouTube is teh suck.
- LibSyn (video)
- LibSyn (audio)
I am also trying something new. The ITPC protocol supposedly lets you automatically subscribe to a podcast via iTunes. Here is that link. It worked for me when I tried it, but your mileage kilometerage may vary. If you click on it, tell me in the comments what happened. Unless your machine melts. Then it’s Apple’s fault.
Show notes
The question asked was, "How much of the Milky Way Galaxy do we see with the naked eye?", asked by Richard Saunders. Full disclosure: Richard is a dear friend, but his question was so good I decided to use it despite any possible accusations of cronyism.
For more info about stars, get yerself over to Jim Kaler’s site. He’s one of the nicest guys in astronomy, and his site is pretty cool.
Image pedigrees:
Deneb and Mu Cephei from Davide De Martin’s Sky Factory
Small star next to Sun: NASA/Walt Feimer
Star sizes (for giants): Wikipedia
Keck Observatory: JPL/NASA
GRB 990123: NASA/STScI/Andy Fruchter
M81: NASA/JPL-Caltech
Jupiter orbit: I did that one myself, using The Sky planetarium software.
Orion/Rigel: I had that image lying around at work for an educational activity we developed, and I had permission from the photographer, but danged if I can find it now. Pretty though, isn’t it?
Minties: the best candy lolly in the whole wide world. Yummy. Those are courtesy of many Aussie friends who keep me supplied. Thanks!
February 19th, 2007 at 1:32 am
Very nice. These little segments are definitely getting better with each one, and will no doubt continue to get better. If you don’t mind, though, I’d like to throw a little advice out for you as someone who’s worked in TV.
First, speak slower. Particularly when making a joke. You tend to talk very fast, particularly when excited (as you no doubt are talking about these things 8^) ), and even more so when you insert a quick little joke. The jokes are fine, but talking so fast just isn’t good. Trust me on this.
The background you choose actually works out pretty well. A lot of people would try and go for a very plain backrground, which is boring. It has depth to it, which is good, but at the same time it isn’t distracting. Also, because you stand right in front of a corner, the lines all naturally draw the eye to your face, which is good.
Also, your might want to use more graphics instead of a model. For example, the model of the milky way should probably go. When emphasizing extreme differences in size, though, you’re probably OK with doing things like the candy. That’s probably about the only time you’d want to do that, though.
As for the actual subject matter, just like in all your other work, you do it very well. It’s informative and, just as importantly, not boring. You’re energetic, which is a good thing, and you come across as being enthusiastic about your subject matter. Being animated is also a good thing, though don’t do it in excess.
Above all, slow down the talking.
Keep up the good work! I love your blog and your website, so take the above very much as constructive criticism. Study some Bill Nye clips to see how he does it when doing monolouges. That’s probably the direction you want to go.
Again, keep up the good work!
February 19th, 2007 at 1:54 am
Phil, you are an inspiration. I will never forget that time we were in Canberra when you showed me The Belt of Venus – It (to quote Brain Brushwood) ‘blew my freaking mind!’ Can’t wait until the Amazing Adventure.
February 19th, 2007 at 2:04 am
Good one, but I don’t think you answered the initial question “how much of the Galaxy are we really seeing?” We can’t see many of the individual stars except when really close or really big, but what is it we do see, and how much of the galaxy does it make up? We can obviously see some things that aren’t individual stars, or else we wouldn’t see other galaxies, but what is it? Glowing dust/gas/golf balls? The light of a billion stars all blured out by the eyes limitations? The FSMs nightlight?
February 19th, 2007 at 3:49 am
Out of interest Phil, why have you chosen M4A files for the audio-only version rather than MP3? Is it possible to add the show notes to the LibSyn page too (or perhaps a link from there to this page)?
February 19th, 2007 at 4:46 am
BA: Question: can you put a link on the left hand tool bar to a page that has the links to all of these Q&BAs on them? I didn’t watch the first one, and now I have to try and sift if out from your regular blog. That isn’t a big deal right now, but when there are 15 Q&BAs, or 100, spread over 5 years it won’t be so easy;).
(or does such a link already exist and I just can’t find it?)
February 19th, 2007 at 5:44 am
I am soooo confused
The galaxy is 100, 000 light years across
the sun is in the center and you said 25,000 light years
You said 100,000 light years across – 25,000 to the center….
and you are showing this on a CD Model
If the diameter is 100,000 then shouldn’t the radius (center to the edge) be 50,000
Or is space geometry different?
Thanks for a great podcast series. I can learn just enough astronomy to feel enlightened without being being buried in so much technojargon that my brain hurts.
PS. The Itunes feed work nicely.
February 19th, 2007 at 5:45 am
I’ve been a casual BA reader and fan for a few years now, but since the Q&BA segments have appeared, I’ve been hooked!
This episode in particular was absolutely fascinating to me and inspired my curiosity to do a bit more research on gamma-ray bursts.
Thanks Phil, and keep up the good work!
February 19th, 2007 at 5:49 am
Lee, what I believe Phil meant was that the Sun is halfway between the CENTER of the Milky Way, and the OUTER EDGE.
Since the distance from the outer edge to the center is around 50,000 ly, the distance from the outer edge to the halfway mark (en route to the center) is 25,000 ly.
February 19th, 2007 at 6:12 am
Re “kilometerage”: I’ve tried using the work “clickage” here in Canada since people I grew up with refered to kilometers as “clicks” (stemming from watching an odometer). Hasn’t really caught on, but I still use it anyway.
February 19th, 2007 at 6:24 am
“Clickage” hehehe awesome. I’m going to try using that too. Maybe if enough of us do it it will catch on and we can stop using mileage.
February 19th, 2007 at 6:25 am
I love these segments! It is a joy to watch someone who obviously cares a lot about the subject.
Keep up the good work. I’ll work on finding a good question to submit..
February 19th, 2007 at 7:11 am
Awesome ep…gr8 work…i thin ku should start to debunk Bad Astronomy thru video too…
February 19th, 2007 at 8:02 am
The youtube copy sees to be marked “private”…. I’ll check out the other version
February 19th, 2007 at 8:09 am
So I’m curious, have astromers “mapped” the locations of all the stars of the Milky Way?
OEJ
February 19th, 2007 at 9:05 am
“Kilometerage”: in Québec, we really say “kilométrage”. But we also occasionally hear “milage”.
February 19th, 2007 at 10:37 am
You’re my hero.
So what was sitting on the shelf this week? Is it another book, or just a picture? I like the pictures, props, and little diagrams that you use to explain your topic. They really are effective. The Milky Way made out of cds and a rubber ball makes me smile every time I see it.
February 19th, 2007 at 11:15 am
I agree with Bjornar, you did not answer the question. How much (what percentage) of the milky way is visible in the night sky?
February 19th, 2007 at 11:27 am
First, thanks for all the comments!
arcraig: I’ve slowed my talking speed considerably for this vidcast, but if I slow it any more the length will be too long! I’m trying to speak at a normal conversational speed.
Bjornar, YinYang0564: I did answer it! I said we can see out about 60-100 light years, while the Galaxy is 100,000 light years across. I say this specifically at 1:24 into the video.
lee: Cal is correct. We are 25,000 light years out from the center of the Galaxy, or half the radius. Remember, it’s 100,000 light years all the way across, so it’s 50,000 from the center to the edge, and we’re halfway between them.
Lauren: It’s a box for my plastic model kit of the Eagle transporter from "Space:1999".
February 19th, 2007 at 11:49 am
BA – arcraig is probably technically correct about the superiority of graphics over models, but I like your little milky way CD. (Then again, I loved the tacky special effects on the original Dr Who and nothing beats the BBC props department’s work on “Are you being served?”
But maybe a good low-tech pointer (a sharp pencil) would be good to point out features and locations. I knew where the Sun should be on the MW model, but its easy to see how Lee got confused. A finger is just too big a pointer, and its hard to remember to hold it still for long enough.
Also, I agree with Bjørnar that you really didn’t answer the original question. Doing the math for Mu Cephei (was that the right star?) which is easily visible but not very bright to the naked eye and is 2,500 to 5,000 ly which is only 10 to 20% of the distance to the edge or center. It doesn’t make much sense to talk about “aversage bright stars” since we are talking about the upper exteme of a bell curve (most likely) of star brightnesses, but there are a handful of bright stars in the range of 1000 to 1500 lightyears and most visible stars are much closer than that, so the stars we are seeing are only a tiny fraction of the galaxy.
The diffuse glow of the Milky Way resolves into thousands of stars (still embedded in a dimmer diffuse glow) with binoculars or a very small telescope. Galileo’s telescope, which I think was only about 1″ aperture and was terrible by modern or even department store standards, could do this. Since these stars are probably about 2-3 magnitudes fainter, they are about 2-4 times as far away, still only a small fraction of the Milky Way’s size.
I’m not sure how far into the milky way we can see with a large telescope before the view gets blocked by dust clouds, various nebulae and the glare of closer stars, but M24 is actually a patch of an inner milky way spiral arm visible through a chance hole in the nearer clouds. It is about 10,000 ly, or less than 1/2 way to the center, and is probably the most distant bit of the galaxy that can be seen in visible light (excluding globular clusters, halo stars, satellite galaxies, etc.) unless there are other such holes. See
February 19th, 2007 at 11:53 am
It ate my URL for M24… trying again: http://www.seds.org/messier/m/m024.html
February 19th, 2007 at 12:16 pm
While most of the stars are “dinky dim bulbs” very few of these red dwarf stars are visible to the unaided eye. In fact, the closest star (Proxima Centauri @ 4.2 LY) is beyond the reach of 50mm binoculars (11th magnitude). Almost all naked eye main sequence stars are at least as luminous as the Sun.
February 19th, 2007 at 12:20 pm
First time I’ve looked at one of the videos – nice job, Phil. Slowing down a bit more would be good, although that cuts down on the content you can stuff into a 5-6 minute video as you’ve pointed out. The other thing I would urge you to do is hold the images a tad longer. They seemed to cut off a second before I was ready.
The item that really got me was Mu Cephei. Not only is it huge, but it’s diffuse. “Only” twenty solar masses with a radius bigger than the orbit of Jupiter! I wonder what the pressure/density would be at various depths, such as the equivalent of Earth’s orbit?
February 19th, 2007 at 12:47 pm
“…most of the stars you see are these dim bulbs pretty close by…”
Which I’m taking to mean that Phil lives near Hollywood.
(Thank you, thank you, I’m here all week).
Arrgh! That WAS an Eagle model in the background! Well, okay, the box for one. Haven’t seen one of those for decades. And probably wouldn’t pay the price they’d be asking now anyway…
But I think Phil needs an ISS model in the background.
February 19th, 2007 at 12:48 pm
Buzz, the question specifically was what we could see with the naked eye. Remember, too, that I want to keep these to about 5 minutes, which is really not a whole lot of time to go into details — there is no “average” star, but I have to make concessions. I thought about talking about the diffuse MW glow, but simply didn’t have the time. I’m still feeling my way through these, but I might cut back a bit on the tangents and just stick more literally to the question asked.
February 19th, 2007 at 1:49 pm
That YouTube thing has happened with just about every video I’ve uploaded–it appears, then disappears for awhile, then it’s back. It’s almost like Acme Disappearing-Reappearing Ink.
Whereas, Google Video has the sound out-of-sync in almost everything I’ve uploaded. The only way I’ve fixed it is to load it into QuickTime (the pay version) and save it as a .mov, then upload it. I don’t know why.
And I like the models! But then again, I’m a Doctor Who fan, too…
Keep up the good work!
February 19th, 2007 at 2:06 pm
Just wanted to throw out there that CNN Headline News is predicting the end of humanity due to asteroid collision in 2036. despite aknowledging that preliminary calculations show a 1 in 45,000 chance of collision, the anchor reads that it’s “headed straight for Earth.” He also refers to the asteroid as “the astronaut” once, too.
February 19th, 2007 at 2:53 pm
As an engineer, I would just like to say that you do us dorks proud Phil. If I showed this to my wife, she would laugh for the entire 5 minutes. Apparently she thinks I get like this when describing fracture mechanics, flutter, vibrations, fluid dynamics, etc. That crazed look appears in my eye, I talk at warp speed, and I keep explaining even as she tries to escape. Keep up the good work!
February 19th, 2007 at 3:23 pm
Keep your own style Phil, I think its great you are so animated about the subject. Using common items as props shows you are a true teacher. Outstanding job, and looking forward to many, many more.
February 19th, 2007 at 4:10 pm
So much for youtube: It says now “This video has been removed by the user.”. They got some serious problems at the moment.
Good thing i watched the video elsewhere. What can i say? I love it
February 19th, 2007 at 4:17 pm
So, I have taken to showing my grade 8 class your clips on monday mornings as it melds well with science course and, well, I dig’em. So much, in fact, that I feared this morning as I was preparing for the little ones to enter and get primed for their “monday morning science media”I cast doubt upon myself, thinking :” do they even like this stuff?!?”
Then, as they sat there patiently and waited for me to deal with the Mac’s at my school (in my opinion, glorified Commodor 64…that’ll get some retorts, I am sure) and your youtube freeze frame came up I heard, in stereo, “sweet…its the bad astronomy guy…” and papers rustled and got ready to watch.
They sit speechless for your bits. Grade 8′s and I together in a moment of BA bliss.
Thanks Phil, I found your book in a random book shop in Taiwan years past as I was serching for english books, and picked it up with interest only to find I had no money on me. I travelled 3 hours back to that book store to get it a few weeks later, never knowing that it would lead me to teaching classes with your presence. You done good.And I thank you. Both my brother in law and father have been overly pleased with your books (I gave them as gifts…the bookstore was curious why I wanted two of the same books….).So, again. Good job.
February 19th, 2007 at 4:27 pm
Ivan: the YouTube links are fixed. I re-uploaded it, removed the old version, but then forgot to update the link in my post. D’oh!
Mokey: wow. Just, wow. Thanks. You made my whole week!
February 19th, 2007 at 4:34 pm
You know Phil, the title to this entry reminds me of an episode of Star Trek: The Animated Series. Do you know what I speak of?
Anyway, around here a lot of the faint stars are lost to light pollution. I don’t even think that Andromeda is visible. So, I get a truncated view of the galaxy.
February 19th, 2007 at 4:41 pm
How far would our own Sun have to be away from Earth so that we could no longer see it with the naked eye?
Or, 93,000,000 miles times X= Sun is invisible
What is the answer to “X” ?
Thanks
February 19th, 2007 at 6:49 pm
Thanks! Your videos are just great. I send them to my friends, some of whom are science types and they all really dig them. One thought occurred while watching: when I look at the Andromeda galaxy with the naked eye or through binoculars, am I seeing the cumulative effect of many stars, any single one of which at that staggering distance would be invisible?
P.S. – if one knows exactly where to look, the Andromeda galaxy can be glimpsed, even with moderate light pollution. (Though dark skies way out in the country are best.)
February 19th, 2007 at 8:25 pm
The show is great! However, would it be possible to have separate feeds for audio and video podcasts? iTunes downloads the last one -often, audio- but I just want the videos.
February 19th, 2007 at 8:37 pm
These videos rock,
I hope to see the model galaxy show up in other Q&BA segments no need to go crazy with the video editing if a low tech solution works. Keep them coming.
February 19th, 2007 at 10:46 pm
It left me a tad confused, too. Are most of the objects visible to the naked eye within 60 light years distant?
Otherwise, I like these segments. It’d be great if they were PSAs to teach kids on TV…
Thank you,
Jonathan
February 19th, 2007 at 11:26 pm
[...] ¿Cuál es la estrella más lejana que podemos ver a simple vista? (en inglés)Phil Plait, de Bad Astronomy Blog, responde en la tercera entrega de su video-podcast de preguntas y respuestas de astronomÃa. [...]
February 19th, 2007 at 11:31 pm
Dr. Plait, I don’t know if you’ve seen this already, but it seemed to go along with your discussion in this Q & BA: on my weblog, I recently posted an animation I came across purporting to show the relative sizes of planets and stars. I thought it was quite well done!
February 20th, 2007 at 1:06 am
I’ll echo the comment by rvr about iTunes only downloading the last feed item i.e. audio. I too would like the video rather than the audio as I have yet to see this model that everyone is talking about. Of course, I could manually download the video in iTunes or watch it from here
February 20th, 2007 at 4:22 am
@Darmok: That’s just… Wow… I feel really small now..
@Phil: You talked about the Sun “burning up” 5 million tons of mass a second in Q&BA ep. 2. How does that compare to a super-giant like Mu Cephei?
February 20th, 2007 at 5:32 am
I’m sure I speak for my antipodean cousins when I say it’s only a lolly if it’s on a stick. Otherwise it’s really just a boiled sweet.
February 20th, 2007 at 7:08 am
Ray Gray: “Or, 93,000,000 miles times X= Sun is invisible
What is the answer to “X†?”
If we take the BA’s figure of 60 light years as accurate (which, assuming magnitude 6 is the dimmest the human eye can make out, matches up with my figures pretty well), 60 light years is about 3.8 million AU. So “X” would be about 3.8 million.
February 20th, 2007 at 2:13 pm
# Alex Whiteside Says:
February 20th, 2007 at 5:32 am
I’m sure I speak for my antipodean cousins when I say it’s only a lolly if it’s on a stick. Otherwise it’s really just a boiled sweet.
——
No, no, no. In Australia, the real centre of the world, a lollie is any sweetie or candy. Minties are a lollies as are M&Ms etc. Over the next few years we can expect to see all of Phil’s teeth fall out.
February 20th, 2007 at 9:48 pm
Heh. I almost expected a crunchy sound at the end of the video (after the disclaimer about the minties).
February 21st, 2007 at 6:21 pm
In the visible wavelength range we see only stars in a distance up to 1 kpc (about 3000 light years)in our galactic disk. In general farther stars are hidden by gas and dust. There are, however, exceptions, small angular windows where we can look considerably farther. E.g. we can see some red giants that are considerably closer to the galactic center than we are. A detailed article on this topic was published in Sky and Telescope, August 1976, p 104ff (“Penetrating Puppis” by Fitzgerald and Moffat). All the best Jurgen
February 22nd, 2007 at 1:52 am
Erlando, I’m glad you liked it!
One of the things I love about astronomy is just how humbling it is.
February 22nd, 2007 at 5:33 am
Luis Armendariz Says:
Heh. I almost expected a crunchy sound at the end of the video (after the disclaimer about the minties).
Minties aren’t crunchy
February 22nd, 2007 at 3:03 pm
NUTS.
Eta Carina is 7500 light years away, and is visible to the naked eye.
Looks like I need to issue my first Q and BA correction. :%
March 4th, 2007 at 4:45 pm
Hi “Bad Astronomer” – I suppose that you refer to my previous posting. The limit of visibility of about 3000 light years is an average value. Very luminous objects (like Eta Carinae) can be seen over larger distances. Moreover, in the article I mentioned several “winows” are described where a consioerably farther view occurs. If you think of the average visibllity limit as of a sphere with a radius of 3000 light years surrounding us, these windows appear like fingers stretching far out of the sphere. I do not know whether Eta Carinase lies within such a window. As the galactic disk is only about 300 light years thick, the view is not limited by interstellar absorption e.g. perpendicular to the plane of the galactic disk. All the best Jurgen