A Spiral Galaxy with Attitude

By Doug on September 30, 2006 at 8:09 pm | In Blog Posts | No Comments

No doubt you have seen beautiful images of spiral galaxies many times. Those systems with very pronounced arms tend to be imaged repeatedly. In 1925, Hubble established that they were “island universes” - stars and gas grouped together in space at great distances from our system. He did this by recognizing Cepheid variables in M31, and soon thereafter in other Local Group galaxies.

However, there was a question that persisted many years after that revelation - do spiral galaxies rotate with the ends of their arms “leading” or “trailing”? The answer turns out to be “trailing”. But the evidence for that fact was a long time coming.

“Why?”, you may well ask. “Couldn’t they just use a spectrograph and measure the Doppler shift?”. Yes, measuring the Doppler shift is possible and it does tell you whether or not part of the image is heading towards you or away from you. However, what is generally difficult to determine is which side of the galaxy is closest to you!

Find a picture of M83 - a face-on spiral, and M104 (”The Sombrero”) which is close to edge-on. First, look at M83. You’ll agree it is a beautiful thing. Look at it carefully - there is no clue as to which side is closest. Now look at M104. It is abundantly obvious which side is closest because of the obscuring dust lane. Unfortunately, its disk is inclined so close to edge-on that the direction of its spiral structure is undetermined! That, in a nutshell, was the observational situation for a long time. You could either see the pattern, or know which side was closest, but not both at the same time.

Hubble finally found a galaxy where you could have your cake and eat it, too. In 1943, he wrote a paper entitled “The Direction of Rotation in Spiral Nebulae” in the Astrophysical Journal. The galaxy which finally yielded this secret was NGC 4216 - a largei, well-inclined spiral in the Virgo Cluster that is easily seen in amateur telescopes. It is inclined just enough for a prominent dust lane to reveal the near-side and little enough for the spiral direction to be clearly discerned.

It can be located on any clear April evening. Even though it does not have a Messier number or a fancy name, it still played an important role in allowing us to understand how real galaxies behave.

[I wrote this piece many years ago for the newsletter of the Hamilton Amateur Astronomers. It seemed like the sort of thing which might interest SG readers!]

Lights Out

By Michael on September 27, 2006 at 10:07 pm | In Blog Posts | No Comments

This is cool: Lights out in Iceland for view of night sky.

Authorities in the capital Reykjavik will turn off street lights on Thursday evening and people are also being encouraged to sit in their houses in the dark, writer Andri Snaer Magnason said on Wednesday.

Now if we could just do that every night!

Stars and Pressure

By Michael on September 26, 2006 at 12:47 am | In Astrophysics, Blog Posts | No Comments

In my last post I talked about the balance of forces that make stars, like the Sun, stable. I said we could learn things about stars by understanding this balance. Here is an example.

We ended up with this equation:

GMp/r^2=dP/dr

This is not as complex as it looks. The big G is just a number based on the units we are using. The M is the mass of the star. The funny looking p is the greek letter roh and it is the density of the star. r is the radius and the big P is the pressure. We can make this more simple if we assume the pressure is zero at the surface of the star. We’ll also change the density back to mass divided by volume so we can combine some terms.

P=(3/4)(GM^2/R^4)

The pressure P at the center of the star is proportional to the square of the mass and inversely proportional to the 4th power of the radius.

So if two stars are the same size and one is twice as massive as the other (and obviously much more dense as a result), the pressure in the center increases by a factor of 4. If two stars are the same mass but one is half as big as the other, the pressure at the center will be 16 times more.

If you Google the mass and radius of the sun and the value of the constant G you can calculate the pressure of the sun with the equation above. Try it!

A blog about getting there, and a blog about being there

By Aaron on September 23, 2006 at 4:45 pm | In Blog Posts | No Comments

Kwajalein
One of the cool things about the Internet is that it breaks down barriers. I’m a big believer in transparency. I think transparency can make almost any problem better, but more than that, it is even more influential in preventing problems in the first place.

A good illustration of this is the Kwajalein Atoll and Rockets blog. It’s a blog run by a user called Kimbal who is somehow associated with work at the Kwajalein Atoll. For those who don’t know, Kwajalein is a bunch of tiny rocks sticking out of the south pacific. The US department of defense has lots of military installations there, most associated with space exploration and signal intelligence. Private companies also have installations there. Among those is SpaceX, a new company founded by a co-founder of PayPal. Their goal is to create incredibly cheap space launch vehicles.

In February, Kimbal, who seems to be an employee of the company, started the blog to document the maiden test launch of one of their rockets scheduled for late March. Reading the nearly daily entries in the blog is mesmorizing! Kimbal discusses aspects of both the launch and of life on the tiny island. Each day you see the challenges and solutions they come up with. Over time you get a feeling of what it must be like preparing for such an important test. He gives detail examples of things that go wrong and those that go right. Then, on the day of the launch, he takes you through it minute by minute.

This is where it went from enlightening to down right entertaining. Not only did he blog the launch, but they put a web cam inside of the rocket. And it was a good quality cam to boot. So the rocket did launch. But I won’t spoil the surprise, read the blog to find an ending that you couldn’t have scripted with the best Hollywood writers.As a recent bonus, they’ve been selected as one of the contractors to possibly build the new crew exploration vehicle for NASA and they’ve posted concept images and info in the blog.

Side notes:
Here are a couple of links from the ASP meeting which I left out of the last post, but found while subsequently going through my notes:

The University of North Dakota is offering an online MS in Space Studies degree.

The Informal Science Education Research Group in Astronomy is asking the public to take a survey about the Pluto debate. They seem like an interesting group of students at Columbia University studying science education (mike type of crowd!). But the survey is more like a vote and there is no explanation as to why they are doing this and what it is for.

Report #2 from ASP Meeting

By Aaron on September 18, 2006 at 11:26 pm | In Blog Posts | No Comments

The talks I attended Sunday were of an introductory nature so I didn’t really learn much. But they were good for that level and for the limited time the speakers were allotted. A positive exception was Dr. Ed Prather’s talk. For 30 minutes he challenged educators to not just throw stuff at the audience but to also assess and evaluate the program to make sure real learning is occuring. He suggested more contextual learning and student centered discourse in the classroom. As someone new to the education research field, I’m very interested in hearing different points of view and where the perceved weaknesses in the field are. I am seeking permission to play snippets of his talk in an upcoming SG podcast and discuss it with our own Dr. Doug Welch, who is an E/PO professional as well. So stay tuned.

The afternoon plenary session was devoted to a producer of the Nova series on PBS. Nova has held a special place in my heart because it was the best (and usually only) place to go for quality, in depth science coverage on television as I grew up. But now there are tons of (self described) science channels, web sites, podcasts, CD-ROMs, etc. And I think Nova must be feeling the heat because their shows are not what they used to be. The talk was an example of that. It was nothing but a long series of commercials for Nova. The speaker (a producer) would read a script for a minute or two and then show a 5 minute clip of a show, including advertisements for the upcoming season which was dominated by high energy “re-enactments” of airplane crashes, explosions, etc. It reminded me much more of a trailor for “Final Destination” than a science show. The speaker could have been talking to an advertising convention and not changed a bit of her presentation. And I wasn’t alone in this sentiment.

The American Museum of Natural History in New York has built a truly amazing planetarium system over the past decade and they showed us more of what is to come. They are focusing on using real data in their presentations, live when possible. For example, when they give a show they will sometimes connect with others around the world, interview them live and show (on the dome) the night sky of the person they are speaking with. One person they may sometimes pipe in live is Reid Stowe, who is sailing around the world for 1000 days without reaching sight of land. He chose 1000 because that is how long it will take astronauts to visit Mars and return.

NASA is considering starting an online Masters of Science degree in Education & Public Outreach (EPO). I think this will be the first MS degree in science EPO in the country (the world)? They plan to hold a trial class in early 2007.

A poster about the Hubble Heritage Project had some really awesome 3D glasses of Hubble Heritage pictures. They are developed by A. Inaka, an amateur in Japan. The quality of these 3D images is fantastic. The colors are rich and the
light (sourced by the ambient light in the room) is strong. I would totally buy these as Christmas presents if he made them for sale. Instead, he makes them for fun and sends them to the Hubble team to use for outreach like this. Amateurs never cease to amazine me!
NASA has some robotic telescopes which they have been using in educational settings for a few years. Now they are granting access to the telescopes to the general public. You choose a target, set the exposure level and submit the request. The image will be ready in about 48 hours.


Sunday ended for me at about 3am after late night “networking” in a local bar that had a “half way to St. Patricks Day” special on pints of Guiness. I had a 8am train ride home and slept from Baltimore to New York. I’ve said it before and I’ll say it again, rail is the best way to travel. It’s a little slower than air travel - but it is relaxing, easy and much more productive. As I write this blog entry the Connecticut countryside is speeding by. In fact, I’ll take a picture. There. To the right is what I’m seeing out of my window right now. The only downside is having to put on headphones to drown out this guy’s snoring:

Overall, while the sessions were not particularly applicable to what I do, the meeting was very useful due to the sheer amount of networking that went on. I met a ton of new people and hopefully planted the seeds for some future collaborations. Now on to the AAS in January, where we can report on some real science discoveries.

Why Stars are Stable

By Michael on September 18, 2006 at 3:35 pm | In Astrophysics, Blog Posts | No Comments

Hey slackers!

So I am taking a class about the structure and evolution of stars. I have been taking classes for 6 years (albeit one class at at a time) just so I would have the math and physics background to take this class. As someone that got into the quantitative side of astronomy via variable stars, I want to understand stars. Lucky you, I’m going to take you along on some of the concepts as they are introduced in this class. Today I am going to talk about hydrostatic equilibrium. It’s a fancy term that explains why stars are stable most of their lives. It goes like this…

We all know that gravity is an attractive force. So if I have a little blob of material in a star, gravity is going to try to pull that blob towards the center of the star. But we just said that stars are generally stable, meaning that the material can’t be free-falling into the star — something is resisting the force of gravity. In physics if things aren’t moving we call them “static”. So if this blob of material in a star or the sun is static, there must be some force opposing gravity. Mathematically we can write this as an equality:

Hydrostatic Equilibrium Equation 1

Here the “g” stands for gravity and the “b” stands for buoyancy. We don’t know the buoyancy force is yet, but we know something is pushing that material outward.

We know how to write the force of gravity:

F_g=-GMm/r^2

Newton gave us this equation. The G is the gravitational constant, the big M is the mass of the sun or star and the small m is the mass of the little blob of material.

Pressure is force per unit area. So if I push my hand on your back, the pressure you feel is the amount of force I am exerting divided by the area of my hand. If I used the same amount of force but with a much smaller area, say the point of a knife, the pressure is much greater and I stab you in the back. Much more force can be applied on your back, say by your seat on an airplane as it takes off, provided the area is greater.

We know that gas has pressure, just like the atmospheric pressure here on the surface of the earth. There is a pretty simple formula for gas pressure:

P=nRT

Ignore the n and and the R for now — the P stands for pressure and the T stands for temperature. So the pressure is proportional to the temperature. The force from pressure is a little different in this case, though, because in order for gas pressure to exert a force it has to be unbalanced. In a star (and on Earth) the pressure is greater the closer you get to the center. So even for a small blob of material, the pressure at the bottom is greater than the pressure at the top. Physicists call this a gradient. So the force from gas pressure in this case is related to the difference in pressure between the top and the bottom of the blob. We are calling the “buoyancy” force above by its true name now, the gas pressure.

F_p=-dP dA

If you are not familiar with calculus, the small “d” in front of the P (for pressure) and A (for area) means a vanishing small change. So the equation above is stating that the gas pressure is equal to a small change in pressure times the tiny little area of our blob of gas.

With me so far? Now the point: we set the two forces to equal each other, since the material is static and not moving.
GMm/r^2=dP dA
One last little bit of algebra, replacing the small “m” on the left with the density and the volume (because density is mass divided by volume so mass is density times volume) lets us cancel some terms and rearranging others we get:

GMp/r^2=dP/dr
So the gravitational force is equal to the ratio of the change in pressure (dP) to the change in radius (dr). The forces balance and the star is stable for millions of years. Were these two forces to become unbalanced it would cause sizable changes to the star in a matter of hours!

This is all a little deep, perhaps, but congrats for wading through it. This is an extremely important concept in stellar structure. Next time I’ll talk about some cool calculations you can do with this to learn things about the Sun and stars.

More info and illustrations of hydrostatic equilibrium are here: http://jersey.uoregon.edu/~imamura/208/jan27/mech.html

Report from the Annual Meeting of the Astronomical Society of the Pacific

By Aaron on September 16, 2006 at 9:18 pm | In Blog Posts | No Comments

Greetings from Baltimore. The theme of this meeting is education & public outreach, which is becoming somewhat of a mantra for the ASP. I haven’t seen any hard score science sessions yet, although the ASP publishes a major scientific astro journal.

The first talk I saw this morning was by Pamela and Phil Plait. Technically, I was a coauthor on that talk too. But I didn’t really contribute anything to it. Therein lies an illustration of an astronomical law. It is easy to get your name on an astronomical paper these days. Usually (but certainly not always), the last name(s) on a paper listing are there for beaurocratic and/or technical reasons. For example, they work in the same department. Or they wrote a piece of the grant that funded the work by the researchers. Or they are dating the first author’s sister.Well, maybe the last one doesn’t happen so often. (Do astronomy geeks even date?!?) But the point is that the first few authors do 90% of the work 90% of the time. Call it a 90-90 rule.

Their talk was about managing message forums and listserves. Such forums are becoming more and more frequent as astro organizations realize that they truly can trust the communities they serve.

It was announced that Google is working with the Space Telescope Science Institute (they who bring you HST, among others) to create a fancy version of Google Universe. Right now it uses SDSS data. One of the cool features it has is a press release overlay. So when an HST press release is issued, a spot appears on the point in the sky where the object of the press release is located. So you can just surf the sky and click on objects to get nice HST imagery and metadata. In a visualization session they demo’d it and it was impressive, as one would expect. The big worries are bandwidth. Google said to expect over a million requests per hour, but no one really know what to expect. And how to you prepare for an infinite range? This technology will play a key role in the long term development of data mining and distribution online. Right now the pros use sites such as ALADIN to overlay datasets. But its getting long in the tooth and smoother, fancier technlogies are needed to prepare for the upcoming firehouse of data that will come from the new telescopes now under construction.

I gave a talk in the afternoon about new media, and how to integrate it into outreach strategies. The key message is what is driving the new Slackerpedia Galactica projects. Basically, use the right tool for the job. Don’t try to put a web page into a podcast or a podcast into a web page. Use video, wikis, networking sites such as MySpace, etc. Find the tool that fits your message and use it. Don’t try to fit square pegs into round holes and be all things to all people.

That’s about it for today. Compared to AAS meetings, these are much more subdued. People tend to know each other and the pace is slower. The bar in the evenings was deserted! That seemed eery and unnatural to me. Tomorrow I’ll be attending more talks (since I’m involved in less of them) so hopefully will have more to report.

SG #1.0

By Aaron on September 15, 2006 at 11:02 pm | In Audio Podcasts | No Comments

The first episode of the new show is in the can and on the feed, with a skit involving Uranus and its transiting moons. We put show notes here and you can discuss here.

The End of A Planet & A Podcast

By Slacker on September 15, 2006 at 1:21 am | In Audio Podcasts | No Comments

In this show we discussed our personal views about Pluto, then dropped a bomb on the audience. Slacker Astronomy, as an audio podcast, is over.

However, two new podcasts will emerge. Pamela will be co-hosting AstronomyCast with Fraser Cain of the Universe Today web site and podcast. AstronomyCast will take a fact based journey through the cosmos as explores different topics in-depth each week.

Also, Travis, Aaron, and Rebecca will be joined by two new people to create Slackerpedia Galactica, a new eclectic podcast and web site about astronomy.
We thank you all for your support over the last year and a half. It’s been a fantastic run and you’ve given us some memories that we’ll always cherish. We hope that you enjoy the new shows. Think of it this way, you now have twice the astronomy for the same price - free!:)
The first episodes of both shows are online now and appearing in the SA feed. Check your podcast client now to listen.
In the future, SG episodes will be posted to the same feed as Slacker Astronomy. So you do not need to do anything to your podcast client. However, be sure to subscribe to Pamela’s new show via this feed.

Welcome to Slackerpedia Galactica

By Aaron on September 15, 2006 at 1:06 am | In Blog Posts | No Comments

Here is the straight dope:

The Slacker Astronomy audio podcast published its last episode today. Pamela is now co-hosting AstronomyCast with the excellent Fraser Cain. You’ve heard Fraser on our chit chat shows a few times and we regularly use news items from his web site, UniverseToday.com. Pamela will hopefully join us for future Slackerpedia Galactica episodes when her schedule fits.

So what is Slackerpedia Galactica? That is the name of the new audio podcast that we are publishing on the SA feed and web site. Travis and Aaron have been joined by Dr. Doug Welch, Michael Koppelman and Rebekah Turner for this new show. It will be a 1-2 hour chit-chat style show, with some Slacker Astronomy style scripted segments in it. It will be published monthly. But in between the shows each member of the team will record their own shows that will show up on the feed and their topics and formats will be all over the map. The only requirement is 1. they be fun and 2. they be smart. In other words, follow the SA formula. We also have plans to expand into more video podcasting (yes, more Lite Brite tutorials!).

Slackerpedia Galactica is also a wiki - A place for anyone to post astronomy articles written with a sense of humor and silliness, yet still remaining accurate. This will become our crown jewel.

Doug, Michael Aaron and Travis are also going to contribute to a collaborative astronomy blog we will keep on this site.

We have new forums, launched about a month ago. Our goal with the forums is to build a community. So when the forums get to large, we may freeze new memberships. So sign up while you can, even if you just want to lurk.

Don Cook, aka Dr. Deranged, is going to contribute a weeklyish webcomic called Stellar Worlds. I know he has big plans for the stories told in the comic, so check it out.

Thanks for checking us out and sticking around. We hope you enjoy the new site and endevour.

Clear skies and clear bandwidth!

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