Stellar Fingerprints

When you look at the night sky from your backyard, do you sometimes think that there is no order to all of those stars out there? If the star isn’t part of a well known constellation, is it nothing more than a point of light in a sea of other points of light? Nothing that distinguishes it from any other star?

Well, this just isn’t so. In fact, stars have characteristics such as temperature, luminosity (brightness), mass, galactic location, distance to the earth, and even age — all combined forming a stellar fingerprint that uniquely identifies a specific star.

You probably already know this, but did you ever stop to wonder how we came to know these unique characteristics of a star? After all, we can’t run up and stick a thermometer in a star, or run a tape measure from the star to Earth. So, how do we find get information about stars?

Finding the distance to a star

Well, this one had me the most curious, so this is the one I’ll take first. How do we measure the distance to a specific star? If the stars are nearby, we use stellar parallax

When you move towards objects that are near you, they seem to move in relation to the objects that are located much futher than you. You might notice this when you look at signs by the side of the road in comparison to the background detail when you’re traveling in a car. You can also notice this effect when you hold a pencil in front of you and view it through one opened eye and then another (see diagram).

This same effect seems to happen to stars that are close to the Earth. If you measure the angle to a star from a fixed point on the Earth, and then measure it again from the same point when the Earth is at the opposite position in its orbit around the sun (in 6 months time), you’ll find that the two measurements form a triangle where they intersect (see U of Oregon Diagram). If you half the triangle and then take the angle of one half, you’ll get a value in arcseconds (an arcsecond is 1/360 of a degree). You can then find the distance to the star using stellar parallex:

d = 1/p

The distance to the star (in parsecs, roughly equal to 3.26 light years) is equal to the inverse of the parallex angle of the star.

A light year is the distance light travels within a year — roughly 300,000 km/s

Using this approach we’ve been able to find the distances to several stars such as Proxima Centauri at 0.772 parallax (4.22 light years); Sirius B at 0.379 parallax (8.61 light years); and Epsilon Indi at 0.276 parallax (11.82 light years).

Of course, this approach works only for stars that are relatively close to the solar system, but once you have this information, you can use the distance in other calculations — such as to find the luminosity of a star.

Finding Luminosity

A star’s brightness is a measure of its luminosity.

Luminosity is the amount of light energy emitted by the star within a second, measured in watts (joules per second).

You might think that luminosity is directly related to the distance of the object from the Earth. Well, it is, but there are other factors involved such as the mass of the star and its temperature. If star A is further from the Earth than star B, but star A is much, much brighter, it can appear more bright to us than the closer star.

Still, the distance to the star can tell us its luminosity, with a simple formula:

L = 4pid2b
In this, the Luminosity is equal to the distance squared, multiplied by the brightness, and then multiplied by 4 times pi (pi approx equal to 3.1415926...). The brightness is the apparent brightness as its measured here on Earth (or wherever the viewpoint is), through techniques such as photometry. The brightness of a star is usually described by comparing it to Sirius A, the brightest star we see from Earth (and with a brightness of 1.0).

A simplified approach to finding luminosity is to plug the Sun's brightness, distance, and luminosity into the formula and then take the ratio of the two equations. By doing this, the value of 4pi falls out of the formula:

L/Lsun = (d/dsun)2 b / bsun

Luminosity can now be found by direct comparison between the star and the Sun.

For instance, if a star has a brightness of 5.2 x 10-12 compared to the sun, and it’s distance from earth is 5.2 x 106 that of the Sun to the Earth, you would use the following to find the luminosity:

Lstar/Lsun = (5.2 x 106)2 5.2 x 10-12 = 140

The star (Regulus) has 140 times the luminosity of the Sun, but appears dimmer because of its distance. You could use this same approach with any two stars — find the ratio of the stars and then solve for the unknown value:

L1/L2 = (d1/d2)2 b1/b2

With this, if you find out that star 1 is 3 times the distance of star 2 and appears twice as bright, you can figure the luminosity without having to use a calculator: star 1 has 18 times the luminosity as star 2.

Another characteristic you can find out about a star from the light it emits is its temperature, found next.

Finding a star’s temperature

Quiz time: which is hotter, a blue star or a red star?

The answer might surprise you — the blue star is hotter. The blue color is because most of the star’s radiation is in shorter wavelengths, hence in the blue to ultraviolet range. A cooler star has a longer wavelength, in the red to infrared range.

Wien’s Law states that as a star’s temperature increases, it’s color shifts to the blue.

You can find the temperature of a star by finding the wavelength of its maximum intensity, and using this value in the Wien’s Law equation:

wavelengthmax = .0029 / T

In the equation just shown, the maximum wavelength emission is equal to a constant value (.0029) divided by the temperature. The maximum wavelength emission can be found using instruments on Earth, so this value is used to find the star’s temperature:

T = .0029 / wavelength max

If a star has a maximum wavelength of 500 nm (5 x 10-7 m), its temperature would then be about 5800 degrees kelvin:

T = 0.0029 / 5 x 10-7

This is the temperature of our own Sun. Its color is due to the fact that the maximum wavelength emission is at 500nm, putting it within the yellow color range in the visible light spectrum.

You can find the maximum wavelength emission of any star using photometry, regardless of its distance from the Earth.

Of course, once you have a star’s temperature, and its luminosity, you can then find its radius.

Finding a star’s radius

Okay, let’s recap what we’ve been able to find out about distant stars.

We’ve been able to find their distance (if close enough to use stellar parallax), as well as their luminosity (regardless of distance). We can also find a star’s maximum wavelength emission, and we’ve used this to find the star’s color as well as temperature. One thing we haven’t found, yet, is a star’s size. We have found, though, the values necessary to find the radius of the star: its luminosity and it’s temperature.

A star’s luminosity is equal to its radius, squared, multiplied by its temperature to an exponent of 4:

L = 4piR2(const)T4

The (const) value in the equation is the Stefan-Boltzmann constant, a value of 5.67 x 10-8 W m-2 K-4. (Find other constants.)

You don’t have to remember this rather computationally instensive formula if you look at it as a measure of the ratio between the star and the Sun:

L/Lsun = (R / Rsun)2 (T / Tsun)4

Re-arranging this to search for the radius, you have:

R/Rsun = (Tsun / T)2 SQRT(L / Lsun)

For instance, the star Rigel has a temperature 3 times that of the Sun, and a luminosity 64,000 times that of the Sun (one very bright star). It’s radius in comparison to the Sun’s is:

RRigel/Rsun = (1/3)2SQRT(64,000) = 27.5

Rigel has a radius about 28 times that of our Sun. As the Sun’s radius is 6.96 x 105 km, Rigel’s radius would be about 1.9 x 107 km.

An so on…

There are other things we can find out about stars, but this should give you an idea of what we know, and what we can find out about a specific star.

And we didn’t even have to leave our backyards to find it.

New York, New York

t isn’t Fall without trees changing color, birds flying south for the Winter, and being in New York to speak at the Internet World conference — this time as part of the Webmaster Forum.

However, this time, I stayed in New York for a few days. What an adventure.

New York Cabbies

The cab that took me from Penn Station to my hotel was driven by a gentleman from Haiti who happened to have strong religious beliefs. I know he was religious because he kept playing religious tapes, and would slam on the brakes occasionally in order to jot something down in a notebook he kept by his seat. I knew he was Haitian as he would alternate this behavior with Haitian utterances under his breath as he literally tore through that town, determined to get me to my hotel at all due speed.

I didn’t know one could drive between cars in car lanes in New York. I also didn’t know that one could drive 60MPH down Park Avenue in the middle of the day. I do now. I also received a lesson in the finer points of car horn blasting in New York.

There’s the light tatoo on the horn that says “Yo!”. There’s the more emphatic tatooing that seems to say “Yo! Stupid!”.

There’s the single tap that just lets folks know you’re in the vicinity and to watch out. Compare this with the heavy hand on the horn that will get even the most diehard New Yorker’s attention. If the horn blower is a cab driver, people seem to understand that the cabby is just letting someone know that they are invading the driver’s personal territory, whatever that may be.

I also know that pedestrians in New York don’t walk in front of the cabs without looking at the driver’s face, first. How does this driver define territory…

Cab rides are a way to experience New York, but I can’t experience a new town or city from a car — I just don’t like cars. So, I decided to walk to Central Park. On foot. No cabs.

Walking to Central Park

I started my walk on Madison Avenue — established home of advertising agencies everywhere.

Madison Avenue doesn’t have the crowds other streets do in New York, thought there are a large number of gray and black suited people, all with cellphones glued to their ears (call them New York earrings).

The buildings along the way reminded me of some of the canyons I used to explore in Arizona, except those canyons were created by water flows over a millenium of time. New York canyons are built on man’s desire to one up nature. I did notice, though, when I crossed over to Fifth Avenue that the human tide is remarkably similar to a moving river. Woe to you going against that tide of affluent and determined shoppers.

(I particularly treasure a moment when two older, well dressed women walking behind me suddenly stopped in the middle of the sidewalk and murmured “Armani” in one breath. I consider this to be a quintessential New York moment.)

The Park

Central Park is a surpise after all the opulence of the surrounding stores and the shadows cast by the towering buildings elsewhere in downtown New York.

Part of the Park was closed off for renovation, but I walked every last bit of those sections that were open. And it was a long walk.

First, let me state categorically that I cannot BELIEVE that anyone would jog in the Park after dark. The place is full of nooks and crannies, dark corners, and bushes. Charming by day, sinister by night. A horse carriage ride, yes — but not a lonely stroll through the footpaths. I’d rather play tag with a grizzley. It would be safer.

Central Park is pretty, but the trees look a little tired, and more than a bit dusty. However, the bushes and lawns were very pretty, as were the little specialized areas such as the Dairy farm.

I found an old fashioned carrousel and thought about taking a ride, but dignity intruded — dammit.

My favorite sections of the Park were rocky outcroppings with bits of mica scattered about, sparkling in the noon day sun. Something like the windows at Tiffany’s and Cartiers I passed on the way, only I could touch the rocks at Central Park and not get arrested.

I actually saw a black squirrel; I’ve not seen one of that coloration before. I don’t have my books to check to see if this is a natural variation, or a protective adaption based on New York city smog. (I know, meow, meow — but Boston is a whole lot greener.)

I walked through some bushes at one point and found a group of people silently standing around a mosaic embedded in the cement. All the mosaic had on it was the single word “imagine” — I was in Strawberry Fields, the John Lennon memorial.

One word, and I stopped dead in my tracks. One moment, with a lifetime of memories, flooding in, all because of that one word.

Back from the Park

I was getting tired at this point, so back to the hotel.

Towards the end of my walk, I stood out in from of St. Patrick’s Cathedral, an incredible edifice of which New Yorkers take considerable pride. If you’ve been to New York, you know what it’s like to come upon the Cathedral after blocks and blocks of modern glass and steel.

I have to admit that when I first looked at St. Patrick’s, I thought of how much further we would be as a people if only we expended as much energy and resources on education as we did and still do on religion.

We could have cured cancer by now, eliminated all smog and pollution, perhaps be walking on some distant planet around some distant sun.

Then I walked into St. Patrick’s. I literally stopped in the middle of the Vestibule, overwhelmed by the absolute rightness of the interior of the church. The vaulted ceilings, the stained glass windows, the slight smoky air from thousands of votive candles lit by the faithful.

It then came to me that without faith — or perhaps human spirit — we wouldn’t even try to cure cancer, or walk on the moon, much less planets surrounding distant stars. And we wouldn’t have beauty such as that.

Maybe we didn’t do so bad with our time and our resources in the past, after all.

New York, New York

My last stop on my walk was Rockerfeller Center, located a couple of blocks from the hotel. As I approached the Center, I could hear the strains of the Sinatra song, “New York, New York” filling the air. I kid you not — there had just been an ice show at the center, which finished by playing New York’s anthem song.

I couldn’t end my walking tour of New York on a better note than that.

O’Reilly P2P Presentation Proposal

Title: Smoke: An Infrastructure supporting Distributed Peer Services

Length: 60 minutes

Focus of Talk: Technical/Tutorial

Subject Matter: Infrastructure/Distributed Computation


The sale of large scale control systems — such as those used with mass transit systems or to control multi-national pipelines — often requires a marketing and engineering effort that demands the input of several different people, many of whom live in different countries and speak different languages. To assist in this effort, a project is underway to create an automatic configuration tool that allows these team members to work in a collaborative manner, regardless of each member’s locale.

Because of a lack of infrastructure for applications of this nature, the developers designed one that is based entirely within P2P-based concepts and technologies.

This infrastructure, named Smoke, is unique in that it’s based on the concept of shared distributed peer services — services that are lightweight, discrete, and transient — existing within a framework that is both open-application and cross-platform compatible.

At the presentation, the speaker will provide an overview of Smoke, as well as demonstrate a working prototype of the automatic configuration tool. To display Smoke’s open-application and cross-platform support, three variations of the configuration tool prototype will be demonstrated: one with an interface created with Mozilla’s XUL and hosted on MacOS; one accessed through Enterprise Java Beans (EJB) hosted through an Apache WebServer and WebLogic on Unix; and one accessed through Groove, another P2P infrastructure product, hosted in Windows 2000.

Smoke is an open source infrastructure, which means it can be used by any developer interested in working within a P2P distributed peer services environment.


Shelley Powers will present an open source P2P infrastructure that supports the concept of distributed peer services: services that are lightweight, discrete, and transient. A prototype large scale control system configuration tool is used to demonstrate the infrastructure. Three different variations of the prototype will be shown, to demonstrate both the open-application and cross-platform capability of the infrastructure and the tool.

Speaker: Shelley Powers

Speaker Biography:

Shelley Powers is a consultant/author with her own company, the Burning Bird Corporation, currently located in Boston, Massachusetts.

In the last several years, Shelley has worked on several distributed and Web-based applications on a variety of platforms. In addition, she has also authored or co-authored books on Dynamic HTML, JavaScript, Java, CGI, Perl, P2P, and other technologies, as well as writing for several publications including Webtechniques, MSDN Journal, Netscapeworld, and O’Reilly Network. She’s the author of O’Reilly’s Developing ASP Components, second edition. Shelley can be reached at

Australian Censorship bill could impact on P2P

Originally published at O’Reilly

Australia’s been in the news before about Net censorship legislation, but the South Australian Parliament may have gone a little extreme even for this Net-conservative country.

A bill introduced in November would make it illegal for content providers to post material that is considered “objectionable viewing material” for children. What’s objectionable viewing material? Anything that the police — the police, mind you — would consider as falling within the R, NC, or X ratings categories of the film industry. Ostensibly this would cover material such as child pornography or content advocating breaking the law. However, the bill is general enough that it could also cover material on topics such as abortion, suicide, drug use, sexual behavior and other sensitive topics that could be termed “adult topics” and therefore R-rated.

Even more alarmingly, under this bill posting this material is illegal even if access to the material is restricted or password-protected. Compounding the problem, content providers would have no way of knowing whether their material would fall under one of the prohibited classifications before posting it; if the material is judged by the police to be within the parameters of this bill, you’d be charged. No warning and no second chance. And the fines aren’t cheap: as much as 10,000 (Australian) dollars per offense.

According to an alert issued by Electronic Frontiers Australia, this bill would actually make material that’s legal offline, illegal once posted online.

The impact of this bill on Web-based businesses is obvious — the level of censorship implied would give even the most conservative businesses pause when it comes to posting content on their Australian-based Web sites. What may not be so noticable, though, is the impact of this bill on peer-to-peer applications and services. You see, the wording of the bill doesn’t focus on Web-based content; it concerns content distributed via the Internet.

Consider the following scenario: You’re a subscriber to a file-sharing P2P service such as Napster. You make a request for material that could be considered “objectionable” because of the language used — for instance one of the more explicit songs from Alanis Morissette’s album “Jagged Little Pill,” or practically anything from Guns N’ Roses or Eminem. Once you’ve downloaded an “objectionable” song, it’s now on your machine for your personal use. However, in this process, you’ve also “posted” this content for access by other clients through the Internet: P2P is based on the fact that any node within the network can be both a client and server. According to this bill, you would be in violation of the law.

If you’re a subscriber to a decentralized service such as Freenet or Gnutella, the potential problems with this type of bill are even more extreme. With these types of P2P networks, if a file request is made from node A to node B, and then from node B to node C, that file is returned to node B as the intermediary first, and finally to node A. Now, not only is the peer located at C in violation of the law, so are A, who originally requested the file, and B, who did nothing more than subscribe to the conditions of the P2P service that states files may be stored on the client’s machine as a method of disseminating popular files throughout the network.

By its very nature, Freenet hides the identity of nodes supplying or requesting files, making it difficult to ascertain who was the originator of the material or the request. Because of this, it becomes difficult to ascertain who is legally responsible for “posting” the file if it is deemed to fall within the parameters of this censhorship bill. So, what could happen is that the intermediary node containing the file is the one charged with violating the law, rather than the originator, regardless of the technical and legal semantics that form the basis of anonymity within a Freenet network.

At the very least, applying this censorship law to the Freenet or Gnutella network would become a legal nightmare to the South Australian court system. All it would take to demonstrate the unfeasibility of the law is to introduce one highly popular but objectionable file to Freenet, potentially turning all or most South Australian Freenet users into criminals. This issue goes beyond considerations of copyright law.

According to the UK-based Register the South Australian’s politicians must have gone “barking mad” — in other words, the bill’s sponsors may want to reconsider the bill on its own merits.

Read the pertinent sections of the censorship bill at Electronic Frontiers and then join discussions at Slashdot and South Australia’s Talking Point

Browser, Browser Not

Originally published at O’Reilly

Recently, O’Reilly published a set of articles (Netscape Navigator 6.0 to Fail Standards ComplianceAn Update, and Netscape 6.0 Released), written by the popular author David Flanagan, about the release of Netscape 6.0, Netscape’s newest entry in the browser marketplace.

David presented several valid concerns about bugs still present in the release of Netscape 6.0. And it is true, Netscape 6.0 did release with several unfixed bugs, many of which will have an impact on support for W3C specifications.

Our reaction to the release, however, was somewhat different. Along with other application developers, we’ve been waiting for the public release of an application that uses Mozilla’s XPToolkit, a set of software components from which Netscape 6.0 and the upcoming Mozilla 1.0 were built. Now that Netscape 6.0, which uses this framework, has been publicly released, we’re delighted: testing of XPToolkit may begin in earnest.

While many are focused on the release of Netscape 6.0, some of us aren’t. We’re more interested in the application environment created by the Mozilla team to support the implementation of browsers in general. To us, this framework is more important than the release of a new browser will ever be.

The reason for this is the changing face of the Internet, itself.

The Changing Face of Internet Applications

Current Internet applications rely on a centrally located Web server to distribute HTML over HTTP to clients. Each client, or Web browser, renders the source and displays a human-readable page.

This architecture has become so popular that you can’t pick up a magazine or a newspaper without hearing about Web servers or the new business models based on them. Although this architecture is based around universally located resources, most application-level resources are centralized and many other resources are hard to find. Some Web sites help you find other Web sites or “resources.” Others go so far as to offer completely centralized applications, as Application Services Providers (ASPs).

New technologies will soon force us to rethink the way we use the Internet. Distributed systems, mobile agents, and peer-to-peer (P2P) applications may completely undermine the need for browser-based Internet access.

P2P applications are already stepping around the browser. The next step will be around the Web server.

Consider this: a P2P application that locates and downloads a new function. The simplest example here may be provided by a P2P execution framework that uses XML-based remote procedure calls between peers to marshal XML-encoded functions. Instead of hitting Web pages, each peer locates and accesses both data and functions among a network of peers. No Web servers.

This scenario is not going to be best served by the traditional browser. Why?

The Limitations of Browsers

The things that made the Web browser a success in the beginning are the things that make it ineffective for new application models.

The browser was built to render files stored on Internet sites so we didn’t have to muck about with FTP. As soon as content became more visible, people started publishing yet more content, so browsers rendered HTML, then XML, formatted with CSS or XSLT. However, the browser itself has a very limited interface, even with new advances in W3C specifications. Sophisticated browser pages mean using either complicated object models–leading to cross-platform and cross-browser idiosyncrasies that are usually the result of standards initiatives–or using page-embedded applications, such as Java applets and plug-ins.

Even when the browser follows standard specifications, working within a browser page to create a sophisticated interface isn’t a simple or uncomplicated task.

In addition to the browser becoming increasingly complex as the nature of content becomes so, use of it implies that applications ought to be served from one location, and in one manner. To do something such as make a remote procedure call, you would need to use a digitally signed Java applet or some other browser-specific and limited technique. This is something that won’t bother newer P2P applications.

Finally, browsers were designed to be safe, and operate in a protective sandbox. Web-based applications served via a browser have difficulty getting at the user’s machine. Though safe, this restriction also prevents behaviors that would have the application modify its user interface. And this dynamism is going to be necessary in an environment where new services require new application interfaces that can be downloaded as data.

An Internet Application Framework?

Mozilla made a tough decision a few years ago–to scrap the Netscape 4.x architecture in favor of one built from the ground up. In the process, this open source team created an application environment based on reusable and interchangeable components.

With this application environment in place, the team then proceeded to build a sophisticated browser. They threw in Internet Chat, a Web page composer, and other complex things, all of which were released recently as Netscape 6.0. Often forgotten is that a powerful application environment came with it. This environment is now usable by developers of other Internet applications.

What types of applications? Well, ActiveState, the company that provides popular implementations of Perl and Python for various operating systems, used Mozilla to create itsKomodo product, a visual IDE for working with Python and Perl code. The user interface provides, among other things, colored syntax, syntax checking, and source-level debugging.

So, we have a browser and an application that can be used to create and test Perl and Python applications, all built from the same application architecture.

This is exciting stuff! Much has been written about reusable code and component-based design, and now we have an open source application environment we can all use to build our own applications.

Even more exciting is the extensible user-interface language from Mozilla called XUL (pronounced “zool”). It’s based on XML, which means you can use XML to create a user interface. Combine this with the ability to make remote procedure calls, and you have a perfect place from which to commence building a bunch of P2P applications, based on the scenario mentioned above.

Now, instead of opening a browser, you can open an application built on the same framework as your browser, but with a sophisticated interface of dropdown menus and tabbed pages–all created using XML. You can access remote procedure calls at the touch of a button and when you’re ready to access a new service, click another button, and in a couple of minutes restart your application. New entries will be added to new or existing menus providing access to the new service. All this is accomplished without Java bytecode, a new plug-in, or a DLL.

You’ve just downloaded XML.

When you explore the possibilities of the XPToolkit from Mozilla maybe you’ll agree that Netscape 6.0 is more than just a standards-based, better-than-Navigator-4.x-browser. It’s the start of a new new way of doing things on the Internet.