History’s Greatest Star Map

Next time you’re out under a clear, dark sky at night, look up and pick out a star at random. Chances are, nobody knew until 15 years ago how far away that star is. Now, thanks to the European Space Agency’s Hipparcos mission, we know.

Your randomly chosen star is probably somewhere between 100 and 1000 light-years away, although there’s about a 15% chance that it’s closer, and about a 10% chance that it’s farther. If your star is one of that nearest 15%, then its distance was probably known, to an accuracy of 50% or better, before Hipparcos. Otherwise, astronomers could have given you no better than a rough estimate of your star’s distance.

Direct measurements of star distances come from the method of triangulation, or parallax: Look at the star from two different directions, and measure its angular shift as you switch viewing locations. It’s the same principle as two-eyed vision, except that in the case of stars, the two viewing locations are on opposite sides of earth’s orbit around the sun—300 million kilometers apart.

Despite this enormous baseline, the angular shifts are miniscule, even for the nearest stars. And for stars beyond 100 light-years, the angles are too small to measure with any accuracy through earth’s blurry atmosphere. So in 1989 the ESA launched the Hipparcos satellite, carrying a special-purpose telescope dedicated to making accurate measurements of the positions of 100,000 stars. By repeating the measurements over a three-year period, the instrument determined not only the parallax shifts but also the steady motions of the stars as they gradually drift across our galaxy. The catalog of results, published in 1997, gives accurate distances and motions for all but a handful of the naked-eye stars, and many, many more.

You can now read about the Hipparcos mission in a new book by Michael Perryman: The Making of History’s Greatest Star Map. Perryman was Coordinating Scientist for the Hipparcos mission, and he does a masterful job at conveying what an immense undertaking it was. Hundreds of scientists spent many years of their careers on Hipparcos, while some of Europe’s most advanced industries fabricated the satellite and its unique optical system. The story also includes high drama, thanks to the failure of the booster rocket that was to put the satellite into its final orbit. That the scientists were able to recover from this disaster and still surpass all the mission’s goals was nothing short of miraculous.

Unfortunately, Perryman’s book has several shortcomings. He tries to do too much, telling not only the story of the Hipparcos mission but also the whole history of astronomy since ancient times—in fewer than 300 pages. Indeed, the main intent of this book is apparently to establish the place of Hipparcos in history, and to properly credit several dozen of the principal scientists for their respective roles. Educating the reader is secondary, and although the book tries to be accessible to non-astronomers (and to wow them with vague superlatives), I fear that most would be overwhelmed by the enormous number of technical details so superficially explained. I learned quite a bit from the book, but I’m already a professional physicist who teaches introductory astronomy. For my own part, I was disappointed that the book didn’t adequately explain how the Hipparcos optical system worked, or even point to a reference where I could learn more. I still have no idea why the system’s limiting resolution was about a thousandth of an arc-second, or how this relates to the diameter of its main mirror (30 centimeters).

Still, the inadequacies of the book shouldn’t detract from the importance of the Hipparcos mission. Virtually every subfield of astronomy now rests upon a firmer foundation, thanks to Hipparcos.

As an American, I can’t help but notice the differences between Hipparcos and the many equally impressive science missions carried out by NASA. Hipparcos produced no pretty pictures, and made no sudden discoveries. You can’t convey its importance in a ten-second sound-bite. It was designed, built, launched, operated, and funded by people who were focused not on short-term payoffs but on the long-term advancement of science. Such a mission would never have been supported by NASA, an agency that is forced to put glamor ahead of science because its budget is continually threatened by the whims of politicians. Of course, an advantage of the American system is that NASA has become very good at making its results accessible to the general public.

Ironically, it may not be long before the importance of the Hipparcos mission is merely historical. Encouraged by its success and the progress of technology over the last two decades, the ESA is now preparing a successor mission called Gaia, scheduled for launch in late 2012. If all goes as planned, Gaia will measure the positions of a billion stars, with an accuracy a hundred times greater than that of Hipparcos. Its completed three-dimensional star map will stretch across most of the Milky Way galaxy, far beyond the most distant naked-eye stars. Gaia will also discover thousands of planets orbiting distant stars, as well as tens of thousands of asteroids within our solar system. It will gather data over a period of five years, and its results will be published by 2020.

How to Photograph the Milky Way

This summer I’ve been making quite a few wide-angle astronomical photos, especially of the Milky Way. Here are links to a collection of photos taken in June in the San Rafael Swell, and some other miscellaneous astronomical photos.

When I show these photos to people, they often ask how to make similar photos themselves. Here’s a summary of what I’ve figured out so far. For much more advice on astrophotography, I highly recommend Jerry Lodriguss’s site.

To photograph the Milky Way, you need the following:

• A camera. I use Canon’s cheapest digital SLR, the Rebel XS (street price $500). Any other DSLR will probably work fine, except perhaps some of the earliest models which have higher noise levels. There may now be some high-end point-and-shoot cameras that will give acceptable results, but I’m not sure of this; most point-and-shoot cameras can’t take long enough exposures, and even if they could, the noise levels would be unacceptable. Film cameras don’t work well because even the fastest readily available films aren’t as sensitive to dim light as the sensor in a DSLR.
• A wide-angle lens. I’ve invested in a Sigma 20mm f1.8 lens ($520), although the inexpensive 18-55mm zoom lens that came with my camera was good enough to get started. If money is no object, get the Canon 24mm f1.4 ($1700), along with a full-frame Canon 5D ($2500); that’s what the pros seem to use, as far as I can tell.
• A tripod. I got a perfectly usable one at a discount store for $29.
• A dark site. This is the most difficult part for many people. You cannot make decent photos of the Milky Way from a light-polluted city. But here in Utah, there are some very dark sites within a one-hour drive of my urban home. Depending on where you live, you may need to travel farther.

Of course, you also need a clear sky with a view of the Milky Way. From the northern hemisphere, the best views of the Milky Way are in the summer, with the brightest parts in the southern sky.

Before heading out on a dark night, practice with the settings on your camera. Put it in fully manual mode, including manual focus. Set it for a 30-second exposure at ISO 1600, with the lens at its widest aperture (perhaps f3.5 on a zoom lens). Practice turning the display on and off, and turn its brightness down. Set the camera to store images in “raw” format, rather than jpeg. Most importantly, figure out how to manually focus the lens at infinity. Some lenses are conveniently labeled for focusing, but my zoom lens isn’t, so I had to mark the infinity setting (when zoomed out to 18mm) with white tape.

With this preparation, taking the photos should be pretty easy. Turn the display off when you’re pointing the camera (so it doesn’t ruin your eyes’ dark adaptation), then turn it back on to check the settings (30 seconds, ISO 1600, widest aperture) and fire away. It’s hard to compose a photo in the dark, but you can review the composition on the LCD and try again as needed.

After downloading the photos to your computer, use the software that came with the camera to adjust the brightness, contrast, and color balance. With “raw” images you can make some pretty dramatic adjustments without losing quality.

Speaking of quality, there are three factors that limit the amount of detail in a photo of this type:

1. Digital noise, which gets worse at higher ISO settings;
2. Lens aberrations, which blur and dim the edges of the image, and which get worse when the lens is opened to a wide aperture (low focal ratio);
3. The earth’s spinning motion, which turns star images into trails and blurs the Milky Way over time. (In 30 seconds the earth turns by 1/8 of a degree.)

To lessen any one of these problems, you generally need to worsen one of the others. The trick is to make sure that no one of them is much worse than the other two. By all means, experiment with different ISO settings, apertures, and exposure times. I always stop-down my Sigma lens to about f2.8 to reduce aberrations, but stopping-down may not be an option if you’re using a relatively slow zoom lens. I’m happy with ISO 1600, which is the highest setting on my camera. Most of the digital noise disappears when I reduce the photos to screen size, but in long exposures there are always some “hot pixels” which can be manually fixed in Photoshop if necessary.

Even with the most expensive equipment, photos made in this way will not be sharp enough to withstand poster-size enlargements. For example, I’m a big fan of Wally Pacholka’s photos, and I have a framed 36-inch panorama of his in my living room, but it doesn’t show much more detail at that size than in the screen version on his web site.

It’s a nice touch to include foreground scenery in your photos, but if you want more than silhouettes, you’ll need to plan carefully. A small amount of artificial light, from ambient light pollution or even a flashlight, can sometimes illuminate the scenery without ruining the Milky Way. Moonlight is another option, but anything bigger than a crescent moon will brighten the sky too much for a good Milky Way photo, and there are only a few nights each month, and a few hours each of these nights, when the crescent moon is above the horizon after dark. Even then, the moonlight won’t always be shining in the direction you want.

If you don’t want to include foreground scenery in your photos, then life becomes much easier. You can try using a tracking mount to compensate for the earth’s rotation, allowing much longer exposure times. Then you can use a smaller aperture and/or lower ISO setting to reduce problems 1 and 2 above. You can even use a film camera, which is far less expensive but requires additional skills and patience.

Detecting Bad Data

Political numbers geeks learned yesterday that Research 2000, one of the most prolific national political pollsters in recent years, may have been manipulating or even fabricating much of its data. This news comes less than a year after another national pollster, Strategic Vision, was exposed for probable fraud.

The evidence against these pollsters has come mainly from statistical scrutiny of their published results, performed by heroes like Nate Silver and Michael Weissman. But in most cases, you don’t have to be an accomplished sports statistician or a PhD physicist to detect bad data. You just have to care about numbers, and spend some time with them, and use a lot of common sense.

The sad thing is that in America today, hardly anybody cares about numbers except professional scientists and sports enthusiasts. Journalists, in particular, seem to think that their only job is to report both sides of the story--as if there’s no such thing as a fact. Except sports reporters, of course, who have to be extremely careful with facts and figures.

The good news, at the national level, is that the traditional media usually pick up the fraud stories after the bloggers do the actual work. The New York Times wasted no time reporting the Research 2000 accusations on its Caucus blog. If the accusations hold up, we’ll undoubtedly hear more. (Nate Silver will soon be assimilated into the New York Times. Let’s hope these kinds of stories don’t get suppressed in the process.)

Also, at the national level, there’s often enough honest fact-gathering that the frauds don’t make much difference. No single pollster had much impact on Silver’s bottom-line prediction of the outcome of the 2008 presidential election. The danger arises when everyone is relying on a single primary source, like the military or the White House.

At the local level, relying on a single authority is the rule rather than the exception. The Ogden Standard-Examiner almost always prints the word of local government officials as if it were fact, with no questions asked. Despite the detailed exposés on Weber County Forum, the Standard-Examiner has yet to report that the Ogden government manipulated its crime statistics, or that the government’s revenue projections for the Junction development were fraudulently overblown.

In science, fabricating data is the most serious of all crimes. I’ve given failing grades to astronomy students for fabricating their observations (which is usually easy to detect). There are continual allegations of fraud in medical research, where the financial stakes are incredibly high. Fortunately, the list of significant and documented cases of fraud in the physical sciences is extremely short. Although we physical scientists are just as human as everyone else, we know that our peers will tear our work apart if it doesn’t hold up to scrutiny.

APOD Celebrates 15 Years

Astronomy Picture of the Day, one of the very best sites on the Web, is celebrating its 15th anniversary today. My heartfelt thanks go to its devoted authors and editors, Robert Nemiroff and Jerry Bonnell--and to NASA for hosting the site.

APOD’s diversity is remarkable. The pictures include straight photographs, highly processed digital images, graphs, and even paintings. They come from professional astronomers, NASA, dedicated amateurs, scientifically inclined artists, and historical archives. The subjects go beyond pure astronomy to include the space program, earth science, and physics. Each picture comes with a short lesson, written by the editors, full of hyperlinks for those who want to learn more.

Although APOD is pitched to the general public, it’s also extremely useful to those of us who teach introductory astronomy, and to any scientist who needs a daily dose of breadth in this era of hyper-specialization.

Among Web sites, APOD is also remarkable for its simplicity: No banners, no sidebars, no drop-down menus, no fancy fonts. This is the Web as it was originally meant to be, where content takes precedence over presentation, and the hyperlinks are inserted by real human beings. The most noticeable change since 1995 is that the pictures have gotten bigger. They’ve also added Javascript rollovers to annotate some photos, and even an occasional video. And there’s now a linked forum where you can discuss the pictures. But simplicity still prevails.

Collected Works from Weber County Forum, Volume 2

About a year ago I posted a list of my Weber County Forum articles (loosely defined) over the previous three years. Since then the list has approximately doubled in length, so it's time for an update. Here, then, are my contributions since the middle of last June, in reverse chronological order:

• New Developments On and Around Malan's Basin Property (8 June 2010)
• Powder Mountain MOU Hearing Live Blogging (1 June 2010)
• Roosters Celebrates 15 Anniversary (14 May 2010)
• A Sunday Tour of Downtown Ogden (10 May 2010)
• Ogden City Miscellany (9 May 2010)
• 100 Ride in Damp Tour de Drome (1 May 2010)
• Mayor Vetoes Searchlight Ordinance (23 April 2010)
• Ogden's Transit Choices (6 April 2010)
• RAMP Funds Dog Park and Adventure Park, Not Velodrome (27 March 2010)
• Standard-Examiner: 36th Street Tank Closer to Reality (15 February 2010)
  
• Herbert Can Get More Than $10,000 for Political Favors (11 February 2010); follow-up (19 February 2010)
• Live-Blogging the City Council Water Tank Decision (2 February 2010)
• Ogden City Council Report (15 December 2009)
• Standard-Examiner: Candidates' Final Reports Filed (11 December 2009)
• Standard-Examiner Letter: Many Ethical Breaches in Ogden (3 December 2009); follow-up (11 December 2009)
• Live-Blogging the Streetcar Stakeholder Meeting (19 November 2009)
• Standard-Examiner: City OKs Use of Eminent Domain (19 November 2009)
• Bits and Pieces from Last Night's Emerald City Council Meeting (18 November 2009)
• Lifties and Smarties (13 November 2009)
• Is Candidate Mark Hains in Violation of Finance Disclosure Ordinance? (30 October 2009)
• Standard-Examiner: Tax Increment District Extended (14 October 2009)
• Live-Blogging City Council Decision on Junction Tax Increment Extension (13 October 2009)
• Be Honest, Fair, and Conservative (12 October 2009)
• Brief Report on City Council Candidates Forum (6 October 2009)
• Standard-Examiner Editorial Board Afraid of Mayor (28 September 2009); follow-up (3 October 2009)
• Saturday Evening News Roundup (19 September 2009)
• Vision Meets Reality (25 August 2009)
• The Junction: What Next? (7 August 2009)
• Live-Blogging the Big Veto Override (4 August 2009)
• The Junction -- A Good Investment? (29 July 2009)
• Junction 101 (27 July 2009)
• Live-Blogging the Transit Management Committee Meeting (9 July 2009)
• Scott Schwebke Fleshes Out the Budget Veto Story (9 July 2009)
• Court Orders Ogden to Explain Status of Missing Records (7 July 2009)
• Live-Blogging from the Planning Commission Chamber (1 July 2009)
• The Ogden City Run-Around (27 June 2009)
• Live-Blogging from the Emerald City Planning Commission (17 June 2009)

Purge Your Myrtle Spurge

Today’s Salt Lake Tribune has an article about a plant that’s been invading Ogden’s foothills over the last few years. Now I finally know what it’s called: myrtle spurge, euphorbia myrsinites.

A native of southeastern Europe and Asia Minor, myrtle spurge has made its way into Utah’s gardens as an easy-to-grow xeriscape plant. But it is also extremely invasive, spreading into natural areas and crowding out native vegetation. Now that we know the danger, we need to get rid of this enemy before it propagates any further. (Colorado has already banned myrtle spurge; Utah is still a little behind the times.)

Fortunately, myrtle spurge is easy to recognize and to uproot. Look for the low-growing succulent plant with gray-green leaves and yellow flowers and bracts at the tips of the stems. Being sure to wear gloves, gather up the multiple stems in both hands and firmly pull the plant up by its root.

You need to wear gloves, because the sap of the plant can cause a severe allergic reaction in some people. Be sure to wash your hands after touching it, and avoid touching your eyes. A reaction is especially likely in people who are allergic to latex.

This morning I made a good first dent in the myrtle spurge infestation just above the top of 27th Street. If a few others help out and we keep following-up, I’m sure we can purge it from this location. I’ve also seen it growing along the Mt. Ogden Exercise Trail, and I’m told it’s widespread in Ogden Canyon. I don’t know if it’s still feasible to eradicate it from Weber County, but now is the time to try.

And whatever you do, don’t plant this noxious weed in your yard! 

Science and Nature Reading List

Now that school’s out, it’s time for summer reading! Here are a dozen of my favorite science and nature books, recommended to students, colleagues, and friends alike. None of them are especially recent, and in fact, many are books that I first read for fun during graduate school, when I should have been working on my thesis. They’re listed below in approximate order by difficulty, starting with the lightest reading and ending with books that require some effort. None, however, assume any specialized background. Of course there are hundreds of other good science and nature books out there, most of which I haven’t read. I can’t promise that you’ll like all of these as much as I do, but I can promise that each of them is of the very highest quality.

• Encounters with the Archdruid by John McPhee. In this classic from the golden era of environmentalism, McPhee arranges for Sierra Club hero David Brower to spend some quality time with three of his natural enemies: a mining geologist, a resort developer, and a dam builder.
• Desert Solitaire by Edward Abbey. Essays by a hard-nosed realist about the wonders of southern Utah: juniper trees, snakes, clouds, heat, quicksand, tourists, inhabitants, and the encroachment of industrial civilization.


• The Cuckoo’s Egg by Cliff Stoll. My favorite mystery, and all true! A Berkeley hippie astronomer and computer geek discovers that a hacker is breaking into U.S. Government computers. Soon he’s teaching the FBI, CIA, and NSA all about internet security.
• Voodoo Science by Bob Park. An entertaining survey of perpetual motion machines, cold fusion, human space flight, and other things that look like science but aren’t. Written in the same spirit as Martin Gardner’s classic, Fads and Fallacies.
• Basin and Range by John McPhee. The best geology book ever written, which just happens to be about the place where I now live. Filled with clever juxtapositions of human and geologic time. The three sequels are also good: In Suspect Terrain, Rising From the Plains, and Assembling California.
• First Light by Richard Preston. Before the author became famous for writing The Hot Zone, he spent some time hanging out at Palomar Observatory and wrote this delightful book about the astronomers working there.
• 365 Starry Nights by Chet Raymo. Among the hundreds of guides to the night sky, this is by far my favorite. It offers a mini astronomy lesson for each night of the year, with lovingly hand-drawn illustrations. Its only deficiency is the lack of an index, so I created one years ago.
• The Character of Physical Law by Richard Feynman. A set of seven informal lectures by the great theoretical physicist, just as relevant and insightful today as when they were first delivered in the 1960s. If you like this, you’ll also enjoy Feynman’s QED: The Strange Theory of Light and Matter, which presents four more lectures on quantum physics.


• Guns, Germs, and Steel by Jared Diamond. The big picture of human history and prehistory.
• The First Three Minutes by Steven Weinberg. Still the best book on cosmology, written soon after our understanding of the hot early universe became firmly established.
• The Copernican Revolution by Thomas Kuhn. This well-crafted classic on the history of astronomy reminds us that a moving earth was once just as much a threat to some peoples’ belief systems as evolution and global warming are today.
• Gödel, Escher, Bach by Douglas Hofstadter. A weighty masterpiece that interweaves art, music, logic, puzzles, puns, language, molecular biology, and artificial intelligence.