杏吧原创

TOM DROEGE has a formidable reputation in the world of big science. He built
the electronics for the CDF experiment, which found the top quark at Fermilab
three years ago. When headlines were being made by a 鈥渃old fusion鈥� device that
reputedly generated more energy than it took to run, he was the unanimous choice
of physicists to investigate the American company making the claims. But in all
his 35 years as an electrical engineer and instrument designer Droege has never
been involved in a project quite like this.

The Amateur All-Sky Survey, TASS for short, is a programme to continuously
monitor a large portion of the night sky in the hope of finding objects that
change their brightness, such as variable stars, novae and supernovae. Though
it鈥檚 an ambitious task, the equipment seems pretty basic. The telescopes
involved are little more than camera lenses equipped with sensitive electronic
light detectors, and they are small enough to fit in the palm of your hand. But
the really unusual thing about the project is the way it鈥檚 organised. There are
no meetings. There is no budget. And no one is in charge. Everything is done
through the Internet. 鈥淢ore than half the people I work with I鈥檝e never met face
to face,鈥� says Droege.

The origin of the TASS project can be traced back to the early 1990s, when
Droege鈥檚 team completed the electronics for the top quark detector at Fermilab,
the high-energy physics centre near Chicago. 鈥淥nce we鈥檇 built the equipment, the
lab mothballed us,鈥� says Droege. 鈥淭hey forbade us to work on anything else.鈥�
Bored and frustrated, Droege threw himself into a succession of time-filling
projects, including a cold fusion experiment carried out with his metallurgist
brother in the basement of his home in Batavia, near Chicago. Then in the summer
of 1994 came the collision of Comet Shoemaker-Levy 9 with Jupiter. The event
caught Droege鈥檚 imagination and inspired him to begin building a comet detector.
鈥淏efore that I had no interest in astronomy,鈥� he says.

Droege turned to the Internet to ask astronomers what they thought of his
idea. The answer that came back was that he should forget looking for comets and
instead turn his attention to a far more valuable project: the search for
variable stars. Thus was TASS born.

It鈥檚 a clever idea, making use of the way that amateur astronomers can cover
much wider regions of the sky than their professional counterparts.
Professionals spend most of their time zooming in on smaller and smaller
portions of the firmament with bigger and bigger telescopes. But for many
aspects of astronomy you don鈥檛 have to have great detail. What you need is to
cover as much of the sky as possible. 鈥淎 tiny TASS telescope views an area of
sky a million times bigger than the Hubble Deep Field picture of galaxies,鈥� says
Droege. 鈥淚t鈥檚 possible all kinds of celestial objects have been overlooked.鈥�

So far, Droege has shipped camera equipment to 9 sites around the US and
Canada. 鈥淏asically, they鈥檝e gone to anyone who sent me an e-mail indicating they
would be willing to operate a system and write some of the software,鈥� he says.
鈥淚f anyone wants to join us, all they have to do is look up the TASS website.
There is no membership fee. You are a member if you want to be.鈥� Over a year,
the telescopes at the 9 TASS sites should accumulate 200 measurements on each of
100 000 stars down to magnitude 13.5鈥攁bout a thousand times fainter than
would be visible with the naked eye.

TASS has the potential to discover at least a thousand new variable stars. In
fact, it has already confirmed that BP Virginis鈥攁 star suspected of
changing over time鈥� really is a variable. It could also reveal large
numbers of uncatalogued asteroids, including 鈥渒iller asteroids鈥� heading our way,
the afterglows of gamma-ray bursters, the rapidly varying nuclei of 鈥渁ctive
galaxies鈥� such as quasars and lots of other known and unknown objects. 鈥淲henever
astronomers take on a project with a much higher data rate, lots of interesting
discoveries are made,鈥� says Bohdan Paczynski from Princeton University, New
Jersey.

Take novae. These stellar explosions occur in binary systems when one star
dumps so much matter onto its companion that it becomes unstable and explodes.
They can go unnoticed for days or even weeks. 鈥淚f we got measurements for the
first three weeks showing how a nova developed, that would be fantastic,鈥� says
Paczynski, a renowned astronomer and a keen supporter of Droege鈥檚 project. 鈥淭he
earlier you catch this kind of thing happening the more scientific information
you have.鈥�

Paczynski points out another important application of the all-sky searches:
the creation of an archive. 鈥淭his gives astronomers the capability to trace
back the variability of any interesting objects they discover in the future,鈥� he
says.

Droege鈥檚 original comet-hunting instrument was built with three camera
lenses, bought for $19 apiece in a New York camera store. Each lens looks
in a fixed direction, and the light it collects falls onto a fax
chip鈥攚hich is simply a line of electronic light detectors. As the Earth
turns, the night sky is drawn across the chip, allowing a computer to read out
its pattern of stars and nebulae a line at a time. 鈥淭he principle is the same as
copying a document with a fax machine,鈥� says Droege. 鈥淥nly in this case the
document is the night sky.鈥�

During a typical 8-hour night, a camera lens captures a band of sky 120
degrees long and 3 degrees wide centred on the celestial equator. The ability of
the instrument to detect a comet depends on having three lenses, each equipped
with its own fax chip, pointing 15 degrees apart. Since the Earth rotates
through 15 degrees every hour, this ensures a 1-hour time lag between the images
recorded by adjacent cameras. 鈥淚n an hour a comet can move just enough against
the stars to give itself away,鈥� says Droege.

But images of the sky taken one hour apart can equally well reveal a
difference in an object鈥檚 brightness as a difference in its position, so the
instrument is ideally suited to spotting variable stars as well as comets. In
the latest version, the Mark III, Droege has replaced the fax chip with a
charge-coupled device (CCD) which has an array of 768 by 512 pixels. It can
follow a star for longer, soaking up more of its light, and so is sensitive to
fainter objects.

Number crunching

From the start, Droege realised that building the hardware for TASS was the
easy part. The real problem was analysing the data. 鈥淚t was a mammoth software
project,鈥� he says. The way the software has been written highlights the peculiar
way the TASS collaboration is organised. 鈥淭echnically, we have laissez-faire
management,鈥� says Droege. 鈥淲e all talk a lot over the Internet about what we
might do. When there seems to be agreement on something, then someone will pop
up and say, 鈥業鈥檒l do that.'鈥�

It was necessary, for instance, to write the software to turn the 100 to 200
megabytes of raw data recorded by the Mark III on a typical night into a format
recognisable by the off-the-shelf image-processing programs used by professional
astronomers. Norman Molhant, a professional programmer in Montreal, Canada,
volunteered for the task. Then it was necessary to write the software to
recognise all the star-like objects and calculate their coordinates in the sky.
In stepped Michael Gutzwiller, an amateur astronomer and professional programmer
from Cincinnati, Ohio. Once the coordinates were known, the next pressing
problem was to look them up in star catalogues to identify the stars, a job
taken on by Michael Richmond, a professional astronomer at Princeton University
whose Mark III is set up at his parents鈥� home in Vermont. Richmond also took it
on himself to create the TASS web site on http://www.tass-survey.org/.

Droege estimates he has a core of about a dozen Internet collaborators
working full-time on the software project. 鈥淚t鈥檚 the equivalent in power of a
major university department, and just paying the wages of a group that big would
cost a fortune,鈥� he says. 鈥淲e鈥檙e doing a multimillion-dollar software project on
the cheap.鈥�

Cheap is relative of course. The 67-year-old Droege has already ploughed
about $100 000 of his own money into what he calls his 鈥渞etirement
project鈥� and he expects to stump up the same again before he is done. 鈥淚 am
carrying on a `gentleman scientist鈥� tradition that goes way back in astronomy,鈥�
says Droege. 鈥淚 am not rich. I just prefer to drive an old Toyota and do this
work rather than drive a fancy car.鈥�

Funding is one of the main reasons why the professionals have not done this
kind of project already. 鈥淚t鈥檚 a long-term project unlikely to produce results
quickly enough to satisfy funding agencies,鈥� says Richmond. 鈥淭hat鈥檚 the great
thing about TASS,鈥� says Paczynski. 鈥淭om provides his own funds. He doesn鈥檛 care
about the National Science Foundation or NASA.鈥�

But while Droege鈥檚 dollars are bank-rolling a large slice of the project, he
is not the only one putting his money where his mouth is. Paczynski, for
instance, has bought light filters and CCDs for TASS, and is hoping to set up
one of Droege鈥檚 detectors at the Las Campanas Observatory, high in the Chilean
Andes, where it can monitor the southern sky.

Droege鈥檚 Mark III telescope is operated from a rather less exotic
location鈥攁 shed behind his house. It has no moving parts and is totally
automatic. Droege is currently developing the 鈥渘ext generation鈥� Mark IV, a fully
automatic telescope to survey the whole sky. It will have five 400-millimetre f4
telephoto lenses and a 2048-by-2048 CCD chip with 15-micrometre pixels. The
larger chip will permit even longer exposures, making the instrument sensitive
to stars as faint as 15th magnitude. 鈥淲ith luck, we鈥檒l have the first Mark IV
ready by the end of the year,鈥� he says.

Droege has enough lenses for 20 Mark IV units, and has already found homes
for the first eight in the US and Chile. But he would love to get Mark IV
systems into the hands of people in Europe, Asia, South Africa or Australia, and
thinks having a Mark IV would be a wonderful project for a developing country.
鈥淗ere is an opportunity for a department long on talent but short on cash that
is unable to travel to a big observatory to gain experience,鈥� he says. 鈥淭hey can
have an instrument that would cost over $50 000 for free. They need only
have an Internet connection, follow the work, contribute, and so convince me
they will put the instrument to good use.鈥�

Up on the roof

Droege鈥檚 own Mark IV will go on the roof of a special extension added to his
home. He is revelling in doing science without the politics, bickering and
hassles that go with doing research the conventional way. 鈥淚n the beginning,
thousands of years ago, there were just associations of scholars,鈥� he says. 鈥淏ut
then we added bricks and mortar, fees and so on, and all these things got in the
way of pure scholarship. What we鈥檝e done is re-create that original association
of scholars.鈥� He calls it an 鈥淚nternet college鈥�. 鈥淚t鈥檚 an entirely new type of
collaboration,鈥� he says. 鈥淚鈥檓 more proud of the way I put together the
collaboration than any of the equipment.鈥�

鈥淚t鈥檚 the willingness to share everything that is one of the most important
facets of the project,鈥� says Richmond. 鈥淎mateur astronomers work for the fun of
it. They don鈥檛 need to get funding from the government, or publish enough papers
to be granted tenure. As a result, they are in many cases much more willing to
work together as a team, selflessly, than professional astronomers.鈥� Take the
way the results from the project are distributed freely over the Internet.
Droege has always insisted that the results should be available to everyone.
鈥淚t鈥檚 rare to find a scientist who is willing to put all his hard-earned data on
the Internet as soon as he gathers it,鈥� says Richmond.

When it comes to listing the advantages of the TASS way of working, Droege is
positively evangelical. 鈥淢any people pay good money and spend many years of
their lives to get a PhD,鈥� he says. 鈥淵ou will learn much of what a PhD programme
teaches by participation in TASS. We will give you everything but a paper
诲别驳谤别别.鈥�

Because he seeds the project by building cameras and giving them away, Droege
calls it the 鈥淔ield of Dreams鈥� school of science management. 鈥淚f you build
cameras, the software will come.鈥� Tinkering with the Mark IV electronics in his
cluttered workshop, Droege is clearly as happy as can be. 鈥淚鈥檓 having the time
of my life. I鈥檝e got interesting things to do and no one is competing with me,鈥�
he says. 鈥淭hese days I鈥檓 like a kid in a candy store.鈥�