365DaysDate: April 7, 2009


Title: Can Visual Observers Still Contribute to Science?

Podcaster: Travis Searle, Rebecca Turner, Mike Simonsen

Organization: AAVSO

Description: There are those who claim the age of visual observers contributing to science is dead and gone. Certainly CCDs capable of more precision and all sky surveys at visual and other wavelengths have impacted the domain of the visual observer. But, is this the end of an era? Let’s examine the facts.

Bio: The AAVSO was founded in 1911 at Harvard College Observatory to coordinate variable star observations made largely by amateur astronomers. In 1954, the AAVSO became an independent, private research organization headquartered in Cambridge, Massachusetts.

Today, with members in 45 countries and over 15.5 million observations, the AAVSO is the world’s largest association of variable star observers. Membership in the AAVSO is open to anyone — professionals, amateurs, and educators alike — interested in variable stars and in contributing to the support of valuable research.

Today’s Sponsor: This episode of “365 Days of Astronomy” is sponsored by Clockwork.


Hi, and welcome to Restless Universe, the podcast of the American Association of Variable Star Observers. You can find us on the web at I’m Mike Simonsen.

Today, I’m going to address a controversial topic among amateur and professional astronomers. No other recent issue has brought out such strong sentiment and heated debate as the value of visual observations, now and into the future. There are those who claim that the age of visual observers contributing to science is dead and gone. In some areas of astronomy this may be true, but let’s talk about visual observations in variable star research.

So let’s frame the arguments and examine the facts.

Up until late in the 20th century the monitoring of variable stars was primarily the province of dedicated visual observers. Organizations including the AAVSO and BAAVSS have amassed millions of visual observations, which have been used by astronomers and researchers to analyze and predict the behavior of variable stars.

The two main reasons people insist the age of visual observing is dead or dying are electronic detectors, like CCDs, and all sky surveys.

There’s no denying that CCDs capable of more precision and all sky surveys at visual and other wavelengths have impacted the domain of the visual variable star observer.
But it’s not the end of the road. Visual observers will simply have to be more selective about what they observe if they want to make a meaningful contribution to science. There is still a lot the visual observer can do.

The argument for the superiority of CCDs begins with the fact that the results are more precise. A skilled amateur can measure a star’s brightness to within 1/100th of a magnitude or better using a CCD camera, compared to 1/10th of a magnitude for most visual estimates.

Also, an image creates an objective, verifiable record. Visual observations, can sometimes be unreliable, and are difficult to verify.

Another advantage is that with the same telescope, an electronic detector can record fainter stars than a visual observer.

Finally, the human eye can only detect light in a very narrow range of the electromagnetic spectrum. Electronic detectors can take images across a broad swath of the electromagnetic spectrum.

No wonder people are ready to proclaim visual observing dead!

Consider this:

Although the price of CCDs is gradually coming down it is still a far more expensive endeavor than visual observing. The CCD itself is only one of the many necessary components. There is also the expense of filters and filter wheels, computers, hardware and software.

The demand on the drive system of the telescope means a beefier, more expensive type of mount is required than for visual work.

Before accurate photometric measurements can be made, observers must master dark, bias and flat fielding as well as transformation coefficients and data reduction. Learning to operate the camera, hardware and software, and locating and tracking targets present challenges and a steep learning curve for CCD observers.

Together, these factors exclude many observers limited by financial means or technical expertise.

Visual observation’s main advantage is the ease with which it can be done. With minimal equipment and some basic training anyone can make variable star observations. There are plenty of bright variables that can be monitored with the naked eye or an inexpensive pair of binoculars. Telescopic observations do not require tracking, so less expensive telescopes, like Dobsonians, can be used.

This ease of operation opens the door to variable star observing to the greatest number of observers. We should also add here that visual observing can be a valuable training ground for new observers, even if they eventually end up using a CCD to make observations.

Another important fact is there are just too many variable stars, hundreds of thousands in fact, for CCD observers to monitor and measure them all every night. There may be tens of thousands of CCDs out there, but the percentage of observers who are actually pursuing variable star photometry is small compared to the total.

The sheer number, and distribution over the globe, of observers willing to make and report visual observations has resulted in excellent coverage of the behavior of hundreds of stars, with timelines extending back decades. These observations, when stored in a central repository, like the AAVSO International Database, have proven to be a valuable, scientifically useful set of data.

The other argument for ditching visual observation is the perceived threat of all sky surveys. Typically, these are automated telescope systems that cover huge portions of the sky each night, measuring millions of stars in a certain magnitude and color range, uploading their data and making the measurements available to professional astronomers or the public.

Several satellite and ground based surveys have already covered the entire sky. All-sky surveys are currently in progress in many wavelengths, and more are coming online in the future.

So how do these surveys impact visual astronomers?

Photometric or variability surveys that have run their course don’t really encroach on visual observers’ domain. Tycho and 2MASS yield very good photometric results in their respective ranges and band passes, but they are not ongoing efforts. Those experiments are over and no more data is being collected. NSVS contains information on millions of stars down to 14th magnitude, but it too is an experiment that has been discontinued.

The surveys having the most direct impact on the viability or usefulness of visual observations are those that are accurately measuring great numbers of stars on an ongoing basis now.

No survey exists at the moment that covers the entire sky every night in any band pass or to any limiting magnitude. For example, The All Sky Automated Survey (ASAS) has a cadence of about once every three nights or so. It has a useful range of magnitude coverage from around 8 to 13.5V, and it covers the sky from the South celestial pole to around +28 degrees in declination. This is really the only survey at the moment that has any impact on visual observers.

So anything north of ASAS-3 sky coverage is still a viable target for visual observers, in spite of the fact that ASAS is running a similar survey in the northern sky right now. There is no guarantee that data will ever become public.

There are a number of other surveys going, but the data is not publicly available, and until it is, these surveys don’t impact the visual observers usefulness at all.

No existing survey covers stars brighter than 8th magnitude, and individual CCD observers tend to avoid stars this bright. Stars that get this bright, or are always brighter than this, will remain good visual targets for a long time. Naked eye and binocular variables remain the domain of visual observers for now.

Similarly, visual observers with larger telescopes, able to observe stars fainter than 13th magnitude can still support science by covering the gap between the faint end of ASAS coverage and the bright limit of many of the new surveys coming online.

There are also plenty of targets for visual observers to monitor that require higher cadence of observations. A three day delay in notification of a rare outburst of a cataclysmic variable, or a precipitous fade of an R CrB type star, would cause valuable science to be lost. Monitoring cataclysmic variables, and other stars that can change rapidly, is still a valuable, fun and worthwhile visual observing program.

When a new nova occurs, or a cataclysmic variable goes into outburst, visual observers are often the first to see the event and post their discovery. The survey sites might take several days before re-visiting a particular field, long after the outburst occurs.

Until the entire night sky is surveyed continuously, visual observers will remain important for these targets. That’s one reason the AAVSO has emphasized observing cataclysmic variables over the past few years.

Most surveys don’t spend much time observing stars approaching conjunction with the Sun, nor do they adequately observe stars in the morning sky that are just coming out from behind the Sun. So observing stars that are setting soon after sunset or rising in the pre-dawn hours can also be fruitful territory for visual observers.

Surveys and variability studies can be data-mined to detect or study variable stars, but they do not produce the long-term light curves needed to provide useful scientific information on long period variables like Miras and RV Tauri type stars. As it happens, some of the most interesting stellar behavior in variable stars is that some of them change their periods or exhibit outburst activity over timescales of decades; much longer than the shelf life of a typical survey or experiment.

Arne Henden, Director of the AAVSO, recently wrote, “Surveys are unlikely to put the amateur astronomical community out of business. There are just too many square degrees of sky to cover, too large a dynamic range in object brightness, too many wavelengths of interest, and too many techniques to use.

However, each new survey tries to address one or more weaknesses in the current situation, and amateurs must learn to stay up with the times and to change their observing patterns to continue providing the best science with the equipment that they have.”

Whether you observe with a CCD or visually, is up to you. If you want to contribute to science and enjoy the heavens above, there are plenty of interesting variable stars to follow.

That’s all we have time for today. Join us next time when we discuss why astronomers are so interested in variable stars, and the impact variable star science has had on astronomy.

End of podcast:

365 Days of Astronomy
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