The Sperling Files: The Dim, the Weak and the Ugly

Norman Sperling

(c) 2002 Norman Sperling. Excerpted with permission from "What Your Astronomy Textbook Won't Tell You" (ISBN 0-913399-04-3).

How does a researcher select what to research? How does an editor select what to publish?

In both processes, the humans involved are often attracted to bright and beautiful objects. For the researcher, “bright” means plenty of light is available, making it practical to take detailed photographs and spectra. For the picture-editor who has to select some items and leave out others, bright and beautiful objects beat dim and ugly ones.

This means that the results reported in textbooks, the press and research journals are not a fair sample.

Red Dwarf Stars

The most abundant type of star seems to be the red dwarf. It's certainly the most abundant type within 25 light years. The very closest star to the Sun, Proxima Centauri, is a red dwarf – but so dim that you need a telescope to see it. Even the brightest red dwarf is too dim to see without binoculars. Since red dwarves are very difficult to recognize, and hardly any are known.

For all their abundance, they aren't studied by very many researchers. Compared to other types of stars, they're dimmer, so there is less light to study. They are generally thought to not do much, other than sporadic unpredictable flares, so there is little of interest to attract researchers.

If red dwarves were studied as intently as, say, white dwarves or red giants, would more interesting things be discovered about them?

Thin Nebulæ

Bright, thick nebulæ get lots of attention. For active nests of stars, for beautiful twists and knots, they look great. There are lots of thinner, dimmer nebulæ cataloged, but only a few observers track them down. Mostly, thin, dim nebulæ get ignored.

If thin nebulæ were studied as much as thick ones, would more interesting things be discovered about them?

Dwarf Elliptical Galaxies

In nearby clusters of galaxies, the most abundant galaxy type is the dwarf elliptical. To see even the brightest requires a significant telescope. Beyond 50,000,000 light years, dwarf ellipticals are very difficult to recognize. Because they are small and faint, not many are known.

For all their abundance, they aren't studied by very many researchers. Compared to other types of galaxies, they're dimmer, so there is less light to study. They are generally thought to not do much, having little nebulosity and no big powerful stars, so there is little of interest to attract researchers.

If dwarf ellipticals were studied as intently as, say, spirals or giant ellipticals, would more interesting things be discovered about them?

With Galaxies, as With People,

Pictures Show the Most Attractive,

Not the Most Typical.

People who select illustrations for books, slide sets, and other media naturally tend to pick the most attractive examples. This leads to some important misunderstandings. People looking at the examples tend to think they're typical, when actually they are not.

“Spiral” galaxies, which physically are disc galaxies, are prettiest to most humans. Therefore, the prettiest spirals show up in books and slide sets a lot more than others do. Ragged and less-symmetrical spirals, and elliptical and irregular galaxies, hardly ever get selected, even though ellipticals are very abundant.

Most textbooks include a photo of the beautiful galaxy M 51, the “Whirlpool.” This is the galaxy with the most obvious spiral appearance; smaller telescopes (perhaps 35 cm) will reveal its arms better than any other galaxy's. Many books call M 51 “a typical spiral galaxy.” It is actually one of the least typical! Very few disc galaxies have continuous arms that can be traced so far around. Hardly any other bright galaxy has such vivid arms. Enjoy the beautiful view, but don't swallow the claim that it is “typical.” It isn't, which is why so many books include it. More typical galaxies don't look as handsome. Editors select the nicest-looking pictures, therefore making the selections anything but “typical.”

Barred spirals, too, rarely look like their “typical” case, NGC 1300. That one, again, looks prettier and cleaner than most. That's a good reason to publish its picture, but it's wrong-headed to call it “typical.”

Much the same applies to planetary nebulæ, pre-stellar nebulæ, and surface features on planets. Editors (and often researchers) select the brightest and most attractive ones. Dimmer and less-attractive examples may be more typical, but they're less-often studied and shown.

Norm Sperling is editor of The Journal of Irreproducible Results. Previously he was assistant editor of Sky & Telescope magazine and Science Editor at AltaVista.com. Norm teaches astronomy in universities around San Francisco, wrote the new book "What Your Astronomy Textbook Won't Tell You," and co-designed Edmund Scientific's Astroscan telescope.