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S&T News Bulletin - Jan 27

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         SKY & TELESCOPE'S NEWS BULLETIN -- JANUARY 27, 1995
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POLARIS DOESN'T MISS A BEAT

If our pole star could speak, it might echo Mark Twain's famous words,
"The reports of my death are greatly exaggerated." Predicted to stop
pulsating last year, the star at the end of the Little Dipper's handle
instead seems on the rebound. Polaris is a Cepheid variable, a kind of
star that brightens and fades as it alternately swells and shrinks. Yet
while its period has remained roughly constant at 4 days, its variability
decreased in amplitude from 0.1 magnitude at the turn of the century to
just 0.01 magnitude by 1992. This trend led a group of Canadian
astronomers to predict in 1993 that Polaris would soon stop pulsating
altogether. But new observations reveal that this didn't happen. Martin
Krockenberger and his colleagues at the Harvard-Smithsonian Center for
Astrophysics obtained high-resolution spectra of Polaris throughout much
of 1994. From the observed Doppler shifts, they found the star's
atmosphere still expanding and contracting every 4 days, reaching peak
velocities of 850 meters per second. At the winter meeting of the American
Astronomical Society on January 9th, Krockenberger explained that the
observed motions correspond to brightness changes of about 0.03 magnitude,
well above the level observed two years ago. "There's no sign that Polaris
has actually stopped pulsating," Krockenberger emphasized.

BLACK HOLE IN M106

Another important reult from January's AAS meeting came from radio
observations of the nucleus of M106, a bright spiral galaxy in Canes
Venatici.  An international team led by Makoto Miyoshi of Japan's National
Astronomical Observatory detected a thin ring of gas encircling the
galaxy's core.  The ring is only 1.5 light-years across, and it is
whirling around so fast -- 1,000 kilometers per second along its inner
edge -- that it would fly apart unless held in place by a dense central
object with a mass of some 36 million Suns.  This unseen object is almost
certainly a massive black hole, because its inferred density is orders of
magnitude higher than that of any known star cluster.

SPOTTING CERES

This week will perhaps be your most favorable chance in spotting the
largest asteroid, Ceres.  The 910-kilometer-wide minor planet should be
about magnitude 7.0 as it reaches opposition on February 3rd. Ceres will
also reach the closest point in it's orbit around the Sun -- called
perihelion -- in April.  These two closely spaced events, when added to
the asteroid's high declination make it a prime target. To find Ceres as
it makes its way through northern Cancer, consult the chart on page 78 of
the February SKY & TELESCOPE.

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   *------------------------------------------------------------*
   | Stuart Goldman         Internet: sgoldman@cfa.harvard.edu  |
   * Associate Editor                 mrastro@aol.com           *
   | Sky & Telescope                                            |
   * P. O. Box 9111           Sky & Telescope: The Essential    *
   | Belmont, MA  02178           Magazine of Astronomy         |
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