Sky & Telescope - April 2019 - 45

Under the Stars by Fred Schaaf

ALDEBARAN
The orange eye of the
Bull appears to be associated with the Hyades
but in fact ﬂoats in front
of the open star cluster.

The Eye
of the Bull
Aldebaran delights us by being
visible also in springtime.

A K IR A FUJII

've written here before about the thrill
of seeing Capella low in the due north
in July from North Dakota. My ﬁrst
time was during the longest total lunar
eclipse in U.S. history, whose totality for
me was followed by a seemingly celebratory auroral display.
In the present column, I want to
consider a 1st-magnitude star that,
though much farther south than
Capella, is also a star for all seasons,
and almost all months. The star is
Aldebaran, usually regarded as a sight
of late autumn and winter. To help
prove its year-round status, I'm going to
discuss the special beauties Aldebaran
displays in a month we don't always
associate with it (April with Aldebaran)
and also a month we don't ever associate with it (July with Aldebaran).
Summarizing the amazing Aldebaran. Whatever time or date you see
Aldebaran, it's one of the most distinctive of all stars. It's the only very bright

star (magnitude +0.9) hanging in front
of a very bright star cluster (the Hyades, about twice as far from Earth as
Aldebaran is). It's the 1st-magnitude
star moving away from us much more
rapidly than any other - at 54 km/s,
faster than all but three of the more
than 300 stars brighter than magnitude
3.5. It's the star that shined the brightest in Earth's night skies of any star at
any time in the past 900,000 years or
so (besides, currently, Sirius) - and
brighter than all but two that will shine
in the next 5 million years. It's the
star that had a close encounter in our
sky with Capella more than 400,000
years ago (when Aldebaran outshined
Capella), and the two formed the most
spectacular double North Star in at least
millions of years. Aldebaran, an orange
giant, is also a vision of what our Sun
will become, but the future Sun won't
be as mighty - Aldebaran's mass of
perhaps up to 1.7 times that of the Sun

suggests a luminosity of about 425 times
current solar and a diameter around 44
times that of the current Sun.
Aldebaran in April. Aldebaran and
the Hyades, an arrowhead pointing
right when rising early on November
evenings, at dusk is now an upright V
preparing to set. Aldebaran is now also
part of a horizontal line with the Pleiades to its right, and Orion's Belt and
Sirius to its left. Most notably, Aldebaran (in some Aprils) is a target for Mercury and brilliant Venus. No nighttime
star that can be occulted by the Moon is
brighter than Aldebaran - and no such
occultation more beautiful than when
it happens in April with a slender, not
overbearingly bright, lunar crescent.
Aldebaran and the Moon's near
miss last July. July is the month when
Aldebaran emerges into morning twilight to encounter many planets and
lunar crescents. The grazing occultation
of Aldebaran by the Moon on July 10,
2018, was the last visible in a night sky
until 2033. I wasn't far enough north
to catch the graze, but the near miss
I observed was as beautiful as anyone
could hope for.
In the dusk the day before, I enjoyed
Venus and Regulus, less than 1° apart,
with naked eye and binoculars, while
hearing ﬁve or even six wood thrushes
singing near my house. About seven
hours later I went out and arrived at my
favorite local pond. There I saw in the
sky and reﬂected in the still waters the
11%-illuminated moon and, only about
4′ from the edge of its lower cusp, the
twinkling point of Aldebaran. Through
binoculars and a wide-ﬁeld telescope
that captured the main grouping of the
Hyades, the twinkling point was pulsing madly with every color, including
intense red - and was countered with an
exquisite earthshine on the Moon's night
side. As I watched, words of preposterous
but delightful poetry came into my head:
"With all my heart I hereby / Summon
the softly glowing gray ghost of the rest
of the Moon / And Aldebaran nearby."
¢ Contributing Editor FRED SCHAAF
welcomes your letters and comments at
fschaaf@aol.com.
sk yandtele scope.com * A PR I L 2 019

http://www.skyandtelescope.com

Sky & Telescope - April 2019

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