Sky & Telescope - March 2022 - 45

Evenings with the Stars by Fred Schaaf
Spring
Triangles
Three foes of Hercules bunch
in the evening sky.
W
e can make use of parts of three
constellations well placed on
March evenings to locate a marvelous
arrangement of rather compact
triangles. We'll be using the front
section of Leo, the Lion, the head and
heart of Hydra, the Water Snake, and
the cluster-filled center of Cancer, the
Crab. On our Northern Hemisphere
Map (pages 42 and 43), you can see
that the center of Cancer and the head
of Hydra are approaching the meridian
(the imaginary line that joins north and
south and passes directly overhead) and
the bright, western half of Leo is not
far behind. They're floating high in the
southeast and south at map time.
By the far the brightest of the three
groupings is the front portion of Leo. I
prefer the time-honored tradition that
sees Regulus, Alpha (α) Leonis, as the
heart of the noble Lion. That makes
the large hook of stars that extends up
(north) from Regulus the Lion's chest,
head, and mane.
The hook asterism is also well known
as the Sickle, a farming tool that has
Regulus as the bottom of the implement's
handle. The other bright star in
the Sickle (or Lion's mane) is Algieba,
Gamma (γ) Leonis. Algieba is best
known as a beautiful double star in
amateur telescopes, but to the naked
eye their combined brightness equals
a 2.1-magnitude point of light - just
a trace dimmer than Polaris and only
about half as bright as Regulus.
At magnitude 1.4, Regulus is the
dimmest of all 1st-magnitude stars, but
it's also the one closest to the ecliptic,
the Sun's apparent path through the
heavens and centerline of the zodiac.
That makes Regulus the 1st-magnitude
pCRABCENTRIC SKY VIEW Cancer, the celestial Crab, is front and center in this chart from
Alexander Jamieson's 1822 Celestial Atlas. Below the Crab is the head of Hydra, while Leo's
head and front paws are to the left.
star that has the most frequent closest
encounters with the Sun, the Moon,
and the planets.
Let's use Regulus as our starting
point for visiting some very interesting
triangles. One of these is an almostequilateral
triangle that connects Regulus
with 2nd-magnitude Alphard, Alpha
Hydrae - the heart of Hydra - and the
fairly dim but compact asterism that
forms Hydra's head. Whereas Regulus is
the blue-white heart of Leo, Alphard is
the distinctly orange heart of Hydra. At
magnitude 2.0, Alphard is almost identical
in brightness to Algieba and Polaris.
A fascinating fact is that for observers
near latitude 40° north, Alphard
and Polaris have the same altitude but
are in exactly opposite directions when
Alphard reaches the meridian. That
moment comes roughly two hours after
the times listed on our March all-sky
map. That same map shows that the
mostly dim constellation Hydra is so
expansive (the longest of all constellations,
measured west-to-east) that
its tail has not yet risen by the time its
head crosses the meridian.
Regulus and the head of Hydra also
form a triangle with the 3rd-magnitude
heart of Cancer, M44, the Beehive Cluster.
You can pin down its location with
another triangle made up of Procyon,
Hydra's head, and M44 itself.
Leo, Hydra, and Cancer have
something more in common. In
Greek legend, all three were adversaries
vanquished by the most famous of
strongmen, Hercules. Hercules killed
the Nemean Lion and the Lernean
Hydra. Cancer is reputed to have been
a monstrous crab that Hera, the queen
of the gods, sent to bite Hercules' toe.
The hero kicked the crab from his foot
all the way up into the heavens, where
we see it today. And on March evenings,
the constellation of Hercules is only
now starting to rise in the northeast.
¢ FRED SCHAAF observed both his first
total eclipse of the Sun and his first great
comet in March 52 years ago.
sk yand tele scope .o r g * MARCH 2022 45
ALEXANDER JAMIESON / CELESTIAL ATLAS (1822) / UNITED
STATES NAVAL OBSERVATORY LIBRARY / PUBLIC DOMAIN

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Sky & Telescope - March 2022

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