Skywatch - 2021 - 22

A PR IL | 2021

S

pring is here for the Northern
Hemisphere. Leo now stands high
in the south, and just on the other
side of the zenith - the point on the celestial sphere that's directly overhead, i.e.,
90° from the horizon - you'll find Ursa
Major, the Great Bear. If you're currently
admiring Leo, swivel around 180° to better see the Great Bear. You'll also have to
turn the map on page 25 so that the yellow "Facing North" text is at the bottom.
We've encountered Ursa Major
before, in January, when we mentioned
that the Big Dipper is an asterism, a distinctive pattern formed by a group of
stars within a constellation (an asterism
can also connect stars from several constellations, the Winter Triangle being
one example). The Big Dipper is one of
the most recognizable of all asterisms

22 SK Y WATCH 2021

Ursa Major, the
Greatest of Bears
One of the best-known constellations has a rich
and multi-faceted history.

since it's circumpolar (never sets below the
horizon) for observers at mid-northern
latitudes and farther north. Two stars of
the Dipper's ladle, Dubhe and Merak, are
known as the Pointer Stars and are useful
guides to the North Star in Ursa Minor
(the Little Bear - can you see why it's
also called the Little Dipper?). Draw a
straight line from Merak through Dubhe
and about five lengths later you'll arrive at
Polaris, the North Star.
Why the long tail? Take a look at the
stick figure that represents Ursa Major.
That's a mighty funny-looking bear. How
did such an incongruous creature arise?
Let's go back to Roman mythology.
One day while wandering in the forest,
Jupiter was smitten by the beauty of Callisto, a maiden who had lain down to rest
after tiring from hunting. This incensed

Jupiter's wife, Juno, and later when she
found out that Callisto had given birth
to a son, she immediately assumed
that Jupiter was the father. In retribution, Juno transformed Callisto into
a bear. Long after, Callisto (the bear),
overjoyed at seeing her son, Arcas
(many years after he'd been adopted),
joyously rushed over to him. Arcas,
thinking he was being attacked, shot
an arrow at the bear, but Jupiter
stopped the arrow's fl ight before it
could strike Callisto. Anticipating
Juno's wrath, Jupiter also transformed
Arcas into a bear, grabbed both
mother and son by the tail, and hurled
them into the heavens. The force of
doing so lengthened the tails of both
creatures (in Ursa Minor, the quadrangle represents the body of the bear

ROBERT GENDLER

The galaxies M81 (left) and
M82 (right) might look like
nothing more than smudgy,
fuzzy patches in binoculars,
so it's good to bear this image
in mind while you observe
- remind yourself that light
has taken 12 million years to
reach your eyes from these
striking objects.



Skywatch - 2021

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