Sky & Telescope - April 2021 - 43

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WHEN TO
USE THE MAP

Late Feb
Early Mar
Late Mar
Early Apr
Late Apr

Midnight
11 p.m.
11 p.m.*
10 p.m.*
Nightfall

*Daylight-saving time

ur subject this month is the Ursa Major Moving
Group, a set of stars traveling together through
space that were probably born from the same nebula. The Group includes all the stars of the Big Dipper
except the ones at the asterism's eastern and western extremes - Alpha (α) and Eta (η) Ursae Majoris
(Dubhe and Alkaid, respectively). Its center is about
80 light-years away, making it the nearest grouping
of stars to our Sun. The closest open cluster, the
Hyades, is almost twice as far away.
The bowl of the Dipper contains my favorite cosmic odd couple: M97, a nearby planetary nebula, and
M108, one of the more distant Messier galaxies. M97
is about 30 times farther from us than nearby Beta (β)
Ursae Majoris (Merak) - but at 47 million light-years,
M108 is roughly 20,000 times more distant than M97.
The Dipper doesn't include every member of the
Group, which is actually a stream of stars, spread out
across roughly half the sky. Other group members
above the horizon at this time of year include Gamma
(γ) Leporis and Beta Aurigae in the west, and Alpha
Coronae Borealis and Beta Serpentis, both rising in
the east. Try to pick them all out in quick succession,
and you may feel that a cascade of stars is racing
past, like a formation of jets at an airshow. Which, in
astronomical terms, is pretty much what's happening. In the small compass of human history, these
stars appear fixed in our skies, but on a galactic scale
they're just passing through.
I like to think of the cosmos as an ocean, and
Earthlings as tourists on a submersible. The stars,
nebulae, and galaxies flash by like shoals of fish, and
we press our eyes to the glass in wonder.
 MATT WEDEL likes to imagine that the night sky
is below him, not above him, and that he's at risk of
falling in. That hasn't happened. Yet.
sk yandtelescope.org * APRIL 2 021

43
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Sky & Telescope - April 2021

Table of Contents for the Digital Edition of Sky & Telescope - April 2021
