Sky & Telescope - June 2020 - 43

θ

ι
URSA MAJOR

Facing

DRACO
3

ε

+60°

lar vie w

6

R

AU

N
W

IG

A

CAME

LOPA
RDA

LIS

α

β

D

α
Regulus

α

M
M oo
ay n
29

Denebola

TA N

S

α

β

C
BER OMA
ENI
CES

β

α

γ

LEO

M51

CANES
VENATICI

an

+60°

SEX
α

α

O

R

U

S
γ
δ

C

C

V

R

C

I P

E

E

L

IC

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Sp

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T

A

I R
V
n
o
Mo e 2
Jun
ica

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RA

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Sickle

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ub

EN
UT S
)

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h

9

o
Virg ter
s
Clu

ε

The Horse and Rider
Facing West

γ

Arcturus

Binocular Highlight by Mathew Wedel

M67

δ

δ

Th

α

ig er
p
ip

α

β

M4

4

A
S R
R JO
U A
M

α

β

B

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LE OR
IN
M

+80°

M

M3

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ER
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81

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CANES VENATICI

G

Polaris

r
iza or
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&

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M oon
May 2
6

Po

N

OÖTES

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x
llu

L

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M

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IN

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θ

κ

Ca

BOÖTES

r

5°

HD 116798

ocu

Mizar

M101

bin

n
ci
a
F

g

h

β

Alcor

α

12h
β

-40°

5h

g South

US
UR
TA
N
CE

SW

β

g

γ

n
ci
Fa

WHEN TO
USE THE MAP

Late April
Early May
Late May
Early June
Late June

2 a.m.*
1 a.m.*
Midnight*
11 p.m.*
Nightfall

*Daylight-saving time

have shown Mizar and Alcor - the "Horse and
Rider" in Ursa Major, the Great Bear - to hundreds if not thousands of people at star parties and
outreach events. And for just that reason it never
hurts to brush up on the fundamentals.
Mizar and Alcor are roughly 80 light-years
away, but the parallax distance measurements
have large margins of error. We are certain the two
stars - or rather, the two systems - are moving
together through space as members of the Ursa
Major association. But after almost four centuries of
study, it's still unclear if they're orbiting each other or
not. If they are gravitationally bound, it's a long orbit,
taking 700,000 years or more to complete.
I mentioned that Mizar and Alcor are systems, not
single stars. Mizar is at minimum a quadruple-star
system and Alcor is at least double. You probably
already know about Mizar, since splitting the two
brighter and wider components is a favorite trick with
small telescopes or big binoculars. Mizar A and B are
separated by 14″, which is doable with 20× tripodmounted binos but very tough with any less magnification. If you haven't split Mizar, grab your big glass
and see what you can do.
While you're in the neighborhood, check out
HD 116798, a yellow-white star a bit south of the line
between Mizar and Alcor. At magnitude 7.6, it should
be visible without optical aid to the eagle-eyed and
an easy catch in binoculars. In 1722, German theologian and scientist Johann Georg Liebknecht named
the star Sidus Ludoviciana, thinking it to be a planet.
Liebknecht was mistaken about that, but he studied
both fossils and astronomy, so he's okay in my book.
¢ MATT WEDEL loves contemplating the night
sky on dinosaur digs in Oklahoma and Utah. He's
probably out there right now.
sk yandtelescope.org * JUNE 2 02 0

43


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Sky & Telescope - June 2020

Table of Contents for the Digital Edition of Sky & Telescope - June 2020

Contents
Sky & Telescope - June 2020 - Cover1
Sky & Telescope - June 2020 - Cover2
Sky & Telescope - June 2020 - 1
Sky & Telescope - June 2020 - Contents
Sky & Telescope - June 2020 - 3
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Sky & Telescope - June 2020 - Cover3
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