Sky & Telescope - October 2020 - 49

Mars in 2020

22
21

Nearest Earth
Oct. 6

20
19
18
17
16

-3.0

15
14

-2.0

-1.5

d
itu

Opposition
Oct. 13

Magnitude

-2.5

-1.0
-0.5
0

15 25
June

15 25
July

13
12

Apparent diameter (arcseconds)

at a declination of slightly greater than
+5°, which is a full 30° higher than
during its 2018 opposition. Size-wise,
the planet swells to 22.6″ this time
at closest approach (on October 6th),
compared with the 24.3″ it achieved
during the last go-round. Get your
scope tuned up and clean your eyepieces
because Mars won't be this close again
until 2035.
Surface highlights. The Martian
south pole nods 20.4° earthward this
opposition, offering spectacular views
of the feature-rich southern hemisphere, including the South Polar Cap
(SPC). Martian southern hemisphere
summer began on September 3rd, so
much of the cap's frozen carbon dioxide
has vaporized into the planet's thin
atmosphere. Still, on steady nights with
a 6-inch or larger telescope used at high
magniﬁcation, you should nevertheless
be able detect a remnant of the SPC's
former expanse.
While the North Polar Cap (NPC) is
tipped out of view it should be easy to
spot the lens-shaped North Polar Hood
(NPH), located along the northern limb
of the Martian disk. Comprising clouds
that huddle over the planet's north
polar region in winter and early spring,
the NPH is often so bright that beginning observers understandably confuse
it with the NPC.
Martian surface markings make the
planet both a joy and a challenge to
explore. Mars rotates once every 24.6

11
10

4 14 24 3 13 23 3 13 23 2 12 22 2 12 22 1
August
September October November December Jan.

hours, nearly the same rate as Earth.
That means features drift 9.5° of longitude toward celestial east each passing
night. So, if you observe the planet
around the same time each night you'll
notice that a given marking gradually
slides eastward. Any marking seen on a
particular night at a speciﬁc time will
return to that spot at the same time
41 days later. An orange eyepiece ﬁlter
(Wratten #21) will help the dark markings stand out better against the bright
desert regions.
Let's take a quick tour of the most
prominent features, starting with
the thumb shape of Syrtis Major, an
ancient shield volcano composed of
dark basaltic rock. Like a low, thick
branch extending from the trunk of a

tree, Mare Tyrrhenum reaches to the
south and west of Syrtis, ending at a
bright gap called Hesperia, which separates it from the dark garland of Mare
Cimmerium.
Follow the arc of Cimmerium and
you'll arrive at a short, dark stripe
called Mare Sirenum, the most prominent albedo feature on the planet's
"boring" hemisphere, where easy-to-see
formations are few and far between. A
cursory glance may reveal nothing but
a bland orange desert extending all the
way to the NPH; however, if you look
more carefully you might just spot one
of the solar system's biggest volcanoes,
Olympus Mons. Towering 25 kilometers
above the surrounding desert and covering an expanse about the size of France,

-60°

Deucalionis Regio
SINUS
US
SABAEUS MERIDIANI

S IN

+60°
180°

200°

220°

Protonilus

260°

280°

300°

Ismenius Lacus

320°

S
RA

B
A

NILIACUS
LACUS

UTOPIA

240°

Achillis
Fons

IA
R

Nodus
Alcyonius

Juventae Noctis
Lacus
Fons

CHRYSE

REN

-40°
UM

-20°
Phoenicis
Lacus

AMAZONIS

340°

0°

MARE
ACIDALIUM

20°

Idaeus
Fons

0°

THARSIS
Olympus Mons

ARCADIA

+20°
+40°

Hyblaeus
Extension

MARGARIAURORAE
TIFER
Tithonius
SINUS
SINUS
Lacus
Oxia
Palus

E SI

Solis
Lacus

Propontis

E
R

+40°

Trivium
Charontis

ELYSIUM

Sigeus
Portus

Claritas

Osiridis Pr.

+20°

Gomer
Sinus

MAJO

Cerberus I

SYRTIS

0°

YR
sp
IAPYGIA
RH
e
ENU
Tri ria
M
Si ton
nu is
s
LIBYA

TIS
PEN
FRETUM MARE ERYTHRAEUM
SER
NDORAE
PA
E
MAR

-20°

MA R

ELLAS

MARE CIMMERIUM

H
A
I A RE
TI
CU
M

M
DR

-40°

G R A PH: G REGG DINDER M A N / S&T; M A RS M A P: DA MIA N PE ACH /
G REGG DINDER M A N / S&T

T Use this map to locate key surface features on the Martian surface. South is presented up to match the orientation in Newtonian reflector telescopes, as well as refractors and Cassegrain instruments used without a right-angle diagonal.

40°

M A R E
60°

+60°

B O R E U M
80°

100°

120°

140°

160°

180°

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Sky & Telescope - October 2020

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