Sky and Telescope - July 2018 - 24

Mars Opposition

Your best strategy is to observe the planet as often as possible to maximize the chance of getting a sharp look during
infrequent spells of excellent seeing, when all dross falls away
and the planet looks as real as being there. Remember to
allow your telescope's optics to cool to the outside temperature, so they don't become their own source of "boiling" air.
Mars won't be this close to Earth again until September 2035,
a simple fact that motivates many a Mars-watcher to put eye
to eyepiece every clear night around opposition.
The Red Planet remains in Capricornus throughout the
summer and early fall, making a brief foray west into neighboring Sagittarius near the end of its retrograde loop in late
August. Minimum declination of -26° 33′ occurs on August
15th before the planet ﬁnally comes up for air in the middle
of October. When the kids knock on doors for Halloween
candy, Mars will still be in negative magnitudes, 12″ across,
and perched at declination -17°.

p SOUTHERN ICE The south polar cap, which reaches 3 km deep in
places, is made up of frozen water and carbon dioxide.

wary eye out for another polar cap look-alike, the 2,300-kilometer-wide impact basin Hellas. In June, Hellas may be still
be coated with frost or hidden under a blanket of clouds,
mimicking the appearance of a polar cap, but you can tell the
two apart - Hellas is distinctly north of the SPC and appears
duller. Even small scopes should provide great views of these
polar features.
To see all these wonderful features best, you'll need to
observe around the time of dawn when the planet is high
enough above the muck for a good look. Mars won't be conveniently placed for evening viewing until early August.

What to See
The south polar cap (SPC) will highlight the ﬁrst half of the
apparition. Tipped in our direction, this frozen CO2 button
will appear big and bright as it emerges from its winter hood
of clouds in late April and May. Watch it gradually shrink and
rift as opposition approaches. We'll also see part of the north
polar hood (NPH), a dull, diffuse cap of clouds shrouding the
north polar cap (NPC). Look for it along the planet's northern limb throughout the summer and early fall. The NPH is
often confused with the much brighter, more distinct true
cap, but that won't be visible until mid-winter 2019.
Spring in Mars's southern hemisphere occurs on May 22nd
with the cap at maximum extent. North of the SPC, keep a
180°

270°

225°

315°

Albedo Markings
Like the Moon, Mars readily reveals surface features called
albedo markings across its orange globe. Some change shape
with the seasons or from apparition to apparition depending
0°

45°

90°

135°

180°

-60°

+60°
+90°
180°

200°

Hyblaeus
Extension

220°

Protonilus

260°

280°

300°

320°

Ismenius Lacus

UTOPIA

240°

Solis
Lacus
MARGARIAURORAE
TIFER
Tithonius
SINUS
SINUS
Lacus
Phoenicis
Juventae Noctis Lacus
Lacus
Fons
Oxia
Achillis
Palus CHRYSE
T
HARSIS
Fons
NILIACUS
LACUS

Nodus
Alcyonius

Claritas

340°

0°

MARE
ACIDALIUM

20°

Idaeus
Fons

ARCADIA

E SI

REN

-40°
UM

-20°

AMAZONIS
Nix Olympica
(Olympus Mons)

40°

M A R E
60°

B O R E U M
80°

100°

120°

140°

160°

180°

p PRACTICE MAKES PERFECT The more often you observe Mars, the easier you'll find it to detect albedo markings. Use this map to identify them.
Damian Peach assembled this map from images he took during 2009-2010. The globes, tipped correctly for the current apparition, are from the software program WinJupos. Each globe displays the central meridian longitude that is directly below it on the map. Moderate telescopes will show only
the darkest, largest regions. South is up.

J U LY 2 0 1 8 * S K Y & T E L E S C O P E

0°

+20°
+40°

+40°
Propontis

R
R

ELYSIUM

Osiridis Pr.
Trivium
Charontis

Sigeus
Portus

+20°

Gomer
Sinus

Cerberus I

MAJO

sp
RR
IAPYGIA
e
HE
NUM
Tri ria
t
Si on
nu is
LIBYA
s
SYRTIS

0°

Deucalionis Regio
SINUS
US
SABAEUS MERIDIANI

S IN

MA R

TIS
M MARE ERYTHRAEUM
PEN
AE FRETU
PANDOR

SER
ARE

ELLAS

MARE CIMMERIUM

-20°

H
A
I A RE
TI
CU
M

M
DR

-40°

umasia

+60°
+90°

Sky and Telescope - July 2018

Table of Contents for the Digital Edition of Sky and Telescope - July 2018