Australian Sky & Telescope - June 2018

38 AUSTRALIAN SKY & TELESCOPE July 2018

Asalways,yourbeststrategyistoobservetheplanetas

often as possible to maximise the chance of getting a sharp

look during infrequent spells of excellent seeing, when all

drossfallsawayandtheplanetlooksasrealasbeingthere.

Remember to allow your telescope’s optics to cool to the

outside temperature, so they don’t become their own source

of‘boiling’air.Marswon’tbethisclosetoEarthagain

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 will remain in Capricornus for the next

fewmonths,makingabriefforaywestintoneighbouring

Sagittarius near the end of its retrograde loop in late August.

Minimum declination of –26° 33′willoccuronAugust15

andbytheendofOctoberstillbearespectable–17°.

What to see

Thesouthpolarcap(SPC)willhighlightthefirsthalfofthe

apparition. Tipped in our direction, this frozen CO 2 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

thenorthpolarcap(NPC).Lookforitalongtheplanet’s

northern limb throughout the winter and early spring. 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’ southern hemisphere occured on May

22 with the cap at maximum extent. North of the SPC,

keep a wary eye out for another polar cap look-alike, the

2,300-kilometre-wide impact basin Hellas. In June, Hellas

might be still be coated with frost or hidden under a blanket

of clouds, mimicking the appearance of a polar cap, but you

cantellthetwoapart—HellasisdistinctlynorthoftheSPC

and appears duller. Even small scopes should provide great

views of these polar features.

Albedo markings

Like the Moon, Mars readily reveals surface features called

albedo markingsacross its orange globe. Some change shape

with the seasons or from apparition to apparition depending

on how the Martian winds move bright surface dust around.

The most obvious southern hemisphere features include Syrtis

Major, an ancient shield volcano shaped like the subcontinent

India; the ‘chicken drumstick’ combination of Sinus Sabaeus

ARCADIA

UTOPIA MARE BOREUM

IAPYGIA

THARSIS

AMAZONIS

NILIACUS

LACUS

CHRYSE

AURORAE

SINUS

MARGARI-

TIFER

SINUS

SINUS

MERID-

IANI

Deucalionis Regio

Protonilus NILOKERAS

HELLAS MARE ERYTHRAEUM

ELYSIUM SYRTIS MAJORAERIA

ARABIAMOABEDEN

MARE

ACIDALIUM

SINU

SSABAEUS

MARE SERPENTISPANDORAE FRETUM

LIBYA

Hesperia

Tritonis

Sinus

Hyblaeus

Extension

Propontis

Tithonius

Lacus

Noctis

Lacus

Phoenicis

Juventae Lacus

Fons

Solis

Lacus

Claritas

Nix Olympica

(Olympus Mons)

Trivium

Charontis

Gomer

Sinus

Cerberus I

Idaeus

Fons

Achillis

Fons

Sigeus

Portus

Osiridis Pr.

HA

DR

IAT

ICUM

MA

M RE

AR

ET

YRR

HENU

M

Th

aumasia

0°

180° 200° 220° 240° 260° 280° 300° 320° 340° 0° 20° 40° 60° 80° 100° 120° 140° 160° 180°

180° 225° 270° 315° 0° 45° 90° 135° 180°

+20°

+40°

+60°

–20°

–40°

–60°

+90°

Oxia

Palus

Nodus

Alcyonius IsmeniusLacus

0°

+20°

–20°

–40°

–60°

+40°

+60°

+90°

MARE

SIREN

UM

MARE CIMMERIUM

SSOUTHERN ICE The south polar cap, which reaches 3 km deep in

places, is made up of frozen water and carbon dioxide.

SPRACTICE MAKES PERFECT The more often you observe Mars, the easier you’ll ind it to detect albedo markings. Use this map to identify

them. Damian Peach assembled this map from images he took during 2009–10. 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-aperture

telescopes will show only the darkest, largest regions. South is up.

MARS OPPOSITION