Australian Sky & Telescope - June 2018

and Sinus Meridiani (east of Syrtis Major); the great bands

of Mare Tyrrhenum and Mare Cimmerium that stretch west

ofSyrtisMajor;thevastandamoebicMareErythraeum-

Aurorae Sinus complex; and the dark eye of Solis Lacus. In the

northern hemisphere you can’t miss the dark thumb of Mare

Acidalium and Niliacus Lacus located at the same longitudes

as Mare Erythraeum.

But identifying albedo markings can take time. Most are

subtleanddifficulttopickoutagainsttheglaringorange

landscape;butwithpractice,theybecomeeasiertoseeuntil

yourecognisethemlikecontinentsonaglobe.Tomakethe

taskeasier,observetheplanetwithasmuchmagnification

allowedbytheseeingconditions.I’vealwaysfoundared

#23Afilterabighelpinboostingtheircontrast.

This is especially true when viewing Mars’ ‘boring’

hemisphere, located between about longitudes 110° and

240°, which includes the narrow polar-hugging stripe of

MareSirenumandthelow-contrastvolcanoesoftheTharsis

Plateau.OrographiccloudsoftencoverOlympusMons,the

planet’slargestextinctvolcano,makingitlooklikeapale,

whitepustuleintheochredesert.

Clouds, hazes and dust storms

OneofthemostexcitingaspectsofobservingMarsis

discoveringitssimilaritiestoEarth.Bothplanetshavetheir

shareofclouds,fogandmist.OnMars,theseoftenappear

as narrow bands of white haze along either the morning

oreveninglimbwheretheSunisjustrisingorsetting.In

SHARPEST VIEW

These images captured

during the planet’s 2012

apparition show many

ofMars’darkalbedo

markings. The planet

rotates every 24 hours, 38

minutes.Sincethat’svery

similartoEarth’srotation,

we view nearly the same

hemisphere from night to

night. If you observe Mars

at 11 p.m. from the same

place night after night, the

planet will appear to rotate

in retrograde (backward)

overaperiodofaboutsix

weeks. If you see Syrtis

Major front and centre

at11p.m.theirstnight,

youwillseeitinthatsame

spotaboutsixweekslater.

Toseeadifferentsideof

the planet, you need to

observeMarsatadifferent

timeofnightorfroma

differentlongitude.South

is up.

SYELLOW STORM RISING With frequent observing, you can detect

changes in the day-to-day appearance of Mars. For example, a dust

storm erupted on the planet in October 2005. By recording images

each night, Sean Walker was able to track the progress of the yellowish

clouds as they travelled across the planet’s dark surface. South is up.

my experience, these are the most common clouds visible

through amateur telescopes, but watch for isolated puffs

and high-altitude clouds that hug Martian volcanoes. A blue

#80A filter will enhance their visibility.

In the opposite hemisphere, autumn will be underway

during Earth’s winter and spring, with clouds forming over

the north polar cap (NPC) and beyond to create the NPH.

By October, the NPH may extend as far south as latitude

50° north, giving the ‘top’ of Mars a diffuse, off-white cast

as if it had been dipped in milk. Isolated clouds can appear

anytime, especially as the SPC shrinks through the summer

and fall.

One of the most dramatic events to witness is a dust storm

— as long as it doesn’t expand to become a planet-encircling

event! This last occurred in June 2007, when, within a few

Sinus

Sabaeus

Mare

Cimmerium

Mare

Tyrrhenum

Hellas

Syrtis

Major

Utopia

Margaritifer

Sinus

Mare

Sirenum

Olympus

Mons

Mare

Erythraeum

Aurorae

Sinus

Chryse

Niliacus

Lacus

Mare

Acidalium

Sinus

Meridiani

Limb

haze

North

Polar Cap

Olympus

Mons

Evening

clouds Hyblaeus

40 AUSTRALIAN SKY & TELESCOPE July 2018

MARS OPPOSITION