Australian Sky & Telescope - June 2018

http://www.skyandtelescope.com.au 41

diameter,itwascorrect.Multiply25′′× 75

and you get 31′,thefullMoon’sapparent

diameter.

Then an unfortunate thing happened. As the

email made the rounds, the reference to “at a

modest 75-power magnification” was left out,

leading neophyte skywatchers to expect

a frighteningly large, Moon-sized Mars

castingarustyspectreoverthelandscape.

Likeamosquitoyouhearbutforeverfail

to swat, the description has popped up at

everysubsequentopposition.Watchforit

to reappear on schedule this apparition, and

when friends ask what’s up, patiently explain

andthendirectthemtotherealthingright

outside their window.

Usethehypethatwillinevitablyspinoutofsocial

mediatoyouradvantagetoshareMarsandthejoysof

lookingupwiththosenewtothehobby.Anditwon’thurt

one bit if you mention how important minimising light

pollutionisforagreatdarkskyexperience.

„BOB KINGhas been an avid observer since childhood. He’s

a long-time member of the American Association of Variable

Star Observers (AAVSO) and author of multiple observing

guides, includingWonders of the Night Sky You Must See

Before You Die. Visit his blog atastrobob.areavoices.com.

USEFUL RESOURCES

Though the internet is often a tool for rumour-

mongering, it can also provide good information for

planetary observers. Here are a few sites to visit during

this opposition of Mars.

XSky & TelescopeMars

Profiler (https://is.gd/

marsprofiler)

XAssociation of Lunar and

Planetary Observers

(ALPO) Mars Section

(alpo-astronomy.org/

marsblog)

XThe Red Planet (https://

mars.nasa.gov/#red_

planet/)

XThe 2018 Perihelic

Opposition of Mars

(alpo-astronomy.org/

jbeish/2018_MARS.htm)

XHow to Make An

Occulting Bar (https://

is.gd/OccultingBar)

XMars Observers

Yahoo Group (groups.

yahoo.com/group/

marsobservers)

weeks, dust had blanketed nearly every feature

from view. Fortunately, such planet-wide

events are uncommon, with just 10 recorded

over the past 130 years.

The more often you observe Mars, the

more familiar you’ll be with any changes

in the appearance of albedo features that

mark the onset of a dust storm. Watch for a

familiar feature to disappear or a light area to

appear. Visually, dust storms appear as bright,

yellow patches. A #23A red filter will brighten and

enhance the view and serve to confirm that you’re

seeing dust and not water vapour clouds.

Dust storms are common during the

Martian southern summer, which begins

in mid-October. Good spots to keep an

eye on include the Chryse region and

Hellas-Noachis from late August through

November.

Phobos and Deimos

Close oppositions provide a perfect opportunity

to see the Martian moons, Deimos and Phobos.

Without the planet nearby, even a 75-mm telescope

would be up to the task: their 2018 opposition magnitudes

are 11.5 and 10.5, respectively. But Deimos strays just 1.2′

(arcminutes) and Phobos only 21′′ from the planet at best, so

you’ll need at least a 25-cm instrument and careful planning.

First and foremost, make your attempt around opposition

when the moons are brightest and their angular distance

from Mars is at maximum.

I saw both moons during the 2003 perihelic opposition

of Mars through a 28-cm Schmidt-Cassegrain telescope

by hiding the brilliant planet behind an occulting strip

made of aluminium foil taped across the field stop of an

ancient orthoscopic eyepiece. With Mars safely hidden

and a magnification of 233× applied, Deimos was an

obvious pinpoint of light in the glare. Phobos, though

brighter, orbits much closer to the planet and proved much

more challenging.

Go for it and surprise yourself. Several planetarium-style

software programs including the free Stellarium

(stellarium.org) display the moons, allowing you to

plan your observing session when either is at maximum

elongation from the planet.

Be a planetary ambassador

Finally, don’t forget to get the public involved. Who could

forget the internet rumor started in 2003 about Mars

appearing as big as the full Moon at opposition? I won’t

quote the full e-mail that bounded from inbox to inbox,

but surprisingly, its content was mostly true, as it claimed

Mars through a 75× eyepiece would look as large as the full

Moon to the naked eye. Since the post referred to its apparent

WNIGHT WATCH The author drew two sketches of

Mars, two hours apart, as viewed with a 25-cm

telescope at 256× on August 4, 2003 UT. The

sketches show the planet’s rotation as well as

several of its most prominent features, including

the dark ‘inger’ of Syrtis Major and the south

polar cap. In the bottom view, a dark rift shows in

the cap. Such rifts appear as the cap shrinks.

12:05 a.m.

2:30 a.m.

SE

ALBEDO MARKINGS: DAMIAN PEACH; SKETCHES: BOB KING