58 AUSTRALIAN SKY & TELESCOPE APRIL 2016
ALAN MACROBERTM
arshasareputationof
being one of the biggest
disappointments through
a telescope. It spends most of its
time far from Earth, and it’s a
small planet to begin with. So it’s
usually just a tiny, shimmering
fuzzball. Mars passes close to
us only every 2.1 years around
its oppositions, and even then it
comes and goes fairly quickly.
Moreover, because Mars has a
rather elliptical orbit, many of its
oppositions are relatively distant.
But now everything is coming
together better than it has in 10 years.
We’re currently on the upswing
of Mars’ 16-year cycle of oppositions
near and far. By April 1, its globe
seen through a telescope will
reach an apparent diameter of 11. 9
arcseconds, enough to show surface
features fairly well through a sharp
1 0- or 15-cm telescope during
excellent seeing. By May 1, Marswill be 16.1′′wide,andwhenittops
out for the week around May 3 0, its
closest-approach date, it will appear- 6 ′′across. Seen through a 200 ×
eyepiece,that’slikeaping-pong2.2
metres away. Not bad.
Opposition comes eight days
earlier, on the 22nd, when Mars
willshineatanalmostJupiter-like
magnitude–2.1.Marswillremain
larger than 14 ′′all the way from
April 17 to July 21.
And the good news for southern
observers is that, this season,
Mars will be fairly far south, in or
near the head of Scorpius around
declination –21°, so it will be nice
and high for those of us in the
southern temperate latitudes.
As always, give your telescope
plenty of time to cool to the
surrounding air temperature before
expecting good views at high power.
Observe often to catch nights of
fine seeing. And spend lots of time
watching for everything on Mars
that is possible to glimpse; more
comes out with time.
Here are some things to look for.The polar caps
We’ll see Mars nearly equator-on
this season, with its north pole
tilted only slightly into our view
and the south pole tilted slightly
away. The planet’s northern
hemisphere is currently in the
height of its long summer (which
runs from January 3 to July 5 this
year), so in April and May the
North Polar Cap should already
be very small and continuing to
shrink. The Martian southern
hemisphere is having winter, so the
edge of the South Polar Hood of
winter clouds may peek into view
around the planet’s southern limb.
The southern cloud hood should
be larger but probably less brilliant
white than the North Polar Cap.NASA/JPL-CALTECH/MSSSRed Planet
April’s Mars
Mars moves into its best showing in a decade.