Observe
MARS
at its best
It’s been 15 years since the Red Planet was this close and this big. Set up
your scope, and take advantage of this apparition. by Michael E. Bakich
Although a bit
farther and smaller
than it appeared
in 2003, Mars in
2018 will appear
much larger than
during its worst
opposition, more
than 800 years
from now. ASTRONOMY:
PLANETARY OBSERVING HITS A HIGH
point this summer as Mars once again dominates
the evening sky. Dust off your scope, because this is
the year to observe the Red Planet. It hasn’t been this
big and bright since 2003, and it won’t be again until
September 2035.
So, excitement is building. For readers new to Red
Planet mania, astronomers’ interest peaks during times
ROEN KELLY
Middle ground
63,070,000 miles
Sun
35,785,000 miles
34,580,000
miles
Earth
August 2003
58
A ST R O N O M Y • MAY 2018
July 2018
March 2832
called oppositions, when Mars lies opposite the Sun from
our perspective on Earth. This year’s opposition occurs
July 26 or 27, depending on where you live. Let me
explain.
Dates and numbers
The moment of opposition occurs at 5h13m Universal
Time on the 27th. In the United States, that’s 1:13 a.m.
EDT. If you observe from the Mountain or Pacific time
zones, the date of opposition will be the 26th.
Then, a scant four days later, Mars reaches its closest
point to Earth. An opposition happens every 780 days
(minus 1 hour 26 minutes 24 seconds, to be exact). But
each closest approach to Earth is not really, well, closest
because Earth’s and Mars’ orbits are not circular, so the
distance between our two worlds changes from one oppo-
sition to the next.
During a distant opposition, Mars can lie more than
60 million miles (97 million kilometers) away. Contrast
that with a nearby opposition that places Mars less than
35 million miles (56 million km) from Earth.
For observing purposes, it all comes down to apparent
diameter. Astronomers use angular measurement to
describe how large a celestial object appears. A planet’s
angular size can change a lot. Mars varies in size at oppo-
sition from a minimum of 13.8" to a maximum of 25.1".
And its maximum brightness at each close approach var-
ies from magnitude –1.5 to –3.0.
In 2018, opposition occurs July 27, but Mars lies closest