How to View Mars
Mars rising over the desert at dusk
near an opposition.
Contents
Introduction
If you like lunar and planetary
astronomy, you’ll probably love trying to spot surface features on Mars
– the only planet for which that’s possible (the rest are just
clouds). It’s something I’ve been trying to do since I was about
nine.
But it’s just not as easy as it
sounds (which is part of the fun). Why?
Mars’ visible features are
mostly low-contrast differences in surface colour and brightness (albedo), or
relatively small features (ice caps and clouds). Then there’s the problem
that Mars isn’t around all that often…
Mars Oppositions
Mars only comes observably close to
Earth for a few months every two years (about every 780 Earth days), when it is
at ‘opposition’, i.e. when it is positioned on the opposite side of
Earth from the Sun and so closer. This is because Earth completes an orbit in
less time than Mars – in accordance with Kepler’s laws - and so it
‘overtakes’ Mars on the inside at 780 day intervals.
These oppositions change over longer
cycles, making some more favourable than others, because Mars has a slightly
elliptical orbit. How close it gets to Earth depends on whether Mars is at
perihelion or aphelion - the nearest or furthest nodes in its orbit – at
opposition.
Mars’ orbital plane is also
slightly tilted with respect to Earth’s, overlaying yet a third level of
cyclicity to its regular comings and goings. So how big Mars appears in the
eyepiece and how high it gets in the sky – even close to opposition
– varies. A lot.
Before space probes started to arrive
at Mars in the 1960s, this cycle of oppositions ruled professional research on
the red planet. For amateurs it still does.
What does all this mean to you? If
you want to view the Red Planet, you’ll have short windows of opportunity
and those opportunities will vary.
Here’s a table of the next five
oppositions, with Mars’ maximum angular size and the approximate altitude
it transits (when it crosses the N-S meridian and is at maximum altitude in the
sky, so best for observing) at opposition for northern Europe.
(For comparison, the best opposition
in all our lifetimes happened on August 28th 2003 with an apparent
size of 25.1” – almost twice it’s
maximum in 2027!)
As you can see, the 2025 opposition is
the most favourable for many years to come: small but at a very observable
altitude.
|
Year |
Date |
Max size |
Transit Altitude Europe |
|
2022 |
8th December |
17.1” |
~60° |
|
2025 |
16th January |
14.6” |
~60° |
|
2027 |
19th February |
13.8” |
~51° |
|
2029 |
25th March |
14.4” |
~37° |
|
2031 |
4th May |
16.8” |
~20° |
Telescopes for Mars
Do you need a special telescope to
view Mars? In a word, no. But Mars - small, low-contrast and red - demands a
lot from a scope.
Some guidelines:
· Aperture matters less than you think:
a small telescope will resolve as much as the seeing allows most nights
o
Even
a fine 3” refractor will give good views near opposition (see example
below), but…
o
~~4”
is the minimum for detailed views in a refractor, 5” in a Maksutov,
6” for a reflector
· Optical quality is very important
– poor optics usually just show a fuzzy orange ball. Optical quality is
probably even more important in reflectors
· Reflectors and catadioptrics with
smaller central obstructions work better in all but the best seeing
· Doublet refractors are best at F7 or
over: faster doublets are often optimised for imaging and so compromised in the
red, giving a significantly less sharp view of Mars
· Critical focus is vital. If your
focuser isn’t great, consider an eyepiece micro-focuser – an
accessory that slots into your diagonal
· Collimation needs to be spot-on
(usually more of a factor for reflectors)
For locations with average seeing,
I’d narrow the choice to one of the following:
· Refractor: 4 – 6” aperture:
o
Achromat
- F10+
o
Doublet
apochromat - F7+
o
Triplet
apochromat – F6+
· Newtonian reflector: 5 –
10” aperture, F8 with an obstruction of ~25% and good optical quality
· Cassegrain or Maksutov: 4 –
8” aperture, F10+ with an obstruction of ~33% or less
If you’re viewing from
somewhere with really stable seeing, then a larger aperture will show more and
other telescope types will likely work just as well (e.g. 12-16” Schmidt
Cassegrains with 35-37% obstructions).
I take a deeper dive into telescopes
for planets here.
These are just guidelines – get
out and view with whatever you’ve got. I’ve seen Mars’
classic standout feature – the arrow-head (or sometimes bikini) of Syrtis
Major – with a 50mm achromat!
This classic 80mm fluorite apochromat
on a tracking equatorial mount gives good views of Mars for a small scope.
For ED doublet refractors, longer
focal ratios are best, like this 100mm F9 Skywatcher ED Pro.
Only the best corrected triplets work
well on Mars at F6 and below: this F6 William Optics FLT-123 gives outstanding
views of Mars.
Newtonians with small secondaries,
like this 200mm F8, work well for Mars (this one gave my best ever view of Mars
with an amateur scope – at the 2003 opposition).
Orion Optics’ excellent
planetary Maksutov – the OMC140.
A stable focuser with an inner
micro-focus wheel is ideal.
Eyepieces for Mars
Eyepieces matter less than many think
- less than the telescope itself, less than the mount and much less than the
seeing. But again, some factors to consider:
· You’ll need relatively high
magnification (100x or more, even when Mars is at its largest), so eyepiece
focal lengths:
o
2.5mm
– 6mm for small refractors
o
10mm-20mm
for small to medium SCTs and Maks and Newtonians
· For telescopes with driven mounts, a
high-quality simple eyepiece like an Orthoscopic is best. Field of view matters
less than eye relief (for comfort, but also to avoid getting it greasy or
steamed-up from your eye whilst viewing)
· If you’re using a manual push-pull
mount like a Dobsonian, an eyepiece with a big flat field
is best, because otherwise the vibes will only just have settled before
it’s time to move the scope again!
· Eyepiece comfort is underrated for
seeing fine detail: the tiny eyelenses and zero eye
relief of short focal length Plössls and basic Orthos
don’t help
· Most important – keep the eye
lens clean. Baader’s Optical Wonder cleaning fluid works for me
Again, I’ve taken a deeper dive
on eyepieces for planets here.
Zeiss’ Abbe Orthoscopics are
well-regarded (if rare and expensive) planetary eyepieces.
Takahashi’s MC Orthos are another traditional choice, since replaced by
their own Abbe Orthos – cheaper than
Zeiss’!
For scopes on push-pull mounts like
Dobs, eyepieces with wide fields work best: Tele Vue’s Ethos range are
surprisingly good for planets.
Mounts for Mars
A solid, stable, preferably tracking
mount is an under-rated factor for viewing at high magnification. Keeping Mars
steady in the field of view for minutes at a time really helps you to relax,
enjoy the view and see those low-contrast features.
For alt-azimuth mounts, I prefer one
with slow-motion controls rather than simple push-pull for high magnifications
(see below).
A stable tripod can really make a
difference to the same mount. The APZ below is much more stable with a heavier
tripod intended for larger Vixen mounts than the one it came with.
In my experience, it’s
remarkable how much better the same scope seems when it is tracking and
vibe-free.
Alta-azimuth mounts work best for
high magnifications if they have slo-mo controls,
like this Vixen APZ.
Tracking equatorial mounts are best for
high powers. Scope is another planetary ‘classic’ – Takahashi’s
FC-100 with an MC Ortho eyepiece.
A mini planetary setup you can grab
and go with: Takahashi’s FOA-60 on PM-SP driven mount.
Location and Seeing
Good seeing is the most vital factor
for high power viewing and especially for those low contrast albedo markings on
Mars. Fine seeing makes a mediocre scope seem great; bad seeing a fine one
mediocre.
Dark skies aren’t important,
but a lot of ambient light can be distracting. If Mars looks like a mushy ball,
don’t give up, it’s probably not your scope. Keep trying until you
get a night of good seeing.
If travel is an option, consider
desert areas with dry and stable air and higher altitudes. Lay-bys and car
parks off roads leading to observatories are a good place to start –
pro’s choose their locations carefully for good seeing. The desert
location for the first photo is a lay-by off the ET Highway in Nevada.
Seeing matters most - almost any
scope gives great views from Mauna Kea with an average of 0.45”.
Imaging Mars
I’m not an expert planetary
imager, but the requirements for imaging Mars are a bit different from viewing.
Contrast delivery by the scope is less important because the stacking process
automatically increases contrast. The same is partly true of seeing,
because stacking helps eliminate the blur caused by atmospheric turbulence.
Meanwhile, any false colour fringing is really noticeable in stacked images.
To get the best image you’ll
want a large image scale on your chip, so smaller refractors that might give
you a good view aren’t ideal for imaging Mars. If you want to try imaging
with a smaller refractor you will need a barlow lens
to multiply the effective focal length (and so image scale).
Ideally, you need a
longer-focal-length telescope (maybe a Maksutov or SCT) with accurate tracking
to keep the image on the (small) chip of the camera, whether a specialist
planetary CCD, a consumer camera in video mode or an old webcam. Then
you’ll need stacking software to process the video stream frame by frame
and combine the best.
Fantastic results can be had by the
patient and skilled. For what’s possible, check out Damian Peach’s
images online.
A Mars Challenge
I’ve always wanted to see Nix
Olympica, the Snows of Olympus - the name given to the bright cloud cap that
sometimes cover Olympus Mons, the highest (known) volcano in the Solar System. So
far, I never definitively have done, but it’s a fun challenge to sustain
those chilly Martian vigils at the eyepiece!
Viewing Mars with one of my favourite
telescopes – Takahashi’s FS-128.
Viewing Mars with at opposition in
2022: Takahashi FSQ-85 gave surprisingly good views!