How to View Mars
Mars rising 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.
As you can see, for Europe, the 2022
opposition is the most favourable for many years to come.
|
Year |
Date |
Max size |
Transit Altitude EU |
|
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 the maximum the seeing will allow on 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 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 choose one of the following:
· Refractor: 4 – 6” aperture:
o
Achromat
- F10+
o
Doublet
apochromat - F7+
o
Triplet
apochromat – F6+
· Newtonian reflector: 6 – 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
(at least 80-100x up to 200x 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.
A Mars-worthy Mount
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).
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.