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A Guide to Observing

Mars in April 2014

A Guide by One-Minute Astronomer

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Table of Contents

Overview of This Guide ................................................................................ 4

An Overview of the Planet Mars ................................................................. 6

Insight and Blunder: Past Observations of Mars .................................... 10

The Martian Surface .................................................................................. 12

Oppositions of Mars .................................................................................... 14

Observing Mars in a Telescope ................................................................. 18

What to Look for on Mars in a Small Telescope ..................................... 24

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Overview of This Guide

Mars reaches opposition on April 8, 2014 and makes its closest approach

to Earth a few days later. This will be the best time in the last six years to

see the Red Planet, and the window for optimum observing will last just a

month or so. So it’s time to have a look at what to expect and some tips

on how to observe this small but fascinating world.

Mars at it appears in a small telescope

This guide will recount for you the history of Martian observation. It will

give you an overview of the planet itself, a planet which has a surface area

as large as the land area on Earth. And it will give you some tips on how

to observe the planet with a small telescope.

To find Mars in April 2014, look to the east an hour or two after sunset.

You can’t miss it… it is red-orange and brighter than any other star in the

sky. On April 8th, the planet rises as the Sun sets. That’s where the term

“opposition” comes from… the planet is directly opposite the Sun in the

sky. After the 8th, the planet will rise a little earlier each night. The image

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below gives you an idea of where Mars is located in mid-month. The plan-

et is easily seen with the unaided eye or with binoculars any time after it

rises. But it’s best observed with a telescope when it rises higher in the

sky well after midnight.

Mars at it appears on April 11 at 10 p.m. local time in mid-northern latitudes. The planet

lies above and outshines the bright white star Spica

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An Overview of the Planet Mars

As one of the five bright planets visible to the unaided eye, Mars has per-

plexed and tantalized stargazers since antiquity. Its ochre-red color, a

consequence of iron-oxide in its surface sands, prompted classical astron-

omers to name the planet after the Roman god of war. Mars moves rela-

tively quick across the sky compared to the other superior planets Jupiter,

Saturn, Uranus, and Neptune. At an average distance from the Sun of

about 1.52 astronomical units (AU), Mars moves in a complete orbit in 687

days (about 1.88 Earth years).

The four terrestrial planets to scale: from left to right, Mercury, Venus, Earth, and Mars

Mars is the outermost of the four terrestrial planets. Among the eight ma-

jor planets of our solar system, only Mercury is smaller. Mars has a radius

at the equator of about 3,400 km, about 53% that of Earth. This gives is

a surface area about 28% that of Earth, which is about the same area

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covered by Earth’s landmasses. The planet has some 15% if Earth’s vol-

ume and just 11% if its mass, so it is a little less dense. Mercury has a

higher density than Mars and a smaller radius, so its surface gravity is

about the same as Mars, that is, about 37.6% the surface gravity of Earth.

Whereas Mercury has no atmosphere and a Moon-like surface, and Venus

is shrouded in dense poisonous clouds, Mars has a surface far more similar

to Earth. It does have ancient craters and plains like our Moon, but it also

features gigantic shield volcanoes far larger than any on Earth, windswept

deserts, polar ice caps made of frozen carbon dioxide and water, and a

thin atmosphere of carbon dioxide.

Like Earth, Mars has a dense molten core of iron and nickel, a silicate

mantle, and a thin rocky crust. The crust is thicker on average than

Earth’s, and the mantle does not support plate tectonics. While there was

obvious volcanic activity on Mars billions of years ago, such activity has

largely subsided.

Mars currently has no global magnetic field or magnetosphere, so it is

peppered directly with solar radiation. The ancient rocks on the surface of

Mars have been magnetized however, so it’s likely the planet had a mag-

netic field in its early days. Surface rocks on the planet, as on Earth, con-

tain silicon, oxygen, and traces of metals. Much of the rock appears to be

volcanic in nature. The reddish color of the planet is a consequence of

surface dust rich in iron oxide (rust).

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As William Herschel noted, Mars’ rotational axis is tilted by 25.4o, so the

planet has seasons, and the polar caps grow and shrink with the seasons.

Most of the caps consist of a layer of carbon dioxide frozen out of the at-

mosphere. The northern polar cap is just 1m thick, while the southern po-

lar cap is about 8 m thick. Underneath this each layer is a base of water

ice about 2 km to 3 km thick. Each cap is in total darkness for about half

the year. When summer brings sunlight to a cap, it sublimates carbon di-

oxide and some water into the atmosphere at a rapid rate, leading to

strong winds and dust storms that flow from the poles to lower latitudes.

A view of the Martian atmosphere from orbit

Like Venus and Earth, Mars has an atmosphere. It’s thin, with about the

same average pressure as Earth’s atmosphere at an altitude of about

110,000 feet, or about 0.6% the average pressure of Earth’s atmosphere

at sea level. Because of this low pressure, liquid water cannot exist on the

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planet for any length of time. Mars’ atmosphere is some 96% carbon di-

oxide, with large traces of argon and nitrogen, and lesser traces of oxygen

and water. Clouds of ice form in the atmosphere occasionally, and wind-

storms sometimes kick up locally, or, on occasion, globally such that the

entire planet is shrouded in dust. Such storms seem to occur when the

planet is closest to the Sun. Even during periods of calm, the atmosphere

is rich in fine dust which gives it an orange-pink color from the surface.

From Earth, it appears the entire planet is wrapped in a faint bluish haze.

The scant atmosphere retains little heat and Mars gets less than half the

sunlight as Earth, so the planet is colder than Earth. Its surface tempera-

tures range from -140oC at the poles to a surprisingly warm 35oC near

equator at perihelion.

Valles Marineris seen from Martian orbit

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Insight and Blunder: Past Observations of Mars

In the 19th century, the Italian astronomer Giovanni Schiaparelli reported

detailed views of the planet’s surface including an apparent network of

channels, or canali, in Italian. These channels appear to be connected by

tiny dots, although both seemed to flash in and out of view during mo-

ments of steady seeing. Schiaparelli and many of his contemporaries sus-

pected these features were illusory and hoped that better telescopes

would reveal the true nature of the features on the surface of Mars.

A drawing by Percival Lowell of the Martian “canali”

In the late 19th century, the wealthy and imaginative amateur astronomer

Pervical Lowell built a research-grade observatory in Flagstaff, Arizona, to

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study the planet. Lowell Observatory remains there to this day. His optics

were far better than Schiaparelli’s, and he was no doubt aware of the pos-

sibility the canali were illusions. Yet Lowell claimed to not only see the ca-

nals clearly, he proposed they were evidence of advanced civilization on

the planet. He wrote prodigiously about the subject for popular audiences,

which often set him at odds with professional astronomers of the day,

none of whom could verify his observations.

The possibility of life on Mars remained in the popular imagination until

1965 when the Mariner 4 spacecraft flew within 10,000 km of Mars and

imaged craters on the Martian surface. This was bad news for the pro-

spects of life: craters meant thin atmosphere and little erosion from wind

or surface water. The story got more interesting in 1971 when Mariner 9

orbited the planet and captured thousand of images of craters, yes, but

also massive volcanoes and what appeared to be dry riverbeds and flood

zones, and canyons, one of which was a long as the continental United

States. There were no canals: these turned out to be optical illusions that

plagued Earthbound telescopic observers.

From 1976 onward, starting with the American Viking landers, planetary

scientists have dispatched an array of high-tech orbiter, landers, and rov-

ers to search for evidence of water, methane, and other atmospheric gas-

es and soil components that might give some evidence of life on the plan-

et. None have resulted in any indication of life on Mars, but the geology,

geography, and chemistry of the planet have become much better under-

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stood. The planet appears in many images to be remarkably Earth-like,

looking much like a rocky desert landscape on Earth, with occasional evi-

dence of winds, frosts, dust storms, and large quantities of frozen water in

the polar caps. Much of this water presumably flowed on the surface long

ago, creating many of the now dry rivers and canyons we still see. Be-

cause Mars is so cold and its atmospheric pressure so low, the water no

longer flows and remains trapped in the polar caps and possibly under-

ground.

An image of Utopia Planita on Mars captured by the Viking 2 lander

The Martian Surface

The surface of Mars is classified into two types of regions, the lighter red-

orange regions covered with rusty dust and the darker regions which are

large areas of exposed volcanic rock. During early days of telescopic ob-

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servation, the light regions were thought to be continents so they were

given names that described land masses. Major regions of this type in-

clude Elysium Planitia (the Elysium Plain), Arabia Terra (Land of Arabia),

the circular Hellas Planitia (Plains of Greece), and Amazonis Planitia (Ama-

zon Plains).

The darker regions were names after seas, lakes or other watery features.

So there is the very large Mare Erythraeum (Arabian Sea) in the south,

Mare Acidalium (named after a legendary fountain) in the north, and most

strikingly, the large wedge-shaped feature Syrtis Major named after the

Gulf of Sidra off the coast of Libya. Syrtis Major is the most obvious dark

region on the Martian surface. Many of these dark regions appeared to

early telescopic observers to change size during the Martian year. They

suspected this was caused by changes in vegetation or rainfall. It turns

out the dark regions do not change their dimensions, but instead occa-

sionally are obscured by atmospheric dust. Schiaparelli and especially

Lowell noted the region called Solis Lacus (Lake of the Sun), just south of

what we now know to be Valles Marineris, seemed to wax and wane with

the seasons. Lowell observed many (illusory) canals converging in this re-

gion and speculated it was the capital of the Martian civilization. Solis La-

cus is a part of what’s now called Solis Planum. Observers often remark

that these dark regions appear green. They are not… they are grey-brown

and simply appear green because of the contrast with the red-orange sur-

roundings.

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In some images of Mars from space or from Earth-based telescopes, whit-

ish features are visible. These are usually cloud formations. They are as-

sociated with low-lying regions where clouds collect, or in the vicinity of

the peaks of volcanoes where warm air rises up the side of the mountain

and condenses into clouds.

Clouds near the peaks of Olympus Mons (upper left) and the three volcanoes that make

up Tharsis Montes

Oppositions of Mars

Like all superior planets, Mars is best observed when it is near opposition,

that is, opposite the Sun in the sky as seen from Earth. That’s when the

planet is nearest to Earth and therefore easiest to observe. The period in

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the weeks before, during, and after opposition of Mars is often called an

apparition.

The slower moving outer planets Saturn, Uranus, and Neptune arrive at

opposition every year plus a few days or weeks. That’s because Earth

moves around the Sun much faster than these distant worlds. Even Jupi-

ter moves just about 1/12 of the way around the Sun before Earth catches

up to it again. So the oppositions of Jupiter are about 13 months apart.

Earth, the Sun, and a superior planet at opposition

With Mars, it is a little more complicated. Mars moves quickly around the

Sun, making a full orbit in just 1.88 years (687 days) while Earth moves

even faster on its inside track closer to the Sun. The upshot is that it

takes, on average, about 780 days (about two years and two months) for

the faster-moving Earth to catch up to Mars such that it is at opposition.

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Ellipticity of the Martian orbit (shown here in red) means a large variation in the Earth-

Mars distance at opposition

But not all Martian oppositions are alike. Because the orbit of Mars is sub-

stantially elliptical, there is a large variation in the distance from the Earth

to Mars at opposition. If opposition occurs when Mars is closest to the

Sun, the two planets can get as close as 35 million miles (56 million kilo-

meters) and the planet grows to a respectable 25” in apparent diameter

and a magnitude of -2.8. When opposition occurs at aphelion, Mars gets

to within just 60 million miles (100 million kilometers) and subtends an an-

gle of just 15”. Jupiter at opposition, by comparison, grows to about 50”

in apparent diameter.

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Every 15 or 17 years, Mars reaches opposition within a few weeks of peri-

helion, which gives a particularly good apparition. The opposition in 2014

is not particularly favorable, but it is better than the last two in 2010 and

2012.

Variation in relative apparent size of Mars during oppositions from 1995-2005 (credit:

NASA)

The closest approach in 60,000 years occurred in August 2003 when Mars

came within 55,758,006 km. Since then, Mars and Earth have been get-

ting farther apart at opposition, though the situation is slowly improving.

A table showing details for the next few oppositions is below.

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Opposition Date Distance (km) Apparent Size Constellation

April 8, 2014 92.8 million 15.1” Virgo

May 22, 2016 76.1 million 18.4” Scorpius

July 27, 2018 57.7 million 24.1” Capricorn

October 13, 2020 62.6 million 22.3” Pisces

December 8, 2022 82.2 million 16.9” Taurus

As Mars nears opposition it begins a period of retrograde motion which

lasts a little more than two months. During this time, it appears to move

backwards (westward) in a looping motion relative to the background stars

before slowing down, stopping, and moving eastward again.

At conjunction, Mars can be some 400 million kilometers away and can

shrink to a tiny, almost featureless disk just 3” or 4” across.

Observing Mars in a Telescope

While Mars seems to be continually swarmed and monitored by cutting-

edge space hardware, it’s still a splendid target for a small telescope. This

ochre world is notoriously small and hard to observe visually, but it re-

wards the patient stargazer with sights unseen elsewhere in the solar sys-

tem. In steady sky at high magnification, you get glimpses of a constantly

changing planet, with evidence of atmospheric cloud, fogs, dust, dark re-

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gions rock and craters, red deserts, and of course the polar caps which

grow and shrink with the seasons. Beginners are often disappointed with

their first look at Mars in a telescope. But as your expertise grows, you

will learn to see an astonishing amount of detail on the Red Planet when it

approaches opposition.

A full-planet map of the Martian surface. If you are online, click on the link below to open

a high-resolution version of this map in a browser window.

http://oneminuteastronomer.com/wp-content/uploads/2013/02/Mars-map-mid.jpg

During an apparition, Mars grows in brightness to magnitude -1.4 to -2.8.

For the 2014 opposition, it will reach magnitude -1.5, a little brighter than

the brightest star Sirius, and a modest apparent diameter of about 15”.

Maximum size and brightness occurs in during the several days after April

http://oneminuteastronomer.com/wp-content/uploads/2013/02/Mars-map-mid.jpg

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8, 2014. It will shrink slightly and grow fainter after this time, but it will

still make for good viewing during all of April 2014.

The color of the planet will be lovely to the unaided eye and especially so

in binoculars. But to see any detail on the surface, you will need a tele-

scope.

Of course, the best telescope to use is the one you already have. Longer-

focal lengths give you higher magnification and bigger images with a given

eyepiece, so if you have a short-focal-length scope you will want to use

shorter focal-length eyepieces or a Barlow lens to get higher magnifica-

tions. Refractors, which have no central obstructions, tend to give better

contrast. But larger aperture reflectors can give better resolution of fine

detail because of their larger apertures. You will want to use a magnifica-

tion of at least 150x to get a decent view of Mars. This magnification will

make the planet look just a little larger than the full Moon appears to your

unaided eye. Work your way higher if your equipment and seeing condi-

tions allow, up to a maximum magnification of 50x-60x the aperture of

your scope (in inches).

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Mars in a telescope at 100x on a night of steady seeing

As for eyepieces, again, use what you have. The best eyepieces for ob-

serving planets have simple designs with few optical elements and a mod-

erate field of view. You don’t need $400+ eyepieces for planets. A good-

quality Plossl or Orthoscopic eyepiece will do just fine.

Some other observing tips:

• Acclimatize Your Telescope. Bring your scope out at least 30-60 minutes

before you plan to observe. By cooling it down to the ambient tempera-

ture, you’ll prevent air currents inside your scope from degrading the im-

age of the planet.

• Pick a Night With Steady Air. Seeing is critical when observing Mars. So

pick a night when the air is steady and the stars aren’t twinkling too much.

Vigorously twinkling stars mean poor seeing, even if the sky is clear.

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Sometimes, nights with a little haze have steadier air than crystal-clear

nights.

• Observe Frequently. Because Mars rotates every 24 hours and 37

minutes, you’ll see almost the same face of the planet at the same time

each night. So extend your sessions over several hours on one night, or at

the same time over the course of the next month to see both sides of the

planet.

A #21 Wratten filter threaded for a 1.25” eyepiece: an essential filter for observing Mars

To get better contrast of the planet’s surface, try a few colored filters if

you have them. Here are some suggested filters for Mars observing ses-

sions. Recall you learned a little about colored filters in Month 10:

• Orange (#21 or #23A) increases contrast between light and dark fea-

tures and penetrates hazes and most clouds. If you pick just one filter for

observing Mars, get a #21.

• Yellow (#12, #15) can brighten desert regions and darkens bluish and

brownish features.

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• Red (#25, #29) gives maximum contrast of surface features, enhances

fine surface details, dust clouds boundaries, and polar cap boundaries.

• Green (#57) darkens red and blue features, enhances frost patches, sur-

face fogs, and polar projections

• Blue (#80A, #38, #38A) and deep blue (#46, #47) shows atmospheric

clouds, discrete white clouds, and limb hazes, equatorial cloud bands, po-

lar cloud hoods, and darkens reddish features

Also, you need to manage your expectations. No matter how big your

scope, Mars won’t look anything like images you see the magazines or

astro websites. In a small telescope, Mars looks tiny and gives up little de-

tail at a glance. Astronomy writer Timothy Ferris said of observing the

planet, “Observing Mars through a telescope is like watching the Dance of

the Seven Veils: seldom are you certain of exactly what you’ve seen, but

it’s enough to pique your interest”.

The most important tool for observing Mars is patience. You must look

with patience and wait for moments of good seeing when the air is steady

and tiny detail emerges. Even on a small disk, you can see an astonishing

amount of detail if you look carefully, on and off for long periods of time,

and wait for steady air.

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What to Look for on Mars in a Small Telescope

In a small telescope, only the largest geographical regions are visible on

the surface of Mars. You won’t see any craters, volcanoes, or even the

enormous Valles Marineris. If you are really fortunate, you might see a

small white dot that marks clouds above Olympus Mons, but this is an in-

frequent sight.

When you first starting observing Mars during an apparition, you must try

to find which major features are visible. Then, expect your view to change

slowly from night to night. Mars rotates in the same direction as Earth

every 24 hours and 37 minutes, just a little longer than it takes Earth. If

you observe Mars with a direct view with north up and east to the left, the

planet will will appear to move from left to right. If you view through a

diagonal with a SCT or refractor, the image will be flipped left-right. With

a Newtonian, the view will be inverted up-down and left-right.

If you observe Mars at the same time every night, features on the surface

will appear to move out of view 37 minutes earlier each night. The overall

effect makes it appear Mars makes a full backward revolution every 40

days. That’s backward in the sense that the planet appears to rotate in an

opposite sense from Earth.

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The image above from SkyandTelescope.com gives you a number of faces

of the planet as it rotates during a Martian day. In this image, south is up.

As you first look at the planet during an apparition, find out which features

you are looking at. Then, from hour to hour and night to night, you can

follow the motion of these features on the surface of the planet. In this

image, south is up. So if you are using optics that do not invert the im-

age, you must make mental accommodation for this map.

The key features to look for on Mars include:

• The arrow-shaped dark region of Syrtis Major (see above image at 270o)

• The southern dark features including Mare Tyrrhenum (at 225o), Mare

Erythraeum (at 45o), and Mare Sirenum; also look for the circular reddish-

orange feature Hellas (at 315o in the image above)

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• The broad ochre regions of rusty sand marked by Arabia and Eden Terra,

Tharsis and Arcadia, Amazonis, and Elysium, all of which are at equatorial

and temperate latitudes

• In the north of Mars, look for the dark areas of Utopia Planitia (at 270o)

and Mare Acidalium (at 45o)

• And of course look for the polar caps. At a glance, you will immediately

see which polar cap is most easily visible. In 2014, the north polar cap is

tilted towards Earth, and since it’s summer in the northern hemisphere of

Mars, the cap is small and slowly shrinking

And that’s about it. Looking at Mars, like looking at any object through a

telescope or learning to play the guitar or to windsurf, is a learned skill

that combines the mind, the body, and the imagination. It takes practice

and patience, so please don’t get frustrated and just keep at it!

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A Guide to Observing Mars in April 2014astronomer-wpengine.netdna-ssl.com/wp-content/... · A Guide to Observing Mars in April 2014 A Guide by One-Minute Astronomer ... discover and