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The Planet Venus and ProblemsIts

BY WILLIAM H. PICKERING

Professor of Astronomy, Harvard University

THIS planet, which is at times very

conspicuous in our evening skies,

is, after the Moon, the brightest

member of the solar system, and is fre-

quently visible in the daytime, if we

know just where to look for it. It

reaches its greatest evening brilliancy

once every year and a half, and is then

capable of casting a very distinct shadow

upon any whitened surface. Since it

revolves in an orbit between the Earth

and the Sun, it apparently never recedes

very far from the latter body, the maxi-

mum distance being about 45. This

fact, together with its great brilliancy,

will assist us in recognizing it, since

in the evening it never appears any-

where but in the west, and in the morn-

ing only in the east. Its evening ap-

pearance was known to the ancients by

the name of Hesperus, and its morn-ing appearance as Phosphorus, which

leads us to believe that before the birth

of exact astronomy it was supposed that

two distinct bodies were involved. This

same mistake has been made several

times in the past with regard to bril-

liant comets.

Venus presents phases like the Moon,

but they are not. visible to the naked

eye, although they may be inspected

under favorable circumstances with the

aid of a goon opera-glass. Although

it comes nearer to the Earth than any

other planet, yet but little is known of

its physical characteristics-less, in fact,

than of either Mercury, .Mars, Jupiter,

or Saturn. Indeed, we may say that but

four facts are really known with regard

to it. First, its diameter is but two

hundred miles less than that of the

Earth. Second, its mass is about four-

fifths as great. The weight of a body

upon its surface would therefore be flve-sixths of its weight here. This is of

importance, since it is one of the fun-

damental conditions affecting the exist-

ence of its oceans and atmosphcre.

Third, the surface presents a uniform

brightness or albedo of 0.76. That is

to say, it reflects three-quarters of all

the light which falls upon it. White

paper reflects seventy-eight per cent.,

and snow a trifle more.

The fourth fact that we know regard-

ing Venus is that it possesses a very dense

atmosphere-much denser, in fact, than

that of the Earth. When the planet

lies nearly between us and the Sun, it

presents the appearance of a narrow

crescent, similar to that of the .Mcon.

Unlike the Moon, however, the horns of

the crescent are greatly prolonged, some-

what like those of the crescent upon tl;1e

Turkish flag. Indeed, the horns have

sometimes been seen to unite, so as to

form a complete circle. This lengthening

of the horns is due to the atmosphere ofVenus, which so refracts the rays of the

Sun as to illuminate considerably more

than one-half of the surface of the

planet at the same time. The same effect

occurs in the case of the Earth, but to

a less extent. By measurements of the

length of the horns, the density of the

atmosphere can be computed. Careful

measurements made at Arequipa, under

unusually favorable circumstances in

1892, indicate that the atmosphere of

the planet is at least three times as

dense as our own.

A few of the earlier astronomers have

stated that Venus sometimes presents

the same appearance that in the case

of the Moon we call "the new moon in

the old moon's arms." Upon the Moon

the phenomenon is due to the close

proximity of our Earth, whose brightly

lighted surface lightens up the dark

side of our satellite. The Earth is so

remote from Yen us, however, that thisexplanation is not applicable in this

case. Various improbable hypotheses

have been offered to explain it, such as


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THE PLANET VENUS AND ITS PROBLEMS

a uniformly distributed aurora, or 'a

phosphorescent atmosphere. The true

explanation probably is that the sup-

posed observation is only an illusion,

due to the above-mentioned union of

the horns of the crescent. This union

once established, it would be impossible

for an observer to tell whether the regioninside the horns was brighter or darker

than that outside of them.

Some of the earlier observers also fur-

nished Venus with a satellite. This also

was a mistake, since no such body has

been detected by the far more powerful

instruments of modern times. Indeed,

the amount of misinformation about

fundamental facts that has been promul-

gated by various astronomers about this,

. the nearest of the planets, probably ex-

ceeds in quantity that furnished about

any other member of the solar system.

Some of the statements which cannot

yet be considered as settled are as fol-

lows: The planet revolves on its axis

once in about twenty-three hours. A

theory conflicting with this is that the

planet always presents the same face to

the Sun. Its axis of rotation lies with-

in thirty-seven degrees of the plane of

its orbit. The southern horn is blunted,

presumably b;y a high mountain, onceevery twenty-three hours. The poles are

marked by bright patches of snow.

Recognizable markings can be detected

upon its surface.

The shorter period of rotation was

determined by D. Cassini, Schroeter, and

De Vico, the longer by Schiaparelli,

Lowell, and others. Belopolski confirmed

the former by means of the spectroscope.

Lowell confirmed his own visual observa-

tions of the longer period by the samemeans. Lowell had the better instru-

ments, but his result seems less plausible

than the other. No attempt to confirm

either result has been made at any other

observatory. De Vico's determination

of the inclination of the axis has never

been confirmed. The blunting of the

southern horn. the appearance of snow

caps and of surface markings, were

looked for very carefully under the most

favora ble circumstances at Arequipa, hut

without success.

Perhaps the strongest argument in

favor of the long day is that no flatten-

ing of the planet's disk has ever been

9'7

detected at the times when it transited

the Sun. If the period of rotation was

twenty-three hours and the planet had

the most favorable possible position, the

flattening at the poles should amount

to 0.2". Although no such flattening

has been detected, yet perhaps the plan-

et did not have the most favorableposition, for the polar axis may have

been turned partly toward us at the

times of transit.

If the planet has the long day claimed

by Schiaparelli and Lowell, always pre-

senting the same face to the Sun, then

that face would be a fiery waterless

desert, while the other hemisphere would

be buried under a covering of perpetual

ice. In the desert region there could be

no moisture, except in the form possibly

of a transparent gas. There could there-

fore be no haze, no clouds. We should

see the surface of the planet through an

atmosphere clearer than that of any ter-

restrial desert. But even through a

hundred miles of our desert air the

mountains stand out clearly, showing

perfectly the difference in tint and

brightness between the rocks of which

they are composed and the snow upon

their summits. Such then should be

the case upon Venus. If such surfacemarkings exist, few astronomers have

been able to detect them, and then only

as the most evanescent markings, upon

which no two observers could agree.

Moreover, as we have already seen, the

albedo of the planet is 0.76, or practical-

ly the brightness of white paper. If we

are looking down upon a desert, we must

see one whose brightness is that of white

quartz, or crystals of salt. Possibly the

latter may be the fact, but to the writer,and to astronomers generally, the more

plausible explanation is that we are look-

ing upon a planet covered by a uniform

layer of cloud. In such a case no sur-

face markings and no polar caps could

be visible. To maintain the clouds the

planet must revolve upon its axis in a

period not very greatly exceeding that

of au)' terrestrial day. In the earlier

geological ages we are told that our

Earth was completely enveloped in cloud.

This resemblance of Venus to our own

planet is confirmed by the belief general-

ly held among astronomers that Venus

is a younger planet than the Earth.


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98 HARPER'S :MONTHLY :MAGAZINE

Had our Earth not given birth to theMoon, it is probable that our continentalplateaus would have been but little ele-vated above the sea bottoms. Indeed, thecomparatively level surface would havebeen not unlike that presented to ourgaze by the planet Mars, 'When the

Moon was born, we lost possibly thegreater part of our oceans. If so, andif similar oceans exist now upon Vcnus,we may imagine that no portion of theplanet's surface rises above the level ofthe sea; that, in short, it presents every-

The

where a liquid surface surrounded by auniform layer of cloud.

That a shoreless ocean should supportboth animal and vegetable life is per-fectly possible. We cannot conceive,however, that such life should ever at-tain a very high degree of intelligence,

and in reflecting upon our own lot wemay conclude that perhaps we have rea-son to be grateful to the Moon formore than the mere aid it gives us atpresent in lifting our great steamshipsover the harbor bars of the world.

Call

BY ALAN SULLIVAN

TURN ye again, my people, turn;

Enter my palace wild and rude,And cheerly let your camp-fires burn

Throughout my scented solitude.

The glare, the tumult, and the stressAre gone with yesterday, and we

Are children of the wilderness,

Of wonder and of mystery.

Mark how the tilted mountains lieMantled with moss and cloistered fir.

]\:[ybrother, canst thou pass them by,

Art thou not too a worshipper?

The long lake wrinkling in the wind,The breathless wood, find, over all,

Through tangled underbrush entwinedThe riot of a waterfall,

The multitudinous sounds that blendIn one vast stillness void of sound,

A slumber too divine to end,Interminable and profound.

Olose to the bosom undefiledOf her who bore mankind I press,

Receiving like a wandering child,

Her inarticulate caress.

Turn ye again, my people, turn,Enter my palace wild and rude,

And cheerly let your camp-fires burnThroughout my scented solitude.

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