An Extraterrestrial Visitor's Analysis of Earth Help (page 2)
An Extraterrestrial Visitor's Analysis of Earth
Suppose that you were an extraterrestrial being visiting Earth for the first time. What would you see? How would you interpret your observations? Imagine yourself in the role of the explorer/reporter assigned the task of visiting Earth and writing a report about the planet for a magazine article back home. This chapter is written from the point of view of an imaginary explorer/reporter from the fictitious planet called Epsilon Eridani 2 .
Until now in this course, measurement units such as kilometers, miles, and degrees usually have been written out in full. However, starting with this chapter, I will use more abbreviated symbology. This is the way scientists usually write such expressions, so you should get used to it too.
While the explorers from Epsilon Eridani 2 are make-believe characters, the things they see are real, although viewed from perspectives we don’t normally consider. It has been said that it is difficult to see a big picture when you are inside the frame. Let’s step outside the frame for awhile. Here is the log of the first officer of the fictitious Epsilon Eridanian exploration vessel, the Dragon .
The Blue And White Planet
As our ship approaches the planet Sol 3 , the third planet in orbit around the star that we call Sol , we are struck by the amazing blue and white colors. Previous probes have shown us that the white regions are clouds of water vapor and ice ranging in altitude from zero (at the surface) up to about 16 kilometers (km) or 10 miles (mi). The surface is well-defined, and more than half of it is liquid water. Some of the surface is frozen water; other regions show an amazing variety of features, the details of which it is part of this mission to catalogue.
We settle into a circular, polar orbit at an altitude of 500 km (300 mi). From this vantage point, over time we will be able to map in detail the entire surface of the planet using radar and optical equipment. We all look forward to the landings. We will go down two-by-two, and because there are 20 of us and we each are to be allowed only one trip, we will make 10 different landings in 10 different places on the surface.
There are regions on Sol 3 where plant life abounds, sometimes only a millimeter (less than 1/16 inch) tall and in other places upwards of 100 m (330 ft) in height. Plants also live in and around bodies of water. The largest water zones are tainted with sodium chloride (salt) and other minerals. At low latitudes, but never exactly at the equator, revolving storms occasionally occur; from our initial orbit we count five of these. The largest has a diameter of more than 1000 km (600 mi). Animal life also has been observed both on the solid surface and beneath the liquid surface. These animals exist in a range of sizes similar to those of the plants.
The most interesting structures on the planet will require extensive investigation. Their geometry suggests life forms having great intelligence some of the time and amazing stupidity at other times.
Some of these structures appear as monoliths in great congregations, perforated by holes covered over with glass. Narrow, solid strips serve as pathways for objects resembling gigantic rolling insects that go from place to place in an orderly fashion but without apparent overall purpose. Two-legged life forms have been seen entering and exiting these rolling insects. Apparently the insects are not life forms themselves but rather are vehicles designed by the life forms that enter and leave them and are intended to transport those life forms from place to place within and between the great congregations of monoliths, which, for lack of any other name at this point, I will henceforth call anthills .
I can hardly wait to land right in the middle of one of these anthills and see what happens close-up. I have already picked the one I want to check out. It is located at approximately 41°N and 73°W. According to electromagnetic signals from this anthill, it calls itself New York . There is an open, green area in the middle of this congregation of monoliths that appears ideal for a landing.
Other large insect-like vehicles have been seen flying through the air at altitudes approaching those of the highest icy clouds. When these flying vehicles are on the ground, the two-legged life forms have been seen entering and leaving them in large groups. Apparently these vehicles are designed for the purpose of transporting the life forms between anthills separated by great distances. The two-legged life forms also have been seen entering and leaving objects that slowly float on and across bodies of water, avoiding, of course, the revolving storms but nevertheless sometimes enduring wave action that would challenge the stomachs of our hardiest space travelers. Sometimes it seems as if these two-legged life forms use their vehicles for the sole purpose of having a violent ride!
Year, Day, And Seasons
The equatorial plane of Sol 3, which the two-legged inhabitants call Earth , is tilted by approximately 23.5 degrees with respect to the plane of its orbit around the parent star Sol, which they call the Sun . This results in considerable seasonal variations in the weather that become increasingly dramatic as the latitude increases. The hours of daylight and darkness are always equal at the equator, but fluctuations become greater and greater as one goes nearer to the poles. North of 66.5°N and south of 66.5°S, there are periods when the Sun stays above the horizon for days at a stretch. At the poles themselves, the daylight period lasts for fully half the year, and the darkness period lasts for the other half.
There are about 365.25 solar days in each Earth year. It is difficult for me to describe the length of the Earth day except to say that the two-legged creatures divide each day into 24 equal units called hours . Each hour is divided into 60 minutes, and each minute is divided into 60 seconds. Fractions of a second are expressed in decimal form. For some reason, most Earth inhabitants divide the solar day into two 12-hour segments called and Some of their scientists use an undivided hour system that runs from 0000 (zero hours, zero minutes) to 2359 (23 hours and 59 minutes) and then starts over again at 0000 in the middle of the dark period.
The Earth is farthest from the Sun (that is, it is at aphelion) in the month called July and is closest to the Sun (that is, at perihelion) in the month called January . The mean distance of the Earth from the Sun is 149.6 million km (93 million mi). The variation in orbital radius is only about ±1 percent. The Earth’s greater distance from the Sun in the northern-hemispheric summer results in less solar irradiation over the planet’s greatest land masses at that time. However, this effect is balanced by the fact that the season is lengthened; Earth moves more slowly around the Sun at that time (Fig. 8-1). Conversely, the Earth’s lesser distance from the Sun during the northern-hemispheric winter produces more solar irradiation, but the season is shorter because the Earth moves faster around the Sun.
The earth’s axis precesses , or wobbles, slowly like the axis of a spinning top. Every 25,800 Earth years, the axis describes a complete circle whose angular radius is 23.5 angular degrees on the celestial sphere. This means that in 12,900 years, Earth will be closest to the Sun in July and farthest from the Sun in January (Fig. 8-2). It is difficult to say what effect this might have on the overall climate of the planet. There is much more land mass in the northern hemisphere than in the southern; land masses heat up and cool off more rapidly than the oceans. This could have a tremendous cumulative effect when the northern-hemispheric summer is shortened and the winter is lengthened. It is known that the repeated cycles of glaciation that take place on our own planet, Epsilon Eridani 2 (the second planet in orbit around the star Earth inhabitants call Epsilon in the constellation Eridanus), also have taken place on Earth; axial precession might be a contributing factor to these so-called ice ages.
Practice problems of this concept can be found at: The Planet Earth Practice Problems
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