FAQ-PlanetaryProperties

1.Describe the shape of the earth.

It is an oblate spheroid. Meaning that radius from the equator is longer than radius from the poles

2. What is the earth’s radius and volume?

The radius of the Earth is 6371 Km (usgs.gov)

Its volume is therefore approximately
V = (4/3)*pi*r^3 = (4/3)*pi*(6371 km)^3 = 1.08x10^12 km^3

The earth is approximately 6,000,000,000,000,000,000,000,000 (6E+24) kilograms.
Newton showed that, for spherical objects, you can make the simplifying assumption that all of the object's mass is concentrated at the center of the sphere. The following equation expresses the gravitational attraction that two spherical objects have on one another:

F = G * M1 * M2 / R2

• R is the distance separating the two objects.
• G is a constant that is 6.67259x10-11m3/s2 kg.
• M1 and M2 are the two masses that are attracting each other.
• F is the force of attraction between them.

Assume that Earth is one of the masses (M1) and a 1-kg sphere is the other (M2). The force between them is 9.8 kg*m/s2 — we can calculate this force by dropping the 1-kg sphere and measuring the acceleration that the Earth's gravitational field applies to it (9.8 m/s2).
The radius of the Earth is 6,400,000 meters (6,999,125 yards). If you plug all of these values in and solve for M1, you find that the mass of the Earth is 6,000,000,000,000,000,000,000,000 kilograms (6E+24 kilograms / 1.3E+25 pounds). (http://science.howstuffworks.com/question30.htm)

4. How much of the earth’s surface is covered by water?

71% of the Earth's surface is covered by water. (Marine Biology 3rd ed. 2000 - Castro & Huber)

5. What is the volume and weight of the hydrosphere?

Area covered by oceans: ~361,132,000 km^2; avg depth of ocean: 3.72 km. Multiply together = 1.3434*10^9 km^3, roughly. Data from http://www.eoearth.org/article/Ocean
Denisty of seawater = 1028 kg/m^3. D=M/V. Extrapolating…hydrosphere has mass of ~1.38*10^21 kg

6. What is the volume and weight of the atmosphere?
7. What is “mean” sea level and what are the extreme deviations from this datum?
8. Describe the hypsometric curve and discuss its tectonic implications.

A hypsometric curve is essentially a graph that shows the proportion of land area that exists at various elevations by plotting relative area against relative height. In the hypsometric curve of the total Earth surface there exist two maxima of frequencies—at the 100-metre (109-yard) and the 4,700-metre (5,140-yard) elevations, which correlate with the mean level of the lowland continental areas and the deep-sea floor. This aspect of the Earth’s surface, revealed by hypsometric analysis, supports the theory of a crust consisting of simatic (peridotitic, specific gravity about 3.3) materials under the oceans and of sialic (granitic to gabbroic, specific gravity about 2.7) materials of the continents (britannica.com)

9. Distinguish between sidereal and solar time.

Solar time is measured by the apparent diurnal motion of the sun, and local noon in solar time is defined as the moment when the sun is at its highest point in the sky (exactly due south or north depending on the observer's latitude and the season). The average time taken for the sun to return to its highest point is 24 hours. During the time needed by the Earth to complete a rotation around its axis (a sidereal day), the Earth moves a short distance (around 1°) along its orbit around the sun. Therefore, after a sidereal day, the Earth still needs to rotate a small extra angular distance before the sun reaches its highest point. A solar day is, therefore, around 4 minutes longer than a sidereal day. Sidereal time is a measure of the position of the Earth in its rotation around its axis, or time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical to, the motion of stars. They differ by the precession of the vernal equinox in right ascension relative to the stars. Earth's sidereal day also differs from its rotation period relative to the background stars by the amount of precession in right ascension during one day (8.4 ms). ( Wikipedia: http://en.wikipedia.org/wiki/Sidereal_time )

10. Why is the earth’s rotation slowing down and what might be some geological consequences of this?
11. The earth’s angular velocity and angular momentum vectors are not aligned. Why?
12. What is the “solar constant”, why might it vary, and what are climate implications of a variable solar constant?

The solar constant is the total amount of energy received from the sun per unit time per unit area exposed normally to the Sun's rays at the average Sun-Earth distance and outside of the Earth's atmosphere (http://www.ngdc.noaa.gov/stp/SOLAR/ftpsolarirradiance.html).
It varies due to Earth's changing distance from the Sun and may also be affected by the Sun's radiation output. The climate implications of a varying solar constant are the seasons, first and foremost.

13. Why do we have seasons and are there seasons on other planets and moons of our solar systems?

Seasons on Earth are created largely in part due to Earth's tilt and also the varying distance between the Earth and Sun. Earth's orbit is con-circular, therefore Earth will receive more solar radiation when it it nearer to the Sun compared to when it is farther away. Secondly, Northern and Southern hemispheres have differing seasons because when one is tilted towards the Sun it receives more solar radiation than the other hemisphere (summer), which is tilted away from the Sun (winter).
In order for a planet or moon/satellite to have seasons it must have an axial tilt roughly between 10 and 45 degrees. However as the distance from the Sun increases, solar radiation diminishes and length of seasons increases, so the variation between seasons will be slight and infrequent.

Andreas: Does anyone else see the contradiction in the above statement? [tilt vs. distance]

14. Give examples from your research area of adiabatic, diabatic, isentropic, and irreversible processes.

page revision: 10, last edited: 17 Sep 2008 01:36