Earth’s orbit

The sun radiates approximately as a blackbody, with an effective temperature of about 6000 K. The total solar flux is 3.9 x 10 W. Using Wien s law, it has been found that the frequency of maximum solar radiation intensity is 6.3 x 10 s (X = 0.48 /rm), which is in the visible part of the spectrum 99% of solar radiation occurs between the frequencies of 7.5 X 10 s (X = 4/um) and 2 x 10 s (X = 0.15/um) and about 50% in the visible region between 4.3 x 10 s (X = 0.7 /rm) and 7.5 X 10 s (X = 0.4 /Ltm). The intensity of this energy flux at the distance of the earth is about 1400 W m on an area normal to a beam of solar radiation. This value is called the solar constant. Due to the eccentricity of the earth s orbit as it revolves around the sun once a year, the earth is closer to the sun in January (perihelion) than in July (aphelion). This results in about a 7% difference in radiant flux at the outer limits of the atmosphere between these two times. 

Adaptations to Habitats. Because of Eaith s geom-etiyf and the position of its axis, the equator receives more solar energy per unit area than the polar regions. Because Earth s axis is tilted relative to the plane of Earth s orbit around the Sun, this angle of incident radiation varies seasonally. These factors, combined with Earth s rotation, establish the major patterns of temperature, air circulation, and precipitation. 

Much of the variation in these time series for the past 700 kyr can be described by a combination of a 100 kyr cycle plus additional cycles with periods of 20 and 40 kyr. This result immediately suggests that the ice-age cycles are caused by variations in the amount and seasonality of solar radiation reaching the Earth (insolation), because the 20, 40, and 100 kyr periods of climate history match the periods of cyclic variations in Earth s orbit and axial tilt, line hypothesis that these factors control climate was proposed by Milutin Milankovitch in the early part of the 20th century and is widely known as "Milankovitch Theory." It is now generally accepted that the Milankovitch variations are the root cause of the important 20 and 40 kyr climate cycles. The 100 kyr cycle, however, proves to be a puzzle. The magnitude of the insolation variation at this periodicity is relatively trivial, but the 100 kyr cycle dominates the climate history of the last 700 kyr. Further,... 

Fig. 18-2 Orbital parameters that control the seasonal and annual receipt of radiation at the Earth s surface. The Earth s rotational axis tilts and wobbles as shown. The eccentricity of the orbit is dp — d )/ (dp + da) which is zero for a circle but for the Earth s orbit is sometimes as large as 0.06. (After Hartmann (1994, p. 303) and Turekian (1996, p. 80).)...

So a star with a parallax angle of 0.1 arcsec is at a distance of 10 pc, which can be converted to SI units by knowing the Earth s orbit. One parsec is 3.26... 

Gyr ago. There is evidence that it was reheated as a result of a shock event about 4 Gyr ago and water flowed through it, depositing carbonate globules. It was ejected form the Martian surface by another impact event and orbited the Sun on its own for about 16 million years before intersecting the Earth s orbit and landing some 13000 years ago, impacting into the ice of Antarctica where it was found. 

These applications show how easy it is to modify a program, once it has been developed, to explore such questions. Another application, not undertaken here, would be to explore Milankovitch perturbations in the Earth s orbital parameters, eccentricity, obliquity, and date of perihelion. These parameters are specified as constants at the beginning of the program, and it would be simple to change their values as predicted by astronomical calculations, in order to see how the seasonal variation of temperature is affected at various latitudes. 

Hays JD, Imbiie J, Shackleton NJ (1976) Variations in the earth s orbit pacemaker of the ice ages. Science 194 943-954... 

Geologists in the nineteenth century deduced that the Earth has experienced several ice ages, during which the ice sheets that cover the poles today reached much farther afield. In 1930 the Serbian mathematician Milutin Milankovitch showed how changes in the shape of the Earth s orbit around the Sun could trigger an ice age by altering the seasonal distribution of sunlight at the planet s surface. There are three cyclic variations in the orbit, with periods of 23,000, 41,000, and 100,000 years. The interplay of these Milankovitch cycles produces a complex but predictable and slow variation in climate over hundreds of thousands of years. 

The classical work of Milankovitch, further elaborated on by other authors, focuses on the study of the correlation between climate change and the Earth s orbital variations—in particular, the build-up and decay of glaciations [65]. 

Michelson and Morley [50] used an interferometer to measure the speed of light along two orthogonal directions parallel and perpendicular to the earth s orbital speed. They found that the speeds differed by a value somewhere in the range between 5 and 7.5 km/s. Michelson and Morley were extremely surprised because they expected to observe a difference of 30 km/s. At that time they had no plausible explanation for their empirical observation and decided to interpret the outcome of the experiment as a null result no difference in speed along both direction (apparently, the reason for this choice was that Fresnel s theory predicted no difference). 

Numerous unsuccessful measurements were made to determine the motion of earth in the ether. These measurements were not able to give results compatible within the framework of classical Newtonian mechanics, even though that the earth has an orbital velocity v0 30,000 m/s (where v0 is velocity of the earth to the ether). In 1887 Michelson and Morley also determined the earth s orbital velocity by their precision interferometer [11], The updated arrangement of Michelson-Morley experiment (M-M experiment) can be seen in Fig. 1. 

Figure 1. An up-to-date arrangement the of Michelson-Morley experiment. Here LASER means the source of light, BS means beamsplitter, Ml and M2 are mirrors on the end of arms, PD is the phase detector (interferometer), and v is the earth s orbital velocity, which is regarded as the inertial motion for short time periods.

Of course, the Sagnac-type experiments were not made in a perfect inertial systems. The earth s orbital motion around the sun is also a noninertial system. But the circumference velocities in both cases are extremely low, v/c[Pg.398]

The reaction also produces extremely high temperatures—around 6,000°F (3,300°C). The water vapor produces the extra lift the shuttle needs to get out of Earth s orbit. Like the solid rocket boosters, the external tank separates from the shuttle when the fuel is gone. Unlike the boosters, by the time the external tank is released from the shuttle, it is outside of Earth s atmosphere and it burns up as it reenters the atmosphere. 

At the end of this section, two final points merit some attention. The first one concerns the location of the parent bodies of the chondrites. The asteroid belt between Mars and Jupiter is one possibility favoured by many authors, but some other possibilities exist (such as the families of asteroids crossing the earth s orbit). Asteroids themselves are of many different types and some of them are probably extinct comets (after too many passages at the perihelion). Some chondrites could be fragments of these extinct comets, but this hypothesis is not the most probable one. People interested in this problem will find information in Refs. 2, 5 and 9. 

Eccentricity of the Earth s orbit, which varies from almost circular to strongly elliptical with a periodicity of about 95,800 years (these changes modulate precession). 

The Earth s orbital chirality (EOC) is mainly created by both the Earth s right-handed helical rotation around its spin axis and the Earth s right-handed helical revolution around the Sun [8]. Finally, spiral galaxies show axial symmetry and an intrinsic 2D chirality [9]. 

Y.J. He et al., Effect of earth s orbital chirality on elementary particles and unification of chiral asymmetries in life on different levels. Med. Hypotheses 54, 783-785 (2000)... 

---