Centrifugal forces due to the rotation of the Sun may cause the solar wind and the interplanetary magnetic field to vary away from the solar equatorial plane. Consequently, space probes that journey out of the ecliptic are important for filling in the details that cannot be provided by the usual interplanetary missions. The motion of […]
The AURORAE BOREALIS and AUSTRALIS have been associated with magnetic activity since the eighteenth century. Most of the light in these displays is produced by excitation and ionization of the upper atmosphere at high latitudes by an influx of electrons with energies about l0keV. Disturbances of the magnetic field con¬figuration within the magnetotail energize these […]
SOLAR STORMS, described above, are spectacular outbursts due to the sudden transformation of a considerable amount of energy (about 1026 joules) into electromagnetic and charged-particle radiation within an hour or so. A typical event is a solar flare, which, apart from the burst of radio, optical and X-radiation, releases electrons and protons with energies that […]
The absorption of solar Lyman-a (121.6 nm) and X-radiation by the upper atmosphere of the Earth results in the ionized regions known as the ionosphere. The ions and electrons are here present to such an extent that radio-wave propagation is seriously affected and indeed reflection occurs at long wavelengths. The D-REGION lying between about 60 […]
The continuous expansive motion of the coronal gas gives rise to the SOLAR WIND. At the distance of the Earth its velocity is normally about 400 km s”1, the particle density about 107nr3, and the temperature approximately 105 K. Even though the total outflow of material from the Sun is about one million tonnes per […]
The Sun And Earth The radiations from the Sun influence the Earth and planets in many ways apart from the obvious effects of heating and illuminating their surfaces. The study of the interactions between the Sun and Earth is a branch of astronomy termed solar-terrestrial relations. The short-wavelength photons from the Sun have sufficient energy […]
As early as 1900. a British physicist, Sir Oliver Lodge, attempted to detect radio waves from the Sun. His failure to do HO can be attributed mainly to the primitive equipment then available. Marconi, in 191(5, and various radio enthusiasts thereafter, surmised that the static disturbances might be of solar or cosmic origin. Military investigations […]
Brilliant Hashes of light in the solar atmosphere, lasting less than an hour, or even perhaps only a few seconds, are named SOLAR. FLARES. The brightest are visible in white light, but they are easier to see in the light of hydrogen or calcium lines. A flare is a highly concentrated, explosive release of energy, […]
An active region on the Sun (one is shown in figure 8.23) includes not only sunspots but related phenomena: plages, prominences, faculae, and flares, to name but a few. One feature common to all these natural phenomena is the strong magnetic field. PLAGES are highly disturbed zones in the chromospheres. They usually appear before the […]
SUNSPOTS are the sole sign of solar activity that is occasionally detectable to the eye. Known since antiquity, according to Greek sources, they were rediscovered by Europeans in 1611, after Galileo’s epochal application of the telescope to astronomical investigations. Despite the Greek knowledge, the European school of natural philosophy steadfastly held the Sun to be […]