Instant Message
Email
Phone
In Person
Astronomy & Cosmology II
  Galileo
Galilei (1564-1642), first to devise and use a telescope for astronomical
observations, discovered the moons of Jupiter, and the motion of sunspots
across the solar disc - sign of a less than perfect sun, which also rotated!
His many observations confirmed the Copernican theory of the motion of
earth and planets around the sun, and brought him in conflict with the
Inquisition; for such heresy he spent his last years under house arrest.
Here he is honored on Italian and Czech stamps: eppur si muove! |
 |
  Johann Hevelius (1611-87) was a wealthy brewer in Danzig who dedicated his life and fortune to the study of astronomy. He built enormously long telescopes and other outsize apparatus on the roof of his house (Newton's reflecting telescope had not yet been invented). He mapped and named craters and mountains on the moon and in 1647 published Selenographia, the first illustrated work of astronomy dealing exclusively with the moon. He also published a stellar atlas, Firmamentum Sobiescianum, observed and mapped nebulosities including the Andromeda nebula, and recorded several decades of sunspot observations. These Polish stamps show Hevelius from a portrait in Selenographia superimposed on a chart of constellations, and also with his six foot radius brass sextant on the roof of his house. His celestial atlas Uranographia of 1690 may be viewed on the website of the Brera Astronomical Observatory. |
 Newton's law of universal gravitation applies not
only to apples falling from trees, but also describes the relationship
of mutual attraction between planets and celestial bodies in the universe.
(See also Mathematics
and Computation I.) |
|
 Since
Newton's time the heliocentric system of Copernicus and Kepler in which
the earth and the other planets moved in elliptic trajectories around
the sun was generally accepted by astronomers. Observed irregularities
in the orbit of Uranus led the French astronomer Urbain Le Verrier (1811-1877) to suspect the presence of a planet as yet undiscovered,
whose gravitational pull on Uranus caused the discrepancies in orbit.
He communicated his calculations to the German astronomer Johann
Gottfried Galle (1812-1910), who observed the new planet, Neptune, just
where Le Verrier had predicted. |
|
   |
 The return of Halley's comet in 1986 was an event that captured the imagination
and also occasioned an outpouring of philatelic materials around the world.
The British possession St Helena was the first to weigh in with a set
that commemorates astronomer Edmund Halley's (1656-1742) visit in 1677
to that remote island in the South Atlantic to prepare the first stellar
atlas of the southern hemisphere. Most spectacular in this set is the
contemporary reproduction of the comets image from that comic strip of
the Norman Conquest of England in 1066, the Bayeux Tapestry, while Halley's
sextant on the stamp below could pass for a quadrant. But only a few years
after this visit, Halley speculated that the comet of 1682 had actually
been observed before at regular intervals. He calculated the orbit of
this comet now named for him, and correctly predicted its return in 1758,
in a first application of Newton's laws of motion. The comet has returned
twice this century, in 1910 and 1986, or "twice in a lifetime" for a lucky
few. The Australian stamp at upper right shows a plot of the earth's
and the comet's trajectories around the sun over the image of a large
radiotelescope. Britain was also among the nations to mark the comet's
return with commemorative stamps and investigated it via the space
probe Giotto. Notice how Orion appears "upside down" to observers in
Antarctica for British Antarctic Territories. The PRC stamp at right
shows the comet streaking from right to left over the curved earth and
over some mysterious symbols, whose meaning is explained below in notes
to the Stamp Index. |
 |
  |
A solar eclipse takes place when the new moon passing between the sun and the earth blocks the solar radiation and casts its shadow on the earth. It can be total, partial, or annular. Total eclipses here commemorated were observed in Mexico in 1970, and the Philippines in 1995. The solar eclipse of August 1999 cut a swath from the extreme eastern shore of Canada across the Atlantic Ocean, then Great Britain and Central Europe, and was thus viewed by millions of enthusiastic observers. Postal entities followed the cue and issued many stamps and special cancellations. Shown here is a French stamp of totality, with a splendid corona framing the eclipsed solar disk. The progression of the phenomenon is shown counterclockwise from the upper right corner of the stamp. The new monetary unit of the European Union, the Euro, has also crept into the upper right corner. An earlier eclipse stamp from Mexico in 1942 honors the inauguration of the astrophysical observatory in Tonanzintla that year. Among the more interesting stamps featuring the eclipse of August 1999 is from Romania. It has a tag with a diagram, not drawn to scale, showing the alignment of sun, moon, and earth necessary to produce an eclipse. The stamp itself shows the corona of an eclipsed sun, and in a rectangle a map of Romania with the projected swath of the eclipse across it. The legend "total solar eclipse" and the date appear in English on the tag and in Romanian on the stamp itself, while the date of issue is 1998 - earlier than the event perhaps in anticipation of philatelic demand. The USPS in 2000 issued a minisheet called Exploring the Solar System of five $1.- pentagonal stamps showing various aspects of the sun, including the eclipse below, right. |   |
  |
 Sunspots appear as dark spots on the glowing disk of the sun, near the sun's equator, and they seemingly travel across the disk over a period of days. They were probably already observed by the ancient Chinese who did not known what to make of them. When telescopes became available in Western Europe, in the 17th century, astronomers such as Galileo, Scheiner, Herriot, and Goldsmid observed them more systematically and sketched their shape and position on the solar surface. Galileo determined that they were part of the solar surface from observing their changing shape as they disappeared beyond the solar limb. Counting them over periods of centuries has shown that their numbers increase and decrease over a period of eleven years, which is known as the solar cycle. The periods of high solar activity correspond to times of maximum sunspots, when solar flares explode near sunspots whose magnetic fields become unstable. Ionized gases are flung into space in a coronal mass ejection and cause geomagnetic storms and auroras near the earth, interrupting satellite and other electromagnetic communications. The period of minimum sunspots is known as a solar minimum, when activity is much reduced. The years 1964-65 were designated as the Year of the Quiet Sun, as commemorated on the DDR stamp at left. |
 
During the International Geophysical Year, advances in rocketry both in the United States and the Soviet Union had made it possible to explore space beyond the earth’s atmosphere. The Explorer spacecraft, launched in 1958, was designed by James van Allen (1914-2006) to measure the distribution of charged particles encircling the earth by means of a Geiger counter. Earlier, in 1957, Sputnik I likewise explored these regions which were found to be torus-shaped and were subsequently called the van Allen belts. Energetic particles streaming from the sun are captured in the earth’s magnetic field and constrained to spiral along the field lines emanating from both poles. Our magnetosphere is not symmetrically shaped, being deformed by pressure from the solar wind and elongated in the other direction (see solar wind stamp above). Continuing satellite exploration has found that the other planets are also magnetized and exhibit radiation belts. Hannes Alfven (1908-1995) a Swedish Nobel laureate in Physics (1970) contributed much to the understanding of the behavior of the radiation belts, auroras, and effects of magnetic storms on the earth’s magnetic field, and the plasmadynamics of the galaxy. |
  |
The auroras near the north and south magnetic poles, bright pulsating bands in the night sky at altitudes ranging from 70 to 300 km, are due to high energy particles originating from solar flares on the sun, which then collide with atmospheric molecules, causing them to emit light. Most of these charged particles are deflected by the earth's magnetic field, which protects the atmosphere from being destroyed by the energetic particle flux. The Aurora Australis and Antarctica are shown on a 1965 stamp, commemorating a Japanese scientific expedition. The distortion of the earth's magnetic field, or magnetosphere, described above by the so-called solar wind is shown in a stamp from the British Antarctic Territory on the left. The Aurora Borealis also appears on a Soviet stamp honoring the International Geophysical Year 1957-1958. Last but not least, the small stamp from Greenland packs a mighty punch, showing a northern lights display between the Big Dipper and Polaris. |   |
 |
