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There
are two equinoxes every year that take place when the sun’s rays strike earth’s
equator resulting in near equal days and nights. This year autumnal equinox is today September
23rd at 2:29 UniversalCoordinated Time. The word equinox
derives from Latin and means equal nights. Those who are interested in the
history of equinoxes please check on the post Spring Equinox at Porto Rafti. I hope you all had a good spring and summer. I wish to all of you, my friends, a good fall and winter too.
As I
have described the history of equinoxes, I thought a suitable panegyric of today’s
autumnal equinox would be brief references to two remarkable space journeys. The
first is about spacecraft Rosetta
that was launched on March 2, 2004 by the EuropeanSpace Agency (ESA) and which after 10 years and a trek of 6.5 billion
kilometers is at a distance of 285 kilometers from the comet
67P/Churyumov-Gerasimenko (C-G) and looking for a suitable landing site. In November this year it will deploy its
lander onto the C-G surface. Rosetta’s
lander named Philae will take pictures
perform physical and chemical analyses of the comet’s ice and organic material,
information that may proviBde answers to the genesis and evolution of our solar
system. This information will allow us to look back 4.5 billion years when
no planets existed and only a vast number of asteroids and comets surrounded
the Sun and formed the building blocks of our Solar System. On August 3rd the Rosetta
spacecraft took the above stunning picture of the C-G
comet. (picture
credit @ ESA)
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The second amazing expedition is NASA's
Mars Atmosphere and Volatile EvolutioN (MAVEN)
to the Red Planet. The MAVEN spacecraft, which was launched in November 2013,
arrived at Mars on Sept. 21, 2014 and began one-year mission studying the
planet's upper atmosphere. (Credit @ National Geographic/NASA)
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Humans have been fascinated with the Cosmos
since the dawn of history. Ancient
astronomers regarded comets as bad omens, a reputation that took many centuries
to overcome.
Ancient Greeks as well as other philosophers
advanced a number of different theories in their attempt to explain the nature
of comets. To some like Seneca comets
were celestial bodies like planets. To others such as Aristotle they were burning clouds or optical phenomena in the
Earth' atmosphere a view that prevailed for some 2000 years.
Our understanding of comets experienced a
dramatic leap forward with the appearance of a Great Comet in 1577, which was
as bright as Venus and had a tail forty times long the diameter of the full
Moon. Its appearance offered the Danish colorful astronomer Tycho Brahe a unique opportunity to
study them. Brahe observed
that there was no measurable parallax as the comet's position in the sky
differed very little from measurements performed at other latitudes across Europe.
According to Brahe's calculations, the comet appeared to be at least four times
farther than the Moon, so he deduced that it must belong to the heavens and not
in our Earth’s atmosphere. (picture credit @ NCAR)
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