Lecture Notes for the Midterm
History of Mars exploration
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History of Mars observation from Earth
- The "eyeball method":
- See Viewgraphs:
"Early explorations."
- Early astronomer/astrologers from Mesopotamia (Iraq), India, China,
Egypt, and Greece noted and described the regularities in star motions across
the sky: They also noticed that five "stars" were not well-behaved, that they
moved faster or slower than the "others," and even went backwards or
retrograde. These five wanderers ("astra planeta") were
Mercury, Venus, Mars,
Jupiter, and Saturn.
- The ancient Indians mentioned a retrogation (a period of seemingly
reversed motion) of Mars in 3,010 BCE, in the
Mahabharata (the saga was put together over a long time, first being
mentioned in the 4th century BCE, the epic poem describing a war said to have
happened in the late fourth millenium BCE)
- The Chaldean astronomer/astrologers of ancient Mesopotamia compiled a
database of astronomical observations that they tried to correlate with
different social, economic, and environmental events -- Mars is often
mentioned in these tablets, the Enuma Anu Enlil, which date back to 652
BCE and continued until 60 BCE. Here is a sample: "That month, the equivalent
for 1 shekel of silver was: barley [lacuna] kur; mustard, 3 kur ... At that
time, Jupiter was in Scorpio; Venus was in Leo, at the end of the month in
Virgo; Saturn was in Pisces; Mercury and Mars, which had set, were not
visible."
- Chinese dynastic historians noted conjunctions of planets including Mars
back to the fourth century BCE
- The Mayans from 1800 BCE to the time of Columbus developed elaborate and
accurate calendars, especially during their Classic phase from 250 - 900 CE.
The Spanish destroyed most of their written records, but four priestly
handbooks, or codices, survive. The Dresden Codex includes a "Mars Beast
Table" that predicts Mars' motions and retrogations.
- The ancient Greeks were really bugged by Mars' and other planets'
occasional retrograde episodes and came up with various schemes.
- Aristotle (lived ~384-322 BCE) observed an occulation of Mars by the Moon
around 356 or 357 BCE: the Moon passing in front of Mars. He figured out that
Mars had to be farther out than the Moon.
- Aristarchus (~310-230 BCE) had come up with the idea that the sun was the
center of the solar system and the planets revolved around it: He didn't get
too far with this seemingly nutty notion.
- Hipparchus (~190-120 BCE) described the five planets' orbits as
"deferents" around the earth
- Ptolemy (~90-168 CE) added little circular sub-orbits, or
"epicycles"
along the deferents to account for the retrograde episodes.
- The collapse of Græco-Roman civilization put an end to work on Mars
or
any other science for a long time.
- The rise of Islam rejuvenated Arab culture and supported mathematical and
scientific work, including mastery of the Greek classics and developments on
them. Algebra and the Arabic numeral system were developed, and Ptolemy's
system was edited by Ibn al-Haytham around the 10th century and Nasir ad-Din
at-Tusi in the late 13th century to make it better able to predict planetary
motion. These achievements were brought to Europe at least partly because of
the Crusades.
- Europeans in the throes of the Renaissance and their re-introduction to
Classical era and Arab science, got into the swing of things, too:
- Mikołaj Kopernik or Nicholas Copernicus argued in 1543 that the
planets' motion made more sense if Earth was itself a planet and rotated about
a north-south axis while revolving with the other planets around the Sun. His
observations squared better with Aristarchus He assumed that all six planets'
orbits were perfect circles, which meant that there were still little
discrepancies. He was forced to account for those by keeping Ptolemy's
epicycles. This was an absolutely revolutionary idea to Christendom: That
Earth wasn't the center of creation.
- Tyge Brahe, Latinized as Tycho Brahe, was a dedicated and obsessive
observational astronomer in Denmark, Sweden, Germany, and Bohemia, who lived
from 1546 to 1601. Brahe wasn't much into theory, but he was a really
original engineer who built new observational instruments for measuring the
positions of objects in the sky. He instituted a program of nightly
observation and trained others in the art. He had kept meticulous records of
the precise locations of various stars and the planets in a huge database. He
often focussed on Mars because of its seeming anomalies of motion, but he
never theorized from his observations. He was aware of Copernicus' work, but
found it implausible because it required the abandonment of Aristotelian
physics.
- Johannes Kepler came to work with him toward the very end of his life, in
1600, and studied 20 years of his records, trying to make sense of them. He
found himself in agreement with Copernicus, which annoyed Brahe no end. So
Brahe decided not to share all his data with Kepler but set him working only
on the data concerning Mars, his toughest problem. Kepler found that the best
way to make sense of Mars' orbit was to apply Copernicus' heliocentric theory
but relax the assumption about a perfectly circular orbit. In 1609, years
after Brahe had died (some even speculate that he offed Brahe to get hold of
his data), Kepler posited an elliptical orbit for Mars and three laws of
motion and got rid of the epicycles.
- The orbits of the planets are ellipses, with the Sun at one of the
two
foci of the ellipse.
- The line connecting the planet to the Sun sweeps out equal areas in
equal
times, so it slows down at aphelion and speeds up at perihelion
- If you compare two planets' orbits, the ratio of the squares of their
revolutionary periods is the same as the cubes of their semimajor axes: The
period a planet requires to go around the Sun increases rapidly with the
radius of its orbit. The farther out they are, the drastically longer their
years are. That is, P12/P22 =
R13/R23
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![[ orthographic image of Mars on a black background ]](https://home.csulb.edu/~rodrigue/mars/marsblackbg.jpg)
![[ Olympus Mons seen at oblique angle that gives a 3-d sense ]](https://home.csulb.edu/~rodrigue/mars/olympusmons3d.jpg)
![[ Mars explorer ]](https://home.csulb.edu/~rodrigue/mars/marsexplorerpainting.jpg)
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![[ image of Mars ]](https://home.csulb.edu/~rodrigue/mars/marsatlas.gif)