"The recorded history of Mars observation dates back to the era of the ancient Egyptian astronomers." Leaves me wondering "and when was this?" Even an intelligent reader might not know if this is AD or BC.
Fixed; I added the millennium as a ballpark figure.
"Nicholas Copernicus proposed a heliocentric model for the Solar System where the planets following circular orbits about the Sun." Grammar's a bit screwy here. "where the planets following" should either be "with the planets following" or "where the planets follow". My own preference would be "in which the planets follow".
Fixed per your recommendation.
"These observations were primarily made during the time intervals when the planet was located in opposition to the Sun, at which point Mars made its closest approach to the Earth." Plural-singular disagreement. "intervals" is plural, but "point" and "approach" are singular; these should agree.
Fixed, I think.
"Better telescopes introduced early in the 19th century allowed permanent Martian albedo features to be mapped in detail." I think "introduced" should be replaced by "developed". Improved telescopes came about as a result of prolonged effort; they didn't just pop into existence one day.
Changed per your recommendation.
From "When astronomers seemingly detected..." onward, the third paragraph of the lead can be interpreted in two very different ways:
Astronomers detect water, presumably enough to support life. Dudeguy imagines canals, but they an optical illusion. Later, we learned that while there is some water in the atmosphere, there is not enough to support life.
Astronomers detect water, Dudeguy imagines canals. Both of these are optical illusions; there is no water in the atmosphere and no canals on the surface.
Without reading the rest of the article, I honestly have no idea which of these two interpretations is correct. It seems to me that the issue lies with the phrases "seemingly detected" and "these observations", whose meanings are ambiguous. "too dry" is also a bit unclear, as it could mean "some water, but not enough" or "no water at all".
Okay I think I see your point. I tweaked the wording a little and removed the "too dry" statement. Does that help any? RJH (talk)
"Yellow clouds on Mars have been observed since the 1870s, which Eugène M. Antoniadi suggested these were windblown sand or dust." Second clause is not grammar'd good. Either swap ", which" with a semicolon, or delete "these".
Removed "these"
"During the 1920s, the range of Martian surface temperature was measured and the planet was shown to have extreme desert conditions." Which means what, exactly? Hot as hell all the time? Or hot in the light and cold in the dark? Some readers may not know that deserts can get chilly at night.
Fixed
Err, not really. Did you mean to just completely delete the desert stuff? The current sentence "During the 1920s, the range of Martian surface temperature was measured." doesn't have any actual content in it... --Cryptic C62 · Talk02:19, 2 July 2012 (UTC)[reply]
Umm, does it need to say that the temperature was measured for the first time? It's intended as a simple statement of historical fact, rather than to detail out the properties of Mars (which are already covered on the Mars article). The subsequent sentence implies the "desert" conditions by saying it's arid with trace amounts of water. Regards, RJH (talk) 02:51, 2 July 2012 (UTC)[reply]
The rest of lead mentions not only the facts that observations were made, but also the interesting information that was learned as a result of those observations. The sentence in question here is the exception: it simply states that a measurement was made and nothing else. Even something as simple as "During the 1920s, the Martian surface temperature was measured; it ranged from −85 °C (−121 °F) to 7 °C (45 °F)" would suffice. --Cryptic C62 · Talk03:50, 2 July 2012 (UTC)[reply]
"In 1947, Gerard Kuiper showed that the thin Martian atmosphere contained extensive carbon dioxide." I suspect I am not the only person who has read this and thought "...so what?" It isn't clear to me why this characteristic would be noteworthy enough to mention in the lead.
I tried to clarify that the quantity found was roughly double that on Earth.
Overall, the lead does a nice job of including key points from each of the article's main sections. Happy clams!
