This entry will be wikipedia-heavy, be-warned.
One of the best ways to demonstrate the existence of sexism in science is to ask people "How many scientists can you name?" and then ask, "How many women scientists can you name?"
I don't do very well here, because off the top of my head, without looking it up, I get three: Jane Goodall, Marie Curie, and Roberta Bondar. They're all on the list because of entirely self-centred reasons: Goodall because I like biology, Curie because she's french and was a bit loony about those magic rocks of hers, and Bondar because I did a project on her in junior high, she's Canadian, and a neurologist (which is what I wanted to be once upon a time).
Three is definitely not enough (I'm not counting bloggers that I read, because for most of them, like Isis, I don't know their real names). I mean, I can count ten male scientists right away.
Well, I am now able to add a fourth name, the luminous Caroline Herschel, "Lady Astronomer". I'm reading a great book about the scientific trailblazers of the late 18th and early 19th centuries called "The Age Of Wonder: How The Romantic Generation Discovered The Beauty And Terror Of Science" by Richard Holmes, and he devotes a lot of time to Caroline Herschel and how she helped to shape astronomy in ways that we are still affected by today.
She was the sister of William Herschel, most celebrated for his discovery of Uranus, which was the first new planet to be discovered in our solar system since Jupiter, thousands of years earlier, and it's very reasonable to assume that William would not have found his great success had he not had his sister by his side. Their life stories are deeply intertwined. William was much older than she was, and rescued her from a bleak life with her neglectful family in Germany, whisking her away to England where he was established as a musician and was just beginning to delve the depths of the skies. Together, they developed a strategy of "sweeping" the heavens, methodically using their self-created telescopes to methodically scan the skies, cataloguing every star and nebula and making notes of any unusual thing they saw.
One of William Herschel's more famous achievements was his giant, 40 foot telescope, basically the Hubble Telescope of its day (with the same history of technical difficulties), but even before the 40-footer was made, the telescopes he used most often were unweildy and required great help from an assistant for him to use them to any effect. And for William Herschel, the only assistant who would do was his beloved sister Caroline.
It would have been impossible for Caroline not to learn something about astronomy after assisting her brother night after night, and over time she began to be recognized as a talented astronomer herself: she discovered several comets and received a lot of recognition from the Royal Society and other groups, which was nearly unheard of for women in those days (and really, has that much changed? See my opening paragraph).
While Age of Wonder is a great read all the way through (er, actually, not finished yet, so the last third could be terrible, I guess), the chapters devoted to Caroline and William are the ones that really grab me, and give me a better sense of what the world was like in that place and time. I'm grateful to Richard Holmes for including her story and if anyone out there has more books about women in science, let me know! Because, 4 female scientists on my list is still pitiable (er...and don't ask me about people of colour in science. Which you won't. Because other than Neil deGrasse Tyson we know they don't actually exist).