I found out recently that one problem with the validity of astrology is that the alleged influence of the planets Uranus, Neptune, and Pluto were not accounted for in old writings; the telescope was invented around the time of the Renaissance, and the outer planets, Uranus (1784), Neptune (about 1850), and Pluto (1930) were discovered long after this.
I bet this opens up a can of worms between the astrologers and their debunkers.
This along with the procession of the earth’s axis, which Cecil has addressed in his column.
To know about other points against astrology you can go to the Astrology Defense Kit.
Quite some good questions to ask an astrology believer.
I agree! I wish that website had been around for Cecil to use when he tackled the topic in Return of the Straight Dope. 
Fun thing to do in a college astronomy course:
About half way through the course, when the professor is talking about the internal structure of the sun or some similarly dry topic, raise your hand and ask, “So when are we going to learn how to read people’s horoscopes?”
That’s a great site, and some good questions.
My roommate did his master’s thesis on the use of astrology in medieval medicine, and he has the following argument to add:
The body of (supposed) knowledge that comprises astrology does not, and apparently has never, claimed to be due to divine revelation. It is instead purported to be observationally determined. Astrologers will tell you that the newspaper horoscopes are nonsense because to make “real” predictions you have to know the details of the subjects birth: the exact day and, if possible, hour. The combinations are huge; each planet is in a particular sign of the zodiac, and a particular house. This is an enormous number of combinations, even for the seven medieval bodies -sun, moon, mercury, venus, mars, jupiter, and saturn.
So for astrology to be observational it would involve keeping meticulous records of which particular one of these combinations went with which particular person, and what that person turned out to be like, for literally hundreds of thousands of people over many, many lifetimes, and of course you somehow have to normalize out the effects of the local environment, too. The record keeping and statistical analysis tools required were, quite simply, unknown to anyone in the ancient world.
Astrology cannot be an observational science on the face of it. So where does the knowledge come from?
[We realize, of course, that it comes from a pre-Copernican cosmology and a belief system that imbued objects like planets with associative characteristics - the moon is associated with maidens and the like - and allowed for sympathetic magic to operate. But Astrologers rarely admit this.]
Thanks! I’m gonna print that thing up and memorize it any time I meet any fools who believe astrology.
NOTE: What we now call “astrology” used to be known as “astronomy” and vice versa. The meanings of words are not fixed and will change over time, whether we want them to or not. EXAMPLE: The meanings of “flammable” and “inflammable” are starting to reverse because too many people are just plain ignorant.
>< DARWIN >
__L___L
Boy, I know a LOT about astrology. From the time I was 13 til I was 33, I was hooked on it. I did peoples horoscopes(for free), and practiced it all the time. Theres no getting through to people who believe this. Of course, I knew it wasn’t really true(every time it said I was going to have a great day, I was home from school sick). Its a pyscological thing. Make it up as you go along. People want to believe you can predict what will happen. I don’t even Want to know whats going to happen!
[OK, this is my first post, hope it works]
There is another thing to consider: The “better” astrologers want to know the time you were born. Is this local time? Real noon in the eastern time zone is the same as real noon in Philidelphia. Here in Boston, real noon happened about 20 minutes earlier. And this is not even considering the equation of time, where mechanical clocks may be off by as much as 16 minutes.
Responsible astrologers would ask not only the exact time you were born, but in which city (and in which time zone). Or doesn’t that matter?
And would the average astrologer even know what Venus looks like? Do they look up into the sky and say, “Hey, that’s Venus”, or would they just think it’s a really bright star? I would bet the latter.
[hijack]Back in my university days the astronomy professor (I working in the astrophysics research lab as a programmer, my first job in technology) would always start the first class of the year with an explanation of the difference between astronomy and astrology. He had class withdrawl slips with him. Every year without fail at least one person would withdraw (the record was 5 people)! After that, he would always say “Any further questions on astrology will result in a failing grade”.
I went up to an astrology booth at a psychic fair once, and apologized. When she asked why, I said,“Well, since have more gritation pull on you at this moment then any of the stars or planets, I probably threw that horoscope reading for that man all out of wack! Would you like me to ask everyone to leave the fairgrounds so that this could be done more accurately?”
Y’know, psychics got no sense of humor.
That was supposed to be “gravitation”, y’know!
[long story] My wife and I went to a live action role-playing game one time, as staff (NPCs) and she was playing an old gypsy woman. The game was a very complex one, a background mythology (totally ficticious). My wife made up some “bones” (wooden model of dinosaur skeleton) and wrote the symbols of the different gods on them. Then, she’d tell fortunes by tossing the bones, and reading what was up, what was down, what was on top, far away, etc. So we had made up some banter – she’d point to how the symbol for luck and the symbol for travel were intertwined, meaning the person was going to take a journey and would have bad luck. That kind of fun stuff.
An amazing number of players later came to her and told her that her predictions were RIGHT on target. Many of them thought that, as staff, she had inside information (which was not the case.)
The power of believing, I guess. [/long story]
One night, a friend of mine made up his own method of divination. We were sitting at an all-night restaurant, when he started telling us about “Lactomency”, or divining the future from reading milk drops. He then took a little cream canister, and proceded to tell us all our futures.
“The large print givith, and the small print taketh away.”
Tom Waites, “Step Right Up”
jab1 wrote:
They are? I was aware that some people don’t know what “inflammable” means, but I’ve never heard of anyone thinking that “flammable” means its opposite.
I didn’t have time yet to check out the Astrology Defense Kit, but here is another article on the topic, originally by the North Texas Skeptics: http://www.reall.org/newsletter/v05/n03/astrology.html
tdn (woo hoo! Another newbie to sacrifice to Cthulu!) wrote:
My understanding is that Astrologers need to know your rising sign in order to cast horoscopes properly. Your rising sign is the Zodiac constellation that’s juuuuuuuust rising over the Eastern horizon at the moment you were born.
Such information could be calculated by knowing the time of day when you were born, but as you’ve indicated, you would also have to know the longitude your birth took place at (just knowing the time zone would not give enough precision). 'Way back when Astrology was invented, the ancients were not aware that the Earth was curved and that a different constellations would therefore be on the horizon as seen from different points on the Earth – perhaps your “rising sign” is really supposed to be the sign rising on the Eastern horizon as seen from the city of Babylon at the instant you were born.
I was born on July 17, 1965, at 5:30 AM central daylight time, in St. Paul, Minnesota. Anybody wanna compute my rising sign?
Well, astrologically, I wouldn’t know, but based on your age and sex, I would guess that it would be a tented blanket.
Tom~
—Yawn—
All this talk of astrology is boring. I think I’ll just trust my future to God and go to bed.
The trouble with Sir Launcelot is by the time he comes riding up, you’ve already married King Arthur.
tomndebb: D’OH!
jab1 wrote:
I hadn’t heard about the “vice versa” part. Way back in my undergrad days, I learned in my Early History of Science class that the “Astronomy” curriculum of the Medieval University Quadrivium consisted of both of what are now called astronomy and astrology. I’ve also read in James Randi’s The Mask of Nostradamus that one of the first English translations of the Centuries starts by calling Nostradamus “one of the greatest astronomers that ever were.” But I’ve never heard of the science of mapping the stars or calculating the positions of the planets being called “astrology.”
The truth, as always, is more complicated than that.