This is a misunderstanding of astrology. Astrological signs are not the same as constellations, even though they are named the same as or similar than twelve of the thirteen constellations which cross the ecliptic.
Astrological signs are measurement of ecliptic longitude, each one thirty degrees, starting with Aries. There are two intersection points between ecliptic and equator, so one of them will be called zero; specifically, it is the spring equinox in the north hemisphere. You will then usually specify the degrees past the sign, e.g. "0 Aries" is 0 degrees, and "3 Cancer" is 93 degrees.
"Tropic of Cancer" and "Tropic of Capricorn" are not having to do with constellations; they have to do with the astrological signs of those names. When the ecliptic longitude of the Sun is at 0 Cancer then the Sun is over the Tropic of Cancer.
(This assumes you are using the "tropical zodiac" which is based on the equinox of date. If you are using a "sidereal zodiac" with a specific ayanamsha (the word "ayanamsha" is a Sanskrit word denoting the amount of precession of equinoxes) then it is instead relative to a specific angle at a specific date.)
So, their signs are not wrong, although you still cannot predict facts about people's lives and other stuff like most astrologers try to do, by the use of the astrological signs, and using the correct ones is no better than using the wrong ones. There are good arguments that can be made against astrology, but "the signs are all wrong" is not a valid one.
Astrology does get the positions of objects correct as astronomy does, although to understand them you would have to understand the conventions in use, which are different than the conventions commonly used in modern astronomy.
The dates commonly given for Sun signs in newspapers are approximately correct but are not exact. The exact dates (and times of day; not only the date) varies by year, and this is related to the reason why we have leap years.
I'm not sure how the Tropics of Cancer/Capricorn got in this discussion, they are latitudes of the earth. I know nothing about astrology, but according to the article I posted your sign is the constellation the sun was "in" when you were born. I'm not clear how one would determine astronomically what sign the sun is in, given that the stars aren't visible when the sun is and it cross half the sky. Maybe it's the constellation just before sun up or just after sun down? Anyway, the earth's axis certainly precesses, so if you just take some ancient astrological information and apply it to modern dating, you're going to get the wrong sign.
> I'm not sure how the Tropics of Cancer/Capricorn got in this discussion, they are latitudes of the earth.
They are latitudes of the Earth (although the obliquity of the ecliptic can change over time, so they are not always the same latitudes of the Earth). Specifically, they are the latitudes of the Earth that the Sun will be directly above if the ecliptic longitude of the Sun is 0 Cancer and 0 Capricorn (when the Sun is at 0 Aries and 0 Libra, it is directly above the equator).
> your sign is the constellation the sun was "in" when you were born
It is not. "Your sign" usually means your Sun sign (at the time you were born; this can be any time of day or night), and it is not the same as a constellation, even if it has the same name as that sign. If your Sun sign is Aries, that means that the ecliptic longitude of the Sun at the time you were born was greater than or equal to zero degrees and less than thirty degrees, counting from the spring equinox as zero. That is what it means. It does not have to do with the constellation named Aries, although people who are not familiar with astrology often confuse it with that.
Astrological signs are a measurement of ecliptic longitude. One sign = 30 degrees, therefore 12 signs = 360 degrees.
You can also determine the sign of the Moon and planets, which would be their ecliptic longitude, like you would with the Sun. For example, if Moon is in the sign Libra then the ecliptic longitude of the Moon is greater than or equal to 180 degrees and less than 210 degrees. Libra is the opposite direction from Aries, so if Sun is Aries during a full moon, then the Moon will be Libra, since the opposite directions are 180 degrees apart. This is not having to do with the constellations named Aries and Libra, which is different.
> If you were born between March 21 and April 19, your astrological sign is said to be Aries. But this was only true for a while, back when the system was set up in 600 BC.
Actually, it is still approximately true, although the equinox does not occur exactly on March 21 every year. The beginning of the astrological sign Aries is at the time when the equinox does occur, which is not always the same time of day.
> From March 11 to April 18, the Sun is actually in the constellation of Pisces!
This is irrelevant. The Sun may be in that constellation, but the constellation of Pisces is not the same as the astrological sign named Pisces. Astrological signs are a measurement of ecliptic longitude.
> The science behind astrology may have its roots in astronomy but don't confuse these two disciplines.
This is correct, but it does not mean that astrologers use an incorrect position of the Sun.
> The ecliptic, or the path of the sun as it's perceived from the revolving Earth, passes through the constellations that formed the Zodiac: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. Astrologers skip a 13th constellation that also resides on the ecliptic: Ophiuchus.
Again, astrological signs are not the same as constellations. (Also, there are no constellations named "Scorpio" and "Capricorn"; their names are "Scorpius" and "Capricornus".) Astrologers do not "skip" Ophiuchus; but there is not an astrological sign by that name.
There are good mathematical reasons to have twelve astrological signs and not thirteen. They named them after twelve of the thirteen constellations which cross the ecliptic (there are also constellations which do not cross the ecliptic), but astrological signs are not and never were the same things as constellations; they are a unit of measurement of ecliptic longitude.
> Ancient astrologers grouped the 12 signs according to the classical elements.
Yes, and modern astrologers still do. Additionally, there are also the three modes (cardinal, fixed, mutable). Together, these are like a residue number system, but with elements/modes instead of numbers.
> The first day of spring in the Northern Hemisphere was once marked by the zero point of the Zodiac.
It still is, if you are using the equinox of date (which is common; it isn't wrong, although it is not the only way to do it). The first astrological sign is named "Aries", therefore the zero point is called "0 Aries" (like how the first day of the year is called "January 1", because the first month is called "January").
> The constellation Aries encompassed the first 30 degrees of the ecliptic; from 30 to 60 degrees was Taurus; from 60 to 90 degrees was Gemini; and so on for all 12 constellations of the Zodiac.
This was never true; they were never all encompassing exactly thirty degrees of the ecliptic. Astrological signs did and still do.
They also link to Astrodienst. At the time I am writing this, the Sun's ecliptic longitude is 20 Leo 50'21". This is the same as 140 degrees, and fifty arcminutes and twenty-one arcseconds.
Astrological signs are measurement of ecliptic longitude, each one thirty degrees, starting with Aries. There are two intersection points between ecliptic and equator, so one of them will be called zero; specifically, it is the spring equinox in the north hemisphere. You will then usually specify the degrees past the sign, e.g. "0 Aries" is 0 degrees, and "3 Cancer" is 93 degrees.
"Tropic of Cancer" and "Tropic of Capricorn" are not having to do with constellations; they have to do with the astrological signs of those names. When the ecliptic longitude of the Sun is at 0 Cancer then the Sun is over the Tropic of Cancer.
(This assumes you are using the "tropical zodiac" which is based on the equinox of date. If you are using a "sidereal zodiac" with a specific ayanamsha (the word "ayanamsha" is a Sanskrit word denoting the amount of precession of equinoxes) then it is instead relative to a specific angle at a specific date.)
So, their signs are not wrong, although you still cannot predict facts about people's lives and other stuff like most astrologers try to do, by the use of the astrological signs, and using the correct ones is no better than using the wrong ones. There are good arguments that can be made against astrology, but "the signs are all wrong" is not a valid one.
Astrology does get the positions of objects correct as astronomy does, although to understand them you would have to understand the conventions in use, which are different than the conventions commonly used in modern astronomy.
The dates commonly given for Sun signs in newspapers are approximately correct but are not exact. The exact dates (and times of day; not only the date) varies by year, and this is related to the reason why we have leap years.