Skyscript Astrology Forum

Using a geocentric view, the Sun is seen to travel through the all the zodiac signs once a day, right? My question is, does the Sun take the same amount of time to pass through all 30 degrees of each sign?

If it does, then it would take exactly 2 hours per sign. If it doesn't, where can I find the exact numbers?


My reason for asking is because the ascensional times of the signs are different, so I have a feeling that the Sun travels more quickly in some signs, and more slowly in others.


EDIT: Edited the title.

Your question betrays some confusion. The Sun does not travel through all the signs of the zodiac once a day; it travels about 1 degree (sometimes a little more, sometimes a little less, averaging 0?59'08"/day) by its own motion. The entire celestial sphere (including the Sun and other planets, as well as the zodiac itself) revolves around the earth once in a day -- from a geocentric perspective.

The ascensional times of the signs vary according to their relationship to the equator and to geographical latitude. The proper motion of the Sun through the zodiac varies according to the seasons.

Larxene wrote:Using a geocentric view, the Sun is seen to travel through the all the zodiac signs once a day, right? My question is, does the Sun take the same amount of time to pass through all 30 degrees of each sign?

If it does, then it would take exactly 2 hours per sign. If it doesn't, where can I find the exact numbers?


My reason for asking is because the ascensional times of the signs are different, so I have a feeling that the Sun travels more quickly in some signs, and more slowly in others.

Do you mean once a year? The sun has an average motion of about 59' 08 a day, but can be a bit slower or faster through the year. In particular due to the slight eliptical orbit of the earth around the sun, the Sun appears, from a geocentric view, to speed up a bit through the (northern hemisphere) winter months and slower during summer. This is because due to the eliptical orbit, the earth is slightly closer to the sun in January than it is in July.

Obviously the sun doesn't move two hours per sign but instead moves roughly one month per sign.

Instead you might be confusing this for the ascendant (I'm trying to follow what you mean) as the ascendant point would pass through the entire zodiac in a day. That is, on average, about 2 hours a sign. However, some signs rise quicker or slower depending on your latitude. Traditionally these were signs of short or long ascension, called crooked and straight respectively (in the northen hemisphere). In the northern hemisphere, the crooked signs rise quickly, and these are the 'northen' signs which are from capricorn to gemini. They are referred to as crooked as they rise obliquely.

I'm not sure what exactly you had in mind in your original question, but hopefully some of this helps answer it for you.

Hello Martin and Paul,

*bangs head on the wall* Yeah, I confused the Sun's movement through the zodiac with the Ascendant's somehow. I meant to ask about the Ascendant's movement throughout the zodiac.

I may still have some more questions about the Ascendant's movement throughout the zodiac...for that, I edited the topic title so that it stays relevant.

I think I conflated the Sun and Ascendant because the Sun rises in the east, and the Ascendant also "rises" on the east...

Everything rises in the east, because the earth rotates from west to east, making it appear that the celestial sphere rotates around us from east to west. The movement of the ascendant through the zodiac is really the movement of the zodiac across the eastern horizon. Keeping that in mind may make it easier to visualize.

The earth turns on its axis, which is at right angles to the equator. Therefore, from a geocentric perspective, the celestial equator turns around us in the sky, rising due east and setting due west. But because the zodiac is skewed with respect to the equator (this is known as the obliquity of the ecliptic), different signs and degrees of the zodiac rise at different points and also take different amounts of time to rise and set. (Those that rise slowly set quickly, and vice versa.)

Hey Larxene, yeah it would intuitively seem like each sign should rise (i.e. cross the eastern horizon) in the same amount of time but it?s not so. Imagine you?re standing on the equator, facing east. The whole sky is rotating around the Earth, so a constant number of degrees pass up and over the eastern horizon each minute. If the ecliptic perfectly overlapped the celestial equator, each sign would rise in the same amount of time (1/12th of a day). But the ecliptic is tilted by 23.5 degrees relative to the celestial equator. So different signs are tilted differently relative to the horizon. Equinoctial signs are very tilted relative to the horizon. Thus, less sky-distance is needed for them to completely clear the horizon. They completely rise relatively quickly. The solstitial signs are more vertically oriented, or perpendicular, relative to the horizon. So more rotation of the sky is needed to get them across. This takes relatively longer.

Note that at the equator, objects in the sky rise straight up from the horizon, and this creates a symmetry about the equinoxes, and also the solstices. Signs before and after each equinox rise (clear the horizon) fastest; signs before and after the solstices rise slowest. But north of the equator, the sky doesn?t appear to rise vertically ? it rises obliquely to the south (think of the path of the sun, if you live in the northern hemisphere). This distorts the above described motion relationship of the signs to the horizon and breaks the symmetry about the solstices. It?s a little tough to explain without pictures, but the signs before and after the spring equinox clear the horizon (rise) fastest, and the two signs before and after them (e.g. Aquarius/Taurus, then Capricorn/Gemini, etc.) progressively take longer and longer to rise, up till the two signs about the autumnal equinox, which take the longest.

As noted at http://en.wikipedia.org/wiki/Ascendant,

?At the latitude of St. Petersburg, Russia:
Pisces and Aries ascend in only thirty minutes
Aquarius and Taurus ascend in only forty-five minutes
Capricorn and Gemini ascend in an hour and a half
Sagittarius and Cancer ascend in two hours and forty minutes
Leo, Virgo, Libra and Scorpio take as much as three hours and fifteen minutes to ascend.?

(I edited the above just slightly.)

The signs that take longer are called signs of long ascension; those that take shorter, short ascension. Other descriptions include crooked and straight signs.

The Babylonians were aware of the above variations of rising time, but didn?t possess spherical trigonometry. So they set the shortest times, the 30 degree segments before and after the spring equinox (equivalent to modern Pisces and Aries), at 20 degrees of rising time, and then progressively added 4 degrees to the 30 degree segments preceding and following (so the areas equivalent to modern Aquarius and Taurus would have 24 degrees, Capricorn and Gemini 28, etc.). This was known as System A. Another Babylonian reckoning, called System B, started with 21 degrees of rising time and added 3 degrees going each way. If you add all the degrees up in either system, however, you get 360. (The above comes from Rob Hand?s ?On the Invariance of the Tropical Zodiac?.)

So, there you have it.

-Phil

@Martin and Phil,

I was trying to imagine the movement of the stars in the sky viewed from Earth, and also why the zodiac signs take a different amount of time to rise. I have read Wikipedia's entry on the Ascendant.

Thanks for the information!

Larxene, I am banging my head against a wall now (well, not literally) because this was a big issue in Antiquity. The ancient Hellenistic astronomer/astrologers knew that length of times varied between, say, Alexandria and Rome; and then they worked out the math to account for it; building (I think) on Babylonian arithmetic. I just can't recall who did it. I want to suggest the Almagest, but it might not be there.

It raises some interesting questions about degrees vs. representations of time in the horoscope in the whole signs house system.

Anybody?

Waybread writes:

The ancient Hellenistic astronomer/astrologers knew that length of times varied between, say, Alexandria and Rome; and then they worked out the math to account for it; building (I think) on Babylonian arithmetic. I just can't recall who did it. I want to suggest the Almagest, but it might not be there.

I think Hipparchus was possibly the first to suggest this approach. However, Ptolemy seems to be our oldest surviving source who sets out this information in a sophisticated astronomical way for locations across the earth.

Ptolemy set out this information in his Handy Tables, which tabulated all the data needed to compute the positions of the Sun, Moon and planets, the rising and setting of the stars, and eclipses of the Sun and Moon in the various Klimata. Ptolemy's Handy Tables provided the model for later astronomical tables or z?jes. In the Phases of the Fixed Stars Ptolemy gave a parapegma, a star calendar or almanac, based on the rising and setting of stars over the course of the solar year provided for each Klima.

Ptolemy's provision of this astronomical information based on Klimata ties into his knowledge of geography. While we tend to think of Ptolemy as an astronomer and astrologer he was also one of the greatest geographers of the ancient world. Hence following a geographical technique the world is divided in numerous Klimata based on latitude from the equator:

http://en.wikipedia.org/wiki/Clime

It raises some interesting questions about degrees vs. representations of time in the horoscope in the whole signs house system.

Anybody?

A fascinating question! I have been using whole sign houses for a few years myself but I have pondered this question. It seems that as astrologers we sometimes prefer the symbolic over the literal/astronomical.

For example we mostly use zodiacal over mundane aspects. In this instance we seem to be prefer a symbolic, idealized approach over a more astronomically literal approach based on geographical location. Why?

Looking at the calculation of houses there seem to be a similar choice between the more literal/localised and idealized/symbolic approaches.

Undoubtably, most astrologers are taught the view that the different rising times of signs at the ASC justify a quadrant approach.

However, I think the ancients probably had a fundamentally different logic in mind in assigning 30 equal degrees to each sign in whole sign houses. It is clear they were perfectly well aware that the ascensional rising times of signs varied depending on location.

My speculation is that they were probably thinking of the solar cycle based on the Sun spending 30 degrees each year in each sign. From this solar perspective the signs are equal though the day/night times vary depending on season.

For a tropical zodiac derived from the movement of the Sun this has some logic.

Arguably, equal house cusps derive from a similar solar logic with their use of exactly 30 degrees per house. The Vehlow-Raman Equal house system seems to pick up the solar cycle in an even stronger way than the more usual equal house system. As in standard equal houses each house is 30 degrees but in this system each cusp sits in the middle of the house. The solar logic here in relation to the ascendant is that the Sun has a traditional orb of 15 degrees. So if one imagines the Sun rising on the ASC its influence extends 15 degrees in each direction from the ASC degree.

I am going to have to drop out of the forum for a while but I will look forward to checking out this thread when I get back next week.


Mark

Really helpful, Mark. Also your post on the other thread about time conventions.

Mark wrote:
For example we mostly use zodiacal over mundane aspects. In this instance we seem to be prefer a symbolic, idealized approach over a more astronomically literal approach based on geographical location. Why?

Mark

mark, this is a great question that mystifies me as well.. i like the feature in solar fire where you can transform a chart to show you what the chart would look like using diurnal arc as opposed to zodiac positions. for anyone interested, go to harmonic/transform then choose z-analogue diurnal arc..