HOW YOU CAN CALCULATE THE RISING SIGN
Often can arise the curiosity to know how to calculate the ascendant, looking on the internet there are several sites that explain how to do it but for one reason or another I have not found any site that explains it in full details and so I decided to write this little tutorial using same case explained step by step.
THE SIDERAL TIME
The purpose of ascendant calculation it's to find the 'Sidereal Time' of the own birth, the sidereal time or 'stars's time' is defined as the time the earth needs to make one complete rotation around the stars and so it's useful to determine where are the stars in a given time, so knowing this figure at the time of the birth of a person it's possible 'to see' which are the rising costellation at east. For further information about sideral time you can look at:
BASIC INFORMATION TO COMPUTE THE RISING SIGN
We can start doing the 'shopping list', in other words look at which are the data we need to cumpute the ascendant calculation, do not be afraid because we will see together how to find most of the necessary informations:
1) Exact time of birth
2) There was summer time?
3) Latitude and longitude of the place of birth
4) The Time Zone
5) The tables with the constellations positions or 'houses table'
Ok! Let's start with an analysis of those data:
1) the exact time of birth is crucial for a correct calculation of ascendandt, the best way to know would be to ask the parents the exact time of birth but this is not always possible, so we can use the one on birth certificate but often it is not completely accurate because it refers to the time written by the doctor and it can be rounded... but we be satisfied
2) the information about summer time must be considered because it moves the time of one hour and you can undestand that this is essential to calculate the ascendant... for my site I build an archive of all summer time for the past years but each country has its history so I had to delegate to you to find this information on internet if you are not birth in Italy... I'm sorry
3) the latitude and longitude of a place are the coordinates to locate its position on the Earth's sphere, I think that the best way to understand these two quantities is to observe this picture:
we need to know latitude and longitude for our calculation because the appearance of the sky changes moving from one point to another and from one hemisphere of the globe to the opposite.
Today know the latitude and longitude of a place is much easier than in the past ... and we have several options:
-use gps antennas, the ones used for navigation systems ... often the navigation software has the ability to display latitude and longitude of the current position
a small window with the valuable information of latitude and longitude will appear.
-use sites that use google maps and automate the research for latitude and longitude as example the excellent:
-use data available on-line. For my site I have gathered the full details of all the Italian country and the coordinates of the major city in the world ... excellent starting points if you decide to follow this way are these sites:
4) The tables with the astral informations which we'll used are referred to Greenwich so we need to solve the question 'what time it was in Greenwich when I was born?' We therefore need to know our timezone... very useful is the image hosted on the pages of wikipedia about time zones:
for my site I had to build a database with the timezone of the main cities of the world, even here in web fortunately there is help ... I can suggest you these links:
one last thing about latitude and longitude remember that these quantities are expressed in degrees and minutes (sixtieth of a degree) we'll re-find this information below
5) Once we have reported ideally at the Greenwich meridian at the time of our birth, we can finally see the sky on the horizon and look at the emerging constellation to the east, this is a very poetic way but it is not the most comfortable, fortunately we are in aid the tables that contain this information... in the literature there are many books devoted to this purpose but, once again, we have the internet as an alternative solution, as example on this site you can find these tables that,obviously, depend on latitude:
you can see that the tables are shown only for latitudes greater than zero and thus for the north hemisphere, if we want to calculate the ascendant for someone born in the sud hemisphere it's enough to consider the table associated with the latitude without the minus sign and the reverse the results.
For my site, of course, I had to store all those informations.
Now that we know something more about ascendant we can move on to real calculation... without wasting time let's start with an example step by step and let's analyze the details of the calculation.
A) EXAMPLE OF CALCULATION OF RISING SIGN FOR HEMISPHERE NORTH - LONGITUDE EAST
Calculation of ascendant for Stefano born in Rome on 01/07/1975 at 11.37am
- As first step we convert the time of birth in minutes from previous midnight, in our example 11.37am means that Stefano was born 11 * 60 +37 = 697 minutes after midnight, this will be our starting value for the calculation sidereal time of birth:
SIDERAL TIME = 697
- on first July 1975 there was summer time so subtract 60 minutes:
SIDERAL TIME = 697-60=637
- move ideally on Greenwich's meridian, Rome is one hour ahead of this one so still subtract 60 minutes:
SIDERAL TIME = 637-60=577
- tables that we are going to consult to find the ascendant, refer to midnight but Mr. Stefano was born at 11.37am ... and so? Small error but we are fussy and want to make a precise calculation and then let's make a correction due to the time elapsed since midnight, as we see:
a calendar year, from the viewpoint of the sidereal time, is divided into 24 hours which means that each day corresponds about 24 * 60/365 = 3.94520547945 minutes and then try to spread these minutes in a single day and see how much correction should be made for Stefano ... it just a simple proportion:
1440:3.94520547945 = 697: x
where 1440 are the minutes in a day (24 * 60) while 697 are the minutes between midnight at the time of the birth of Stefano (the first value we have calculated)
let's solve our proportion and see that x is:
x = (3.94520547945 * 697) / 1440 = 1.90958904
we can approximate our value to 2 minutes and then we can update our sidereal time:
SIDERAL TIME = 577+2=579
- now we calculate the sidereal time since the beginning of year, the reason because we do it, it's the same we see onin the previous paragraph with the difference that this time we have to do the calculation related to a year and not to a day, remake the reasoning: a calendar year, from the viewpoint of the sidereal time is divided into 24 hours which means that each day corresponds about to 24 * 60/365 = 3.94520547945 minutes, Stefano was born on July 1, and so the days since the beginning of year are 181. Looking at the sideral time table we look that the sidereal time of the first in January is 6 hours and 36 minutes and so to calculate the sidereal time that we are interested we can do this calculation: 396 +181 * 3.94520547945 = 1110.082
where 396 are the 6 hours and 36 minutes of the first of January converted to minutes (6 * 60 +36) in this case we can make a small approximation ... then we can update our sidereal time:
SIDERAL TIME = 579+1110=1689
- Now consider the correction due to longitude of a place on birth. Longitude on each point on the Earth is conventionally included in the range -180, +180 which means that we can consider the Earth's surface divided into 360 degree ... walking ideally along this surface we get a tour that takes us to complete 24 hours of travel ... which means that each time we move a degree we have a fix of (24 * 60)/360= 4 minutes.
Stefano was born in Rome, which has longitude 12:29 EAST and latitude 41.54 NORTH; moving towards east time grows, then increase the time considering a correction factor: (need to emphasize a fact, the coordinates are expressed sixtieth of a degree so in order to calculate we could transform the sixtieth in cents but the error is minimal and acceptable for our purposes)
SIDERAL TIME = 1689+4*12.29=1738.16=1738
- As I already told at the beginning, tables of the houses are generally reported for the northern hemisphere so if our latitude is below the equator we need to make a correction of 12 hours, but is not the case of Mr. Stefano
- At this point we have our data that we can use on the tables to reveal our ascendant, but I should emphasize a few things:
1738 minutes are more than the minutes in a day which are 1440 (60 * 24) so we have to make a 'module 1440' operation in our case this means simply subtract 1440 minutes:
SIDERAL TIME = 1738-1440=298
transform our sidel time in hours and minutes:
SIDERAL TIME = 4h58m
let's get the tables that are closest to our latitude of birth, in the case of Stefano this one is 41.54N therefore we can take the tables for latitude 40 degrees north, then let's scroll the data until we find the line that interests us:
- we can stop at the line 04h56m and then we can read in the data column ASCEND the desidered value:
which means that Stefano has a rising sign in Virgo (Virgin) positioned at 17°14'
B) EXAMPLE OF CALCULATION OF RISING SIGN FOR HEMISPHERE SOUTH - LONGITUDE WEST
Let's analize now an 'opposed' case respect to the first, look how calculate the ascnedant for a person born at east of Greenwich and in the south emisphere. We'll calculate the ascendant of Lorenzo born in Lima (Peru) Long 77 WEST Lat 12 SOUTH at 5 February 1990 at 23:47
this time we can go faster:
- Convert in minutes the birth time:
- On 5 February 1990 there was no daylight saving on Lima so adjustments are not necessary
- move ideally to Greenwich's meridian, Lima is 5 hours behind this one so add 60 * 5 = 300 minutes:
SIDERAL TIME = 1427+300=1727
- perform the correction due to the fact that Lorenzo was born more near 6th of February then 5th, so set our proportion:
1440:3.94520547945 = 1427: x
x = (3.94520547945 * 1427) / 1440 = 3.909589 = approximately 4 minutes
- calculate the sidereal time, Lorenzo was born on 5 of February so 35 days have passed since the beginning of the year.. do our calculation:
3.94520547945 * 396 +35 = 534.82 = 534
- perform the correction due to the longitude, Lima has longitude 77 west and then we subtract this correction factor:
SIDERAL TIME = 2265-4*77=1957
- now we must be careful because Lima is in the southern hemisphere, indeed its latitude is 12 south and then the sky is 'reversed' ... so to solve the things we are going to add 12 hours to our calculation:
SIDERAL TIME = 1957+(12*60)=2677
- let's do the 'module 1440' operation and we obtain our final value:
SIDERAL TIME Mod 1440 = 2677 Mod 1440= 1237 =20h37m
remember that Lima has latitude 12 south and then we can use, with good approximation, the tables of the houses on the latitude 10 North, so take the section that join our data:
- read the value in the column ASCEND and get 14TA23 ... then it would seem that the ascendant is 14°23' Taurus ... but remember that we used the emisphere's nord tables so we need a final correction, we have to 'mirror' the zodiac sign and take the opposite of what it's found, then the acendant will not be 14TA23 but 14SC23 Scorpio 14°23', so finally Lorenzo know his Rising Sign