What does “closest” mean?
We are describing the Star of Your Birth as the star that was aligned with the sun on the day you were born, or other important date. We are using stars bright enough to be seen in a reasonably dark sky, magnitude 4.8 or greater. Since the position of the sun each day is described by its right ascension (RA), “aligned” is going to mean a star with an RA that most closely matches the sun’s RA at some time during that day.
“Closest” also means that the star is in the Zodiac, a band of sky on either side of the ecliptic where the planets are observed to pass through. There will be just a few exceptions to this at times where there are no bright stars in that section of the zodiac.
We realize that this can seem complicated. Unfortunately, nature did not give us a simple system. We do not want to introduce inaccuracies by over-simplifying this. Please feel free to contact us via the form and we will be glad to help.
Choosing Your Star
The sun covers 3.5 to 4.25 minutes of RA each day. The stars are scattered randomly, so on any given day there may be one, several, or no bright stars in that segment of sky. There are many factors affecting which stars might be near the sun on a given day.
This causes the largest variations year-to-year. Is your date in a leap year, or 1, 2, or 3 years after? We will call this L, L+1, L+2, and L+3. Note that the leap year effect does not start until Feb 29th of the year and continues until Feb 28th of the following year. For example, 1960 was a leap year, but if your date is January 15th of that year, the effect hasn’t kicked in yet, so you are really L+3. If your date is January 15 of 1961, the effect is still occurring and for this purpose you are L. The leap year cycle has the biggest effect on accuracy. You should know if your date of interest is in a Leap, Leap+1, Leap+2, or Leap+3 year.
So, if your date of interest is January 1-February 28, do not think whether your year is a leap year, L+1, etc., instead think of what was the year before. If the last 2 digits of your year are divisible by 4, then it is a leap year. Century years must be divisible by 400. 2000 was a leap year, but not 1900 or 2100.
This causes the values of RA to change, because this effect causes the zero point of RA to move. So it is corrected every 50 years. Most popular planetarium programs can show you a yearly correction. We have analyzed sun and star positions for 1950 and 2000. If there is a change, you can estimate that it happened in 1975.
Time of Day and Time Zone
If there are several stars in the same day, the sun will pass each one at different times. Also, at any one instant, the sun is at a certain position. But people in San Francisco, Cleveland, Boston, Paris, and Moscow will all be having a different time at that instant. We have determined sun positions for Greenwich, England at 0 Longitude, the standard for astronomy. If you live more than 8 time zones away (your time zone is GMT+8 or -8), or if you are interested in a time very late or early in the day, and you want very accurate results, consult the day before or after your date for a star.
Our Charts and Suggestions
For each day, the suggestions we give will be a star very close to being aligned with the sun for that day. The star descriptions have the birthdays from Jack’s original research. He only looked at 1950 data and did not know about the leap year effect. (Kevin didn’t either, until he did some computer-aided analysis.) In most cases Jack’s suggestions will be appropriate. Most differences will be in L+2 and L+3 years.
If you are really a stickler for accuracy and want the most accurate result, send a comment with the date, year, time zone, and time of day. Kevin will look at it for you and respond to the email you leave with the comment. The comment will not be published but will be read and responded to in a reasonable time.