The number that goes unreported
Every page about this date will give you the sign. Leo runs from the second half of July to about the twenty second of August, and the tenth sits well inside it, nowhere near either end. There is no doubt to resolve here and no boundary to worry about.
The useful figure is the longitude. The Sun covers a little under one degree a day, so each date in the year owns a narrow slice of its sign, and this one owns the stretch just past seventeen degrees. The window across the last century is only about one and a half degrees wide, and it stays that tight because the leap day resets the calendar against the orbit every four years before any drift can build up.
Where seventeen degrees falls inside the sign
Each sign divides into three bands of ten degrees, an inheritance from Egyptian star clocks that later writers fitted with planetary rulers. Seventeen degrees sits in the middle band of Leo, the stretch from ten to twenty, and that band answers to Jupiter.
Leo happens to be one of the places where the two surviving rulership schemes agree. The Chaldean count, which runs the planets in order of apparent speed from the first degree of Aries onward, arrives at Jupiter here. The triplicity scheme, which hands a sign's bands to the rulers of the fire signs in zodiacal order, arrives at Jupiter as well by way of Sagittarius. Elsewhere a reader has to pick between two confident answers. On this band there is nothing to pick between.
What the tradition reads into the band
Leo is fixed fire under the Sun, and the older texts describe the sign in terms of display, authority and a settled centre of gravity. That description covers a full month of birthdays and does not distinguish between any of them.
The middle band adds the Jupiter colouring. The tradition reads these degrees as the generous and expansive stretch of Leo, warmer in manner than the opening degrees and less combative than the closing ones. That is an interpretation carried down in the literature, not a measurement, and it is worth holding at that distance. A calendar date confers no temperament on anyone.
It is also worth noting what the band does not do. It does not replace the sign, it does not compete with it, and it does not add a second sign to the reading. Thirty degrees of Leo are divided into three, and the division tells you which third a position occupies. Anyone offered a decan as though it were a hidden extra sign has been sold something the scheme never contained.
What the calendar cannot reach
The Sun is the only body a date pins down. The Moon travels between twelve and fifteen degrees in a day, so it can occupy two signs across a single tenth of August, and a birth in the morning may not match one at night.
The rising sign is wider open still. It turns through all twelve signs as the Earth rotates, changing every couple of hours or so and shifting with the latitude of the birthplace, so the date narrows it down not at all. The widget above takes your year, hour and place, returns an exact solar degree instead of a range, reports how far that degree sat from the nearest sign boundary, and works out the placements a calendar has no way of supplying. The sun sign is the least personal thing in a chart, and on a date like this one it is also the least informative.
Questions people ask about this
Is 10 August always Leo?
Yes. The Sun enters Leo around the twenty second or twenty third of July and does not leave until roughly the twenty second of August, so this date has never fallen outside the sign in any modern year. No birth time is needed to establish that much.
What degree of Leo is a 10 August birthday?
Somewhere between about sixteen point nine and eighteen point three degrees, taking noon across the last century. Your own figure depends on the year, the hour and the time zone of the birthplace.
Which decan does the date fall in?
The second, which covers ten to twenty degrees of Leo. The whole range for this date sits inside it, so the band does not change from year to year.
Who rules that band?
Jupiter, under both of the schemes still in common use. The Chaldean order reaches Jupiter by planetary speed and the triplicity scheme reaches it through Sagittarius, which is unusual agreement between two systems that often part company.
Does the birth year change anything?
Only slightly. Leap years pull the position back and the three years after each one push it forward again, which is what produces the small spread. The sign and the band survive that movement untouched.
Why do I still need my birth time?
Because the Moon and the rising sign are not fixed by the date at all. The Moon can change sign during the day and the Ascendant moves through the entire zodiac in twenty four hours.