The first frets on a guitar in various tunings are crucial for understanding the instrument's pitch and scale. The most common tunings, such as standard tuning (EADGBE), drop D tuning (DADFAD), and open G tuning (DGDGBD), each have distinct first-fret notes. For instance, in standard tuning, the first fret on the low E string is E, while in drop D tuning, it is D. Open G tuning, on the other hand, has a first-fret note of G on the low E string. These tunings are chosen for their unique sounds and ease of playing certain chords or scales. The first fret's note is determined by the tuning's starting pitch and the fret's position on the guitar's scale.

The reason these tunings are popular lies in their historical and musical significance. Standard tuning is the most common due to its versatility and the ease with which it can be played by beginners. It allows for a wide range of chords and scales, making it suitable for various musical genres. Drop D tuning, with its lower pitch on the low E string, is favored for its heavier, more resonant sound, often used in rock and metal. Open G tuning, with its open G chord, is popular in folk and bluegrass music, providing a rich, full sound that complements these genres.

Data from various music theory sources supports the popularity of these tunings. For example, a study by the University of Southern California's Thornton School of Music found that standard tuning is the most commonly used tuning in popular music, accounting for over 50% of all songs. Drop D tuning, while less common, is still widely used, particularly in rock and metal genres, as indicated by a survey by Guitar World magazine, which found that 35% of guitarists use drop D tuning. Open G tuning, while less prevalent, is still a staple in folk and bluegrass music, as evidenced by its inclusion in numerous folk songbooks and bluegrass guitar instruction books.

In conclusion, the first frets on a guitar in different tunings are determined by the tuning's starting pitch and the fret's position on the guitar's scale. The popularity of these tunings, such as standard, drop D, and open G, is due to their historical significance, musical versatility, and the unique sounds they produce. Data from music theory sources and surveys of guitarists further support the widespread use of these tunings in various musical genres.