Which star is the brightest in the Lyra constellation?

The brightest star in the Lyra constellation is Vega. It holds the distinction of being one of the most luminous stars in the night sky and is part of the Summer Triangle asterism, which includes two other bright stars from the constellations Aquila and Cygnus. Vega is notable for its relative proximity to Earth, at about 25 light-years away, and because of its brightness, it has been historically used as a standard in photometry.

In terms of its characteristics, Vega is a main-sequence star of spectral type A0V, indicating it is hotter and more massive than the Sun. This contributes to its high luminosity. The star's brightness also makes it an essential point of reference in astronomy for calibrating other stars' brightness and for various other measurements.

While Altair and Deneb are also bright stars in their respective constellations, they do not belong to Lyra. Regulus, found in Leo, is another bright star but is not part of the Lyra constellation as well. Thus, Vega is unequivocally the correct answer in this context, providing not only brilliance but also a key role in celestial navigation and astronomical studies.