A planet transits an 11 ^ { th } magnitude , G1V star in the constellation Corona Borealis .
We designate the planet XO-1b , and the star , XO-1 , also known as GSC 02041-01657 .
XO-1 lacks a trigonometric distance ; we estimate it to be 200 \pm 20 pc .
Of the ten stars currently known to host extrasolar transiting planets , the star XO-1 is the most similar to the Sun in its physical characteristics : its radius is 1.0 \pm 0.08 { R _ { \odot } } , its mass is 1.0 \pm 0.03 { M _ { \odot } } , V sin i < 3 km s ^ { -1 } , and its metallicity [ Fe/H ] is 0.015 \pm 0.04 .
The orbital period of the planet XO-1b is 3.941534 \pm 0.000027 days , one of the longer ones known .
The planetary mass is 0.90 \pm 0.07 { M _ { J } } , which is marginally larger than that of other transiting planets with periods between 3 and 4 days .
Both the planetary radius and the inclination are functions of the spectroscopically determined stellar radius .
If the stellar radius is 1.0 \pm 0.08 { R _ { \odot } } , then the planetary radius is 1.30 \pm 0.11 { R _ { J } } and the inclination of the orbit is 87.7 \pm 1.2° .
We have demonstrated a productive international collaboration between professional and amateur astronomers that was important to distinguishing this planet from many other similar candidates .