With this work I begin exploring one of the most fascinating branches of astronomy accessible to an amateur today: differential photometry. This technique measures small variations in an object's brightness, down to thousandths of a magnitude, by comparing it with reference stars of constant brightness.
In this case we used the technique to detect an exoplanet, a planet beyond our Solar System, as it crosses the disk of the star it orbits, 700 light-years away. It seems incredible, but the result shows that it is relatively easy to achieve.
The exoplanet is designated HAT-P-19 b. It is a low-density gas giant without a solid core, completing an orbit around its star in just 4 days. It has a mass similar to Saturn's and an orbital radius of 0.046 AU. The star has an apparent magnitude of 12.9 and a mass of 0.84 solar masses.
The change in the star's brightness caused by the exoplanet transit is 22 thousandths of a magnitude, and the transit lasts about 170 minutes. In the transit graph we can clearly see the curve showing the change in luminosity and follow the motion of that extrasolar planet by analyzing the light from its star reaching our telescope. Fascinating, without a doubt.
