HAT-P-4b is sixteenth exoplanet that has beed successfully observed at THO. The measurements of the HAT-P-4b were made 10./11.5.2008 by the Veli-Pekka Hentunen and Markku Nissinen. The mother star, GSC 2569-1599, of the planet is F-class star that is larger than our Sun and the distance from the Earth is about 1010 light years. Planet is so called hot-Jupiter, that has a radius of 1,27 Rjup and revolution time only 3,06 days.

Despite the sky was a bit bright, the transit of the HAT-P-4b was observed with quite good accuracy. The mother star dimness during the transit was about 10 mmag according the THO measurements. The pictures were taken with 60 sec. exposure times and the photometric filter R was used. The comparison stars that were used were GSC 2569-1277 (C1), GSC 2569-744 (C2) and GSC 2569-778 (C3).

Observers: Veli-Pekka Hentunen ja Markku Nissinen