Ebre Observatory is located at Roquetes (Baix Ebre) on the top of a small hill 50 m. a.s.l. The geographic coordinates are: Latitude 40° 49' 14'' N., Longitude 0° 29' 36'' E.

The Observation Unit of Ebre Observatory dedicates part of its activity to the solar photospheric observation, taking every day an image of the Sun, if the meteorological conditions allowed. This new bulletin is a summary of the observations and measurements done between 1 January and 31 December 2013, with a total amount of 251 images, which is a 68% of the days. The Wolf’s number data began in 1943 and from that time the hemispheric separation (North and South), as well as its difference (N – S) were calculated.

The data are presented in this bulletin mainly in graphic from, with a monthly table, and for every day it is possible to see the solar image. Those days which are not present on the table are days without observation.

In order to carry out the daily observation of the solar photosphere we have a telescope Zeiss APQ 150/1200 with a resolution of 0.7 arc seconds and with a digital camera DALSA CA_D4 with 1024 x 1024 pixels and a pixel size of 12 x 12 μm. The image is capturated with the SAISS II software provided by the Instituto de Astrofísica de Canarias. Then the image is treated using software developed at the observatory. Thus for each picture the number of groups (G), the number of spots (q) and Wolf number (W=10*G + q) are determined. For each spot, among others parameters, we measure its size in number of pixels, its area in millionths of hemisphere, and the grey level. In relation to the groups we determine the heliographic latitude and longitude, its area, the number of spots which compose the group as well as the group class. Also, a parameter related to the quality of the image, is given. It varies from 1 to 5.

The daily image of the Sun can be seen at our web page www.obsebre.es