Introduction

Astronomical observatory in Ondřejov, a little town located 35 km south east from Prague (Czech Republic), was founded in 1898 as a private observatory. In 1928 the observatory was donated to state and Charles University, and from 1954 it became a part of Astronomical Institute of the Czech Academy of Sciences (ASU CAS). The first observation of the Sun in Ondřejov started in 1944 and nowadays the observatory, and its Solar Physics Department, has a long tradition of different kinds of solar observation and studies. In 1984 Solar Patrol Service (SPS) was established within the department and since that time, unfortunately with some breaks, it has been monitoring the Sun and compiling solar activity reports and flare forecasts (www.asu.cas.cz/~sunwatch/).

White light synoptic images are provided by SPS each sunny day (7/7, holidays included). The images are acquired approximately every 60 minutes by 150/750 mm telescope equipped with 12 bit CMOS camera (4656×3520 px; 1.05”/px) and full-aperture neutral density filter (AstroSolar Photo Film OD=3.8). Final images are stored as FITS files with 2200×2200 pixel size and also as preview images in jpg format.

Technical information

The observations are carried out at the Solar Patrol Service dome using the equipment:

• a 150-mm refractor with focal length 750 mm

• German equatorial mount Zeiss VII

• Camera: ZWO ASI1600MM, 12 bit, chip: CMOS, resolution in pix: 4656×3520, pixel size: 3.8×3.8 µm, resolution: 1.05 "/pix

• filter: Baader Planetarium AstroSolar OD3.8

• cadence: image per 1 hour

Raw images are recorded with full size of 4656×3520 pixels and a with dynamic range of 12 bit. As the original images are quite large, the archived FITS files are saved at reduced size of 2200×2200 pixels, having the solar disc approximately in the centre. Images are oriented within the daily motion of the Sun. More information can be found in FITS headers. No flat-field correction has been applied. No limb darkening correction has been applied.

The JPG images are produced mostly as the preview of FITS images. The image of the solar disc is rotated about the centre of the disc to have solar North up and West on the right.

Limitations and caveats of the product

The observation of the Sun can be carried out from 04:00 – 17:00 UTC in summer and from 08:00 – 13:00 UTC in winter at SPS site. During this time interval the Sun is monitored. The service is provided 7/7, holidays included. When the weather is cloudy the observations are not provided.

Use and functionality of the product

The Latest tab displays the latest image available. These are updated every hour. The data are also available in FITS format via the API.

The Archive tab provides an access to archived white light images since January 2022. By default it lists the last 10 days of observations. The list can be filtered out by providing start and end dates entry in the format YYYY-MM-DD. For example, entering the start date 2023-01-01 and end date 2023-01-30 and clicking the submit button will return all of the data available from January 2023. The data are also available via the API.

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