Seven sisters

A birthplace of stars in the constellation taurus.


The seven sisters and surroundings shine in this 4°x3° vista. Seven of the brightest stars are visible to the eye as the small dipper. The faint nebulosity cannot be seen unaided, a hint of the brightest part can be seen on clear nights through a 10cm or larger telescope. Part of the IFN can be seen in this image, stretching out far beyond the pleiades themselves. The actual nebulosity in this place reaches about 3 degrees, or 6 full moons!

About the picture
Capturing was done over 3 nights, for a total of 10 hours.
The telescope was wrapped in thermal blanket to prevent radiative cooling messing up the focus. Capturing was pre-programmed for the nights, with the telescope shutting down automatically at twilight or when the object was too low.

Processing was very simple. The only calibration is flat-fields. No darks or bias frames, because they are rejected as outlier pixels by the image integration, and subtracted as part of the background subtraction. The integration images were selected based on SNR, eccentricity, and star counts. Finally, a color balance was performed and a simple histogram applied.

Lessons learned
This is my first attempt at making a deep exposure of a single object. Capturing was done over 3 nights. Many lessons were learned.

Just after starting the session in twilight, I open the observatory roof. I notice it takes some hours (!) for the focus to settle sufficiently. Only by 11pm was I confident enough to leave the focus alone. Since this is quite unusual for such a small telescope, I figured the telescope tube not quite settling must be due to the radiative cooling of the black aluminum parts, exposed to the clear winter sky.
For the next 2 nights, I wrapped the entire setup into the thermal blanket (the kind used for car windscreens). This worked magic, and the focus was more or less stable within 1 hour. With the thermal blanket, the telescope doesn't ice over, and even if the temperature drops a 3°C to 4°C since last focus, it would still be sharp.

The last night, almost 2 hours of exposure were lost due to high clouds rolling in prematurely. The nebula was still visible, but the stars were halos. I decided to scrap this. Another 2 hours were lost due to guiding stopped suddenly, and for not correctly orienting the camera on the subsequent night.

The remainder was lost due to poor S/N, especially while the pleiades were too low above the horizon directly above a city. Guiding was mostly OK.
It shows that good results can be had when imaging near large cities.

Image information

Open clusters, Reflection Nebulae