Friday Feb 4th… A rare coincidence between small moon and clear night. The initial real-life test of APT beta 3.95 passed fine and it was released. 

When the Moon was below the horizon decided that have to use the opportunity and to start my first planned multi-year project – to image NGC 1555 in several years to see how the brightness will change. To be honest I didn’t make deep research – variable nebula, in a favorite constellation, handy size and the plan was to spend just few hours. 

The result - 2 hours gathered before it got too low. These 2 hours are just on the limit for this object, but it is a start. There is data from this season If there is chance to add few more before it is gone will be great! 

Around this data I started to read more about the object and it happens to be very curious! In fact its main star is not exactly variable, it is not one and all of them are not exactly stars! 

So the T Tauri which lights the nebula NGC 1555 (also known as Hind's Nebula and Sharpless 238 ) gave it name to a whole class of stars – “T Tauri Stars” which are young (as it is modern to say “not young but young young” ), less than 10 million years, under 3 solar masses, the nuclear fusion is about to start and they can have random, periodic or combination of both variable brightness... 

The one in the Hind's Nebula is in fact three of these young bodies. Two very close around 7 AU separation (something like Sun and the space between Saturn and Jupiter, even they are orbiting with nearly the speed of Saturn) with masses ~2 and ~0.5 solar masses. The other “star” in the triad is around 300 AU away and is evaluated to ~2 solar masses. The orbiting period is almost unclear - between 400 and 14 000 years…  The distance from Earth is around 400 ly.

The variability is considered to be mainly random and is also considered to be caused by matter obstruction. The main part of the remaining proto ring of the whole system has formed a not uniform “circumbinary” ring surrounding the system. To make the things more fun – every body has its own proto planetary ring, each one with a different orbit inclination. The “circumbinary” ring is almost perpendicular to our point of view, but everything combined is causing brightness fluctuations in the surrounding nebula ( “The Three-body problem” ?!?! ;) )

The history of the nebula is also quite “fuzzy” and is defined  by the nature of the T Tauri system. It had been found and lost, rediscovered on close place and lost… It had been on the very limit of the scopes available in the 19th century and its variable nature caused lots of troubles and confusion

 So here is the result, not great… But the intention is to build foundation for comparison, not to have deep and beautiful image

https://www.astrophotography.app/