Locomotoring

The first constellation that every child learns to recognize is the big dipper or Ursa Major (Saptrishi Mandal). Month of May, Ursa Major is overhead. Did you know that you can’t see Ursa Major from either of the poles? It is one of those things that I was theoretically supposed to know, but I didn’t know until someone said it out aloud. Life lesson – even the most commonplace can become the most elusive.

When I was in Antarctica, I did look up at the sky. I was there in the Antarctic summer, when the days are so long that one didn’t have nightfall. But here in Bay Area, when I look up, the Ursa Major is one of the few constellations I can still see with my naked eye. Hidden amongst its stars, is the littlest of gems – the Owl nebula, the small blue ball of fuzz. The Surfboard Galaxy, the little elliptical red fuzz comes with the Owl. This galaxy and its partner nebula are really really far away for our widefield 300mm lens. Even M81 (Bode’s Galaxy) and M82 (Cigar Galaxy), the brightest of the deep sky objects near Ursa Major (link) are far away, these are even further away.

The following bit is for myself – not just to nerd out but to track provenance. This was my first integration of light from two different color filters! The image processing uses Continuum Subtraction to extract the Green from the OIII filter and the Red from the Ha filter. Subsequently, the Ha is combined with the UVIR red channel. The OIII is combined with the UVIR green and blue channels using the following PixelMath formula.

Red Channel (UVIR_R)
Expression: Min( $T + (Ha * 1.2), 1.0 )
Green Channel (UVIR_G)
Expression: Min( $T + (Oiii * 2.0), 1.0 )
Blue Channel (UVIR_B)
Expression: Min( $T + (Oiii * 2.5), 1.0 )