I shot H-alpha filtered lights for this image at many nights, after I shot lights for my Cygnus mosaic project.

After a midnight, Cygnus and its targets are too low in the horizon so I used rest of the night for this supernova remnant. Total exposure time for H-alpha, ~13h.

Simeis 147 (sharpless 240), is a very faint and very large supernova remnant in constellation Taurus at distance of ~3000 light years. It's constantly expanding at speed of 1000 km/second but due the size of it, we can't see any movement in it. This SN spans over 160 light years and the apparent scale in the sky is about three degrees (Moon has an apparent size of 30" = 0,5 degrees). Explosion took place approximately 30.000 years ago and left behind a pulsar (Neutron star). The pulsar has recently identified.

EDIT

I just did a small calculation, how long it takes to this supernova remnant to expand 1% large when the diameter is 160 light years and it expands at speed of 1000km/second.

Answer is ~480 years.

(1% of diameter 160/100= 16, as kilometers ~151.372.800.000.00, = Y, km,

1000km/second is ~315.360.000.00, = Z, kilometers/year.

So, X x Z = Y and X=Z/Y, X = 480 with given values)

This is a difficult target to image and image above is my second try to capture it. An older version can be seen here. This older image was my second APOD from NASA.

Technical details:

Processing work flow:

Image acquisition, MaxiDL v5.07.

Stacked and calibrated in CCDStack2.

Deconvolution with a CCDStack2 Positive Constraint, 33 iterations, added at 33 % weight

Levels, curves and color combine in PS CS3.

Optics, Canon EF 200mm camera lens at f1.8

Camera, QHY9

Guiding, Meade LX200 GPS 12" and a Lodestar guider

Image Scale, ~5,5 arcseconds/pixel

H-alpha 34x900s, Binned 1x1 = 8,5h

H-alpha 24x1800s, Binned 1x1 = 12h

O-III 60 x 300s, Binned 3x3 = 5h

S-II 6 x 600, Binned 3x3 = 1h

Total exposure time for Hydrogen alpha alone is ~20,5h

Total exposure time is 26,5h