NGC 3521 is a stunning galaxy located in the constellation of Leo, which is Latin for "lion." It is a type of galaxy known as a flocculent spiral galaxy, characterized by its loosely wound spiral arms that appear to be patchy or clumpy, giving it a unique and intriguing appearance.The Flocculent Spiral Galaxy is estimated to be about 40 million light-years away from Earth, making it relatively close by cosmic standards. It has a relatively large angular size of about 8.3x4.5 arcminutes, which means it is easily visible in amateur telescopes.One of the most prominent features of NGC 3521 is its distinctive spiral structure. Its spiral arms are composed of dust, gas, and billions of stars, and they extend outward from a bright central nucleus. The arms appear to be loosely wound and not tightly defined, with clumps of stars and patches of dark dust interspersed along the arms, giving it a "flocculent" or fluffy appearance. This is in contrast to grand design spiral galaxies, which have well-defined, tightly wound arms.The Flocculent Spiral Galaxy also exhibits a beautiful blue color, indicating the presence of young, hot stars that are actively forming. These young stars are concentrated in the spiral arms, where they are born from the gravitational collapse of gas and dust, and their intense ultraviolet radiation causes the surrounding gas to glow in a characteristic blue hue.In addition to its striking spiral structure, NGC 3521 also possesses a bright and compact central nucleus, which is thought to harbor a supermassive black hole at its core. This central region is surrounded by a bright stellar bulge, which is a concentration of stars that appears as a rounded, elongated structure at the center of the galaxy.

NGC 3521 also straddles the celestial equator, which is the imaginary line on the celestial sphere corresponding to Earth's equator.Overall, NGC 3521, the Flocculent Spiral Galaxy in Leo, is a captivating and visually stunning galaxy with its unique and intriguing appearance, making it a popular target for amateur and professional astronomers alike.



Older Version

This beautiful flocculent spiral galaxy in Leo straddles the celestial equator (see the Sky plot).  The core is in the southern hemisphere and perhaps 25 percent is in the northern hemisphere.  Given that its brightness and size are comparable to M96, it is regarded as surprising that Messier missed it (but he is likely to be distracted by a number of nearby groupings of such comparable galaxies).

The colors are directly as given by PhotometricColorCalibration and only the saturation increased. It is very easy to over-process this galaxy, which in the end distracts from its subtle features and appearance.

In processing, I've develop a few thousand lines of PixInsight JavaScript Runtime (PJSR) code to free myself from the tedious error-prone GUI driven PixInsight processing.  One main features of the processing is a scale-aware (arcsec/pixel) star removal.  In the end I don't apply any star reduction other than some very mild deconvolution to fix slightly elevated RA tracking errors (relative to Dec).