NGC 2903 - Galaxy
In spring, when dusk approaches and the sky becomes darker, the prominent constellation of Leo rises in the east and with it a multitude of beautiful
galaxies just waiting to be observed. One of them is a bright galaxy with the designation "NGC 2903", that can be found next to the head of Leo -
more precisely about 1.5° south of the 4.3mag bright star "Lambda Leo", an orange supergiant of spectral type K.
The galaxy is quite bright with an apparent magnitude of 8.8 mag and with 12.6'x6' arcminutes also quite large. And so one has to wonder why Messier
did not include the galaxy in his catalog. Maybe he overlooked it? But finally the galaxy was found in 1784 by F.W. Herschel.
NGC 2903 is about 28 million light-years away from Earth and belongs to the Virgo Supercluster. With a diameter of 100,000 light-years it is only
a little smaller than our own Milky Way. The absolute magnitude is M= -20.6mag, which corresponds to a luminosity of 15 billion suns. With
Hubble- Type "SBbc" the galaxy belongs to the group of barred spirals. The bar contains 20% of the total galaxy mass, while the remaining mass is
distributed 75% to the disk and 5% to the bulge. Near the center, a region 2,000 light-years across can be seen, where 0.7 solar masses of stars are
formed each year - so it would take a year and a half to form a star like our Sun.
The supermassive black hole at the center of NGC 2903 has a mass of 9.1+-1.7 million suns, according to a 2008 paper.
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When pointing a 20" telescope at this galaxy, the first thing you notice is a rather bright core surrounded by a fairly large halo. The second look
goes immediately to the bar that runs through the halo.
The inner spiral arms show up next and wind at the end of the bar in opposite directions. They give the galaxy the well known S-shape. With the
outer spiral arms it is such a thing. They are quite faint and show up only at higher magnification. Even with 50cm aperture it is not easy to follow
them.
All in all a beautiful galaxy, which by the way also tolerates very high magnifications up to half of the mirror diameter.
