· · · ·
Proper NameNone
Bayer Designationf1 Orionis
Flamsteed Number69 Orionis
HR (BSC)2198
Right Ascension6h 12m 3s
Declination+16° 7' 49"
Distance529 light years
162 parsecs
MagnitudeApparent: +4.96
Absolute: -1.09
Spectral ClassB5Vn blue main sequence star
Optimum VisibilityJanuary
NotesThe most notable feature of f1 Orionis is its rapid rotation rate, estimated at 276 km/s, compared to just under 2 km/s for the Sun. This implies that the star is oblate or 'flattened' in form, with a bulge around its equatorial regions due to its rapid rotational rate.

One of a collection of stars that mark out Orion's upraised arm and weapon - either a club or a sword, depending on the particular depiction - that run northwards from the familiar group of bright stars representing the Hunter's body. f1 Orionis is one of a pair of blue dwarf stars designated 'f Orionis'. The other, f2 Orionis, lies somewhat to the east of f1. As well as falling close together in the sky, these two stars are also close together in space, each lying a little over five hundred light years from the Solar System. On the other side of f1 Orionis from f2 in the sky, nearby to the west, is a patch of light known of Lower's Nebula, though in reality this emission nebula is more than two thousand light years beyond either of the two 'f' stars.

f1 Orionis is the central blue star in this image, with f2 Orionis visible to the extreme east (left). The clouds of the distant Lower's Nebula are visible to the southwest. Imagery provided by Aladin sky atlas

Though designated a 'dwarf' or main sequence star, f1 Orionis is rather larger and brighter than the Sun, which is also designated a dwarf star. It has more than four times the Sun's diameter, and emits more than two hundred times as much light energy. The pattern of f1 Orionis' spectrum shows not only that it belongs to the B-type blue class of hot stars, but also that it is spinning on its axis at an unusually rapid rate.


Related Entries