BAA Baade's Window background radiation backscattering Baikonur Baily Baily's beads Baker-Nunn camera Baker-Schmidt telescope Balmer decrement Balmer lines Bamberga band spectrum bandwidth bar barium star Barlow lens Barnard's Galaxy Barnard's Loop Barnard's Star barred spiral galaxy barrel distortion Barringer Crater Barwell meteorite barycentre barycentric coordinates barycentric dynamical time baryons basalt basaltic achondrite basin Bayer letters BD beam beamwidth Bear Claw Nebula Bear Driver Becklin-Neugebauer Object Beehive Beijing Observatory Belinda Bellatrix Belt of Orion Bennett, Comet BeppoSax Berenice's Hair Besselian year Be star Beta Canis Majoris star Beta Cephei star beta decay Beta Lyrae star beta particle Beta Pictoris Beta Regio Betelgeuse Bethe-Weizsäcker cycle Bettina Betulia Bianca Biela's Comet Bielids Big Bang Big Bear Big Bear Solar Observatory Big Crunch Big Dipper Big Dog billion BIMA Array binary star binoculars bipolar nebula bipolar outflow Bird Nebula Bird of Paradise BIS black body black body radiation black drop black dwarf Black-eye Galaxy black hole blazar Blaze Star Blazhko variable blink comparator Blinking Nebula BL Lac object blue clearing blue moon Blue Planetary blueshift Blue Snowball blue straggler Bode's law Bode's Nebula Bok globule bolide bolometer bolometric correction bolometric magnitude Bolshoi Teleskop Azimutalnyi Boltzmann's constant Boltzmann's equation Bond albedo Bonner Durchmusterung Boötes Boss General Catalogue bow shock Boyden Observatory Bp star Brackett series Brans-Dicke theory breccia bremsstrahlung brightness brightness temperature Bright Star Catalogue British Astronomical Association British Interplanetary Society brown dwarf Brown-Twiss stellar interferometer B star B-type asteroid Bubble Nebula Budrosa Bug Nebula Bull burst burster butterfly diagram BY Draconis star Byurakan