A four-color stellar photometric system devised by B. Strömgren. It is based on measurements in the ultraviolet (3500 Å), violet (4100 Å), blue (4670 Å), and yellow (5470 Å) regions of the spectrum. T
he filters bandwidths are 340, 200, 160, and 240 Å respectively. Also known as Strömgren four-color photometry.
A theoretical sphere of ionized hydrogen created by energetic ultraviolet photons of a hot, massive star embedded in a uniform interstellar molecular cloud and lying at the center of the sphere.
A gravitational lensing phenomenon in which the image distortion is strong enough to be readily recognized, such as in the case of the Einstein cross or when giant luminous arcs show up in galaxy clus
ters (e.g. Abell 2218). Opposite to weak gravitational lensing.
A gravitational lensing phenomenon in which the image distortion is strong enough to be readily recognized, such as in the case of the Einstein cross or when giant luminous arcs show up in galaxy clus
ters (e.g. Abell 2218). Opposite to weak gravitational lensing.