section_path: Physical diameters/Near-infrared method
section_name: Near-infrared method
paragraph_text: Near-infrared method
  
  This method has been used by 2MASS as an adaptation from the previously used methods of isophotal measurement. Since 2MASS operates in the near infrared, which has the advantage of being able to recognize dimmer, cooler, and older stars, it has a different form of approach compared to other methods that normally use B-filter. The detail of the method used by 2MASS has been described thoroughly in a document by Jarrett et al., with the survey measuring several parameters.
  
  The standard aperture ellipse (area of detection) is defined by the infrared isophote at the K band (roughly 2.2 μm wavelength) of 20 mag/arcsec. Gathering the overall luminous flux of the galaxy has been employed by at least four methods: the first being a circular aperture extending 7 arcseconds from the center, an isophote at 20 mag/arcsec, a "total" aperture defined by the radial light distribution that covers the supposed extent of the galaxy, and the Kron aperture (defined as 2.5 times the first-moment radius, an integration of the flux of the "total" aperture).