Interstellar dust in the context of "Asteroidal dust"

Apparent magnitude (m) is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light caused by interstellar dust or atmosphere along the line of sight to the observer.

Unless stated otherwise, the word magnitude in astronomy usually refers to a celestial object's apparent magnitude. The magnitude scale likely dates to before the ancient Roman astronomer Claudius Ptolemy, whose star catalog popularized the system by listing stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined to closely match this historical system by Norman Pogson in 1856.

The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B stars. The most luminous member is the ~2nd magnitude yellow supergiant Mirfak, also known as Alpha Persei. Bright members also include Delta, Sigma, Psi, 29, 30, 34, and 48 Persei. The Hipparcos satellite and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster of ~560 light-years (172 pc). The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. As seen from the Earth, the extinction of the cluster due to interstellar dust is around 0.30.

The cluster is centered to the northeast of Alpha Persei. It has a core radius of 11.4 ± 1.4 ly, a half-mass radius of 18 ly, and a tidal radius of 70.6 ± 8.5 ly, with 517 members being identified within the latter. The cluster shows solid evidence of having undergone mass segregation, with the mean stellar mass decreasing toward the edge. The age of this cluster is about 50–70 million years. Cluster member stars show a near-solar metallicity, meaning the abundance of elements with atomic numbers higher than 2 are similar to those in the Sun. The cluster shows evidence of tidal tails, which are most likely of galactic origin.

NGC 6334 is a massive emission nebula and star-forming region located in the constellation Scorpius. It is colloquially known as the Cat's Paw Nebula, and can be found 3° to the west-northwest of the bright star Lambda Scorpii. NGC 6334 was discovered by English astronomer John Herschel on June 7, 1837, who observed it from the Cape of Good Hope in South Africa. It spans an angular area larger than the full Moon. This structure is located in the Carina–Sagittarius Arm of the Milky Way, at a distance of approximately 5.5 thousand light-years from the Sun.

This nebula is a high mass filamentary cloud structure spanning ~320 ly. In the visible part of the spectrum, NGC 6334 emits mainly in red (from hydrogen atoms) and blue (from oxygen atoms). The interior is heavily obscured by interstellar dust, with clumps ranging up to 3,000 M_☉ in mass. Although there is pervasive star formation throughout, several embedded star-forming regions have been identified from infrared and radio emissions. Four of these sites have formed H II regions. X-ray sources within the nebula show the presence of ten distinct stellar clusters, most of which are associated with already identified infrared sources and H II regions.