[2][4][5] The distance to W40 is 436 ± 9 pc (1420 ± 30 light years),[1] making it one of the closest sites of formation of high-mass O-type and B-type stars.

[4] Dust from the molecular cloud in which W40 formed obscures the nebula, rendering W40 difficult to observe at visible wavelengths of light.

[1] The W40 star-forming region is projected on the sky in the direction of the Serpens-Aquila Rift, a mass of dark clouds above the Galactic plane in the constellations Aquila, Serpens, and eastern Ophiuchus.

[13] The high extinction from interstellar clouds means that the nebula looks unimpressive in visible light, despite being one of the nearest sites of massive star formation.

A weak, bipolar outflow of gas flows out of the core, likely driven by a young stellar object, with two lobes differing in velocity by 0.5 km/s.

The Herschel results for W40 and the Aquila Rift, compared to those for molecular clouds in the Polaris region, suggest that star-formation occurs when the linear density (mass per unit length) exceeds a threshold making them susceptible to gravitational instability.

These observational results complement computer simulations of star-formation, which also emphasize the role that molecular-cloud filaments play in the birth of stars.