Northern Sky Narrowband Survey

This category contains results from the Northern Sky Narrowband Survey, which began at the end of 2018. The focus of this project is on the emission lines of HII (656.3 nm), OIII (500.7 nm), and SII (671.7 nm and 673.0 nm), but continuum data are also collected. The entire northern sky down to a declination of -16° is being surveyed.

A description of the equipment can be found on the instruments page. Almost any of the images produced by the survey show faint nebulae that haven't been cataloged before (which does not mean they are unknown). An attempt to list these objects can be found on the Uncataloged objects page.

Data releases

Below is an overview of the results published so far. Follow the links for data access and documentation.
DR0.1 (October 2024)
  • First complete set of Hα and continuum data
DR0.2 (May 2025)
  • First complete set with [OIII] and [SII] data.
  • Updated Hα and continuum data.

What we can see in the results

Interstellar matter consists in gas and molecules (dust). The latter scatters and reflects light from the stars. This matter, together with the stars, can be seen in continuum light.

The gas can be ionized, which means that the atoms or molecules lose electrons. This can occur as a result of high-energy electromagnetic radiation or due to collisions with other particles. (A similar mechanism is excitation, where the electron is just transferred to a higher, more energetic, orbital shell. In practice, excitation is much less probable than ionization because it only occurs at certain energy levels.) The energy required for this process is released as a photon as soon as the ions and electrons recombine and the electrons fall to lower energetic states. The transition between these states determines the energy of the emitted photon, and thus its wavelength. The resulting emission lines are observed by the survey using narrowband filters.

The observed ionic species are:

HII
(Singly) ionized hydrogen atoms are detected at a wavelength of 656.3 nm. This specific emission line is denoted as Hα. Since hydrogen is almost everywhere and can only be singly ionized, Hα light can be seen almost everywhere ionization occurs.
OIII
Doubly ionized oxygen atoms (which have lost 2 electrons) are detected at a wavelength of 500.7 nm. This is an emission line that only occurs it extremely low densities, which is why it is called a forbidden line, denoted by square brackets: [OIII]. The ionic species OIII can only be seen in highly ionized regions where oxygen is present.
SII
Singly ionized sulfur atoms (which have lost 1 electron) are detected at wavelengths of 671.7 nm and 673.0 nm. These (unspecific) forbidden emission lines are denoted as [SII]. The ionic species SII can be seen where sulfur is present and the ionization energy is relatively low (typically in the outer regions of nebulae), because in higher ionized regions, other species of sulfur dominate.

Images

Below are some results produced from the latest data release. Click on the preview images to see a larger version with a description.

Milky Way from Perseus to Monoceros: Orion-Eridanus Superbubble and dense molecular clouds Milky Way from Perseus to Monoceros:
Orion-Eridanus Superbubble and dense molecular clouds Nebulae above the galactic plane High galactic latitude nebulae around celestial north pole Milky Way from Cygnus to Perseus Milky Way from Cygnus to Perseus:
Many prominent emission nebulae Nebulae below the galactic plane Nebulae below the galactic plane Milky Way from Serpens Cauda to Cygnus: A region full of supernova remnants Milky Way from Aquila to Cygnus:
A region full of supernova remnants Dense region of the Milky Way near Aquila Hundertwasser-Corner:
Nebulae that appear to be created using a ruler Dense region of the Milky Way near Aquila Milky Way from Scutum to Aquila:
Star fields behind dark nebulae SH2-27 (Zeta Ophiuchi Nebula) behind molecular clouds SH2-27 (Cobold Nebula, ζ Ophiuchi Nebula) behind molecular clouds

Images from before the first data release

Below are older results created from early data. These images were processed differently than the newer ones. In particular, no continuum subtraction was applied. Click on the preview images to view larger versions with detailed descriptions.

OIII arc in Gemini OIII arc in Gemini Milky from Perseus to Cassiopeia Milky from Perseus to Cassiopeia Milky Way in Cassiopeia and Cepheus Milky Way in Cassiopeia and Cepheus HII region around California Nebula (NGC 1499) HII region around California Nebula (NGC 1499) Milky Way in Cygnus Milky Way in Cygnus Milky Way from Vulpecula to Aquila Milky Way from Vulpecula to Aquila Milky Way from Scutum to Ophiuchus Milky Way from Scutum to Ophiuchus Orion region Orion region Milky Way from Taurus to Perseus Milky Way from Taurus to Perseus M33 to SH2-126 M33 to SH2-126 Milky Way from Monoceros to Gemini Milky Way from Monoceros to Gemini

Monitor calibration

For optimal display, the monitor should be calibrated so that as many shades of the grayscale shown below are distinguishable. At least the 4% steps should be separated by every monitor. The 2% steps are visible on better monitors. To distinguish the 1% steps, a HDR monitor is required.

gray scale

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