Tag: Cosmos

The North America Nebula (NGC 7000 or Caldwell 20) is an emission nebula in the constellation Cygnus, close to Deneb (the tail of the swan and its brightest star). The apparent shape of the nebula resembles that of the continent of North America, complete with a prominent Gulf of Mexico.

There’s much more to this image than what you initially think you see. Layers upon layers of gases in space create illusions. There’s A massively bright star illuminating all of the gases you see. It’s all the same gas field. There’s a huge Dark Nebula so thick that the light from that massively bright star cannot penetrate it – creating the illusion of a gulf of Mexico and a divide between the “two” nebula. Another layer nature added for contrast I’m sure is the Cygnus wall lining the left edge of the nebula. Cygnus’s Wall is a term for the “Mexico and Central America part” of the North America Nebula and exhibits the most concentrated star formations in the nebula. It too is so dense light from behind it does not pass through.

The North America Nebula is part of the same interstellar cloud of ionized hydrogen (H II region) as the Pelican Nebula, separated by a dark band of dust, and listed the two nebulae together as Sh2-117. American astronomer Beverly T. Lynds catalogued the obscuring dust cloud as L935 in her 1962 compilation of dark nebulae. The distinctive dark nebula known as LDN 935 (it should perhaps be called the Hudson Bay nebula). This dark nebula lies at the front of the North America nebula and it blocks the light behind it.

Seeing it: The North America Nebula covers a region more than ten times the area of the full moon, but its surface brightness is low, so normally it cannot be seen with the unaided eye. Binoculars and telescopes with large fields of view (approximately 3°) will show it as a foggy patch of light under sufficiently dark skies. However, using a UHC filter, which filters out some unwanted wavelengths of light, it can be seen without magnification under dark skies. Its shape and reddish color (from the hydrogen Hα emission line) show up only in photographs of the area.

Size: The North America and Pelican nebulae lie 2,590 light years away (795±25 parsecs). The whole HII region Sh2-117 is then 140 light years across, and the North America Nebula stretches 90 light years north to south.

What lights it?: In 2004, European astronomers Fernando Comerón and Anna Pasquali searched for the ionizing star behind L935 at infrared wavelengths, using data from the 2MASS survey, and then made detailed observations of likely suspects with the 2.2 m telescope at the Calar Alto Observatory in Spain. One star, catalogued J205551.3+435225, fulfilled all the criteria. Lying right in the centre of Sh2-117, with a temperature of over 40,000° K, it is almost certainly the ionising star for the North America and Pelican Nebulae.

Later observations have revealed J205551.3+435225 is a spectral type O3.5 star, with another hot star (type O8) in orbit. J205551.3+435225 lies just off the “Florida coast” of the North America Nebula, so it has been more conveniently nicknamed the Bajamar Star (“Islas de Bajamar,” meaning “low-tide islands” in Spanish, was the original name of the Bahamas because many of them are only easily seen from a ship during low tide).

Although the light from the Bajamar Star is dimmed by 9.6 magnitudes (almost 10,000 times) by the dark cloud L935, it is faintly visible at optical wavelengths, at magnitude 13.2. If we saw this star undimmed, it would shine at magnitude 3.6, almost as bright as Albireo, the star marking the swan’s head.

I hope you find this photo as interesting as I do. So much to see.

Cheers!