Late-Night Wonders under a 21.84 sky

The measured sky brightness directly overhead last night was an astounding 21.84 mpsas.  This continues a several-day trend of some of the darkest skies I have seen in Creede for quite a while.  The sky becomes brighter toward the horizon because of airglow, a natural phenomenon in the upper atmosphere.  This low-elevation brightness is evident in the following image of Omega Centauri. 

 Omega Centauri is the largest globular cluster in our galaxy, containing approximately 10 million stars.  May is the best month for viewing this cluster from Creede.  Near midnight it skims along the southern horizon just above the peaks of distant mountains.

All of the images in this post were taken with an Olympus E-M1iii camera and Olympus 75mm f/1.8 lens.  Exposures were generally 60 sec at ISO 1600.

looking south

 In this image Omega Centauri is about to pass (about 10 minutes later) 1.8 deg over the top of Piedra Peak.  Directly above it near the top of the image is the fainter galaxy NGC 5128, otherwise known as Centaurus A.  Airglow gives the sky a faint green coloration.

Omega Centauri

 

Centaurus-A, NGC 5128

Just before midnight, Scorpius and its brightest star Antares are rising above the ridgeline of Snowshoe Mountain:

Antares, M4, and the Rho-Ophiuchi Nebula

 To the west, the bright "Beehive Cluster" (M44) and fainter nearby cluster M67 are sinking toward the Bristol Head ridgeline:

M67 (left) and M44 (right)

 

M67

M44

The dwarf galaxy Leo I lies only 12 arcminutes from Regulus, the brightest star in the Constellation Leo and the 21st brightest star.  This galaxy was discovered in 1950 with the 48-inch Schmidt camera at Palomar Observatory.  Today it is possible to image this galaxy with a 42-mm aperture camera lens in a 60-sec exposure.  Technology has come a long way in 76 years.

Regulus (center) and Leo I (up and to the right)

 The galaxy Leo I is believed to be the most distant satellite galaxy of our Milky Way, at a distance of 820 kly.  Regulus is 79 ly distant, so this background galaxy is more than 10,000 times farther away.