The colorful midnight sky

 Looking up at the sky near midnight, it seemed dark, but maybe slightly greyish rather than black.  The Sky Quality Meter gave a reading of sqml=21.52, which is nicely dark.  However, the camera revealed what the eye cannot see.  It is astonishing to find out what is going on overhead at the threshold of perception.

The Milky Way rising over McCall gulch on Snowshoe Mountain: 

Sony A7iii + Laowa 15mm f/2 + Sparkle-6 filter.  ISO 1600, 30 s.

 The Milky Way was overlaid with moving bands of green and purple airglow.  The four images  in this animation spanned an interval of about 7 minutes.  The two middle images used a Softon filter.

After capturing these images I was about to pack up and head indoors when I remembered some excellent photographic advice: "Always look behind you".  I turned around to see the constellation Leo sinking toward Bristol Head and got a complementary shot of the western sky:

Laowa 15mm f/2 + Sparkle-6 filter.

Some random images from another clear night

Last night was clear again, but with a measured sky brightness of sqml=21.44.  This is not quite as dark as previous nights.  The primary goal was to capture an image of asteroid (285) Regina. However, that quest was unsuccessful.  The asteroid was just too dim (mag 16) and too low in the sky (11°) where the airglow is strong.  Instead, here are some images obtained while waiting for the asteroid to emerge from behind the mountain ridgeline.  No sense wasting a clear dark night.

Corona Borealis.  Sony A7iii + Rokinon 85mm f/1.4 + softon filter.

The constellation Corona Borealis is worth monitoring because of an expected eruption of a recurrent nova sometime this summer.  When (if) it happens the new star will be comparable in brightness to Alphecca, which is the brightest star in this constellation.

 

Omega Centauri skimming the distant mountains.  Rokinon 85mm.

Near the top edge of the above image is a fuzzy blob that is the galaxy known as Centaurus A.  This is a strong radio galaxy that is also the 5th brightest visually.  It is thought to be the product of a long-ago collision between an elliptical galaxy and a smaller spiral galaxy.  It contains a supermassive black hole with a mass of about 55 million suns.

Antares (left), M4 (right), and NGC 6144 (top edge).

This image was obtained with an Astro-Tech 80mm ED f/6 triplet refractor with a 0.8x reducer and a 0.71x reducer for a final focal length of 273mm f/3.4.  The camera was an Olympus E-M5iii at ISO 1600, 60 s.  A ZWO AM3 mount was used for tracking.

The three objects of interest in this frame are at vastly different distances. Antares is a red giant star 550 ly distant.  The globular cluster M4 is 7200 ly away and is the closest of this type to earth.  The globular NGC 6144 near the top edge of the frame is more than four times farther away at 29,000 ly. 

Milky Way and airglow

 Milky Way season is coming.  Currently, now at the end of May, the Milky Way rises over the southern flank of Snowhoe Mountain around midnight.  A month later, near the end of June, it will be rising two hours earlier.

Last night the sky brightness was measured (near the zenith) as sqml=21.60 mpsas, a very respectably dark value.  What the unaided eye can not easily see is the strong airglow at low elevations.  The camera, however, records it easily and it makes a colorful overlay on the distant star clouds of the Milky Way.

These images were obtained with a Sony A7iii + Sony 20mm f/1.8 G lens (ISO 1600, 30s on a tracking mount).

The Milky Way rising over McCall Gulch on the southern flank of Snowshoe Mountain:

Sparkle-6 filter.

Softon-A filter.

Softon-A filter.

Sparkle-6 filter.

Airglow is caused by the night-time recombination of molecules dissociated by UV light from the sun.  It occurs at altitudes near 100 km and higher, which is considered to be the boundary of space.  Green and purple colors arise from different molecules that stratify at different altitudes.  It is possible to see moving bands of color in images taken only minutes apart.  Airglow imposes a natural limit to how dark the sky can get when viewed from the Earth's surface.

Airglow is not a static feature.  Here is what it looked like about 1/2 hour before the previous images:

 

As usual, click on an image to enter Gallery View and get access to the full-size versions.

Scorpius rising

 The Flower Moon of May has exited the evening sky.  It is dark again.  Last night the sky brightness was sqml= 21.66 mpsas.  The wind laid down around 10pm, so it was time to take advantage of the evening calm.

Scorpius rising over a southern ridge of Snowshoe Mountain.

The photo above was taken with an Olympus E-M1iii + Sigma 30mm f/1.4 lens and a Hoya Softon-A filter (ISO 1600, 60 s), riding on a Sky-Watcher Star Adventurer tracking mount.  The orange star just above the dark ridgeline is Antares, the 15th brightest star.

This view was obtained 45 min later using an Olympus 75mm f/1.8 lens and no filters.  In both of these images there is some green airglow evident in the lower part of the frame.

The quadrilateral figure formed by the bright stars of the constellation Corvus (the Crow) is hard to miss in the southern sky:

Corvus.  Sigma 30mm f/1.4 + Hoya Sparkle-6 filter.

In this image the bright star in the upper left corner is Spica (Alpha Virginis), the 16th brightest star.  When Spica crosses the southern meridian the giant globular cluster Omega Centauri will be skimming the horizon almost directly below.

Omega Centauri skimming the horizon.  Olympus 75mm f/1.8.

In this image Omega Centauri is reddened by its low position in the sky.  It is also veiled by bands of murky airglow.

High in the sky the constellations Hercules and Corona Borealis (Northern Crown)  stand above the airglow.

Hercules (lower left) and Corona Borealis (upper right). 30mm f/1.4 + softon.

Hercules  and Corona Borealis.  30mm f/1.4 + Sparkle-6.

The constellation Corona Borealis is worth watching.  It contains a recurrent nova that is expected to flare up sometime this year.  When it does this star will briefly be comparable in brightness to the brightest star in this constellation and the Northern Crown will gain a new (temporary) gem.

Star trails in the moonlight

 We had all the possible weather yesterday in Creede:  sun, wind, rain, sleet, and snow.  Just another day in the mountains.  And then things calmed down, the clouds disappeared, and the night was lit up by the Moon just two days before the May 23 full Flower Moon.

The stars in the northern sky traced out 15-deg arcs during a 1-hour exposure:

Olympus E-M1iii + Laowa 7.5mm f/2.  Live-composite mode.

This one-hour exposure also captured some meteors.  There is a bright meteor trail at the top middle of this cropped image.  Three nearly horizontal fainter streaks seem to point back to a common origin in the northeastern sky.

This was also an opportunity to test an old (but good) manual focus lens: a Vivitar Series 1 135mm f/2.3.  This lens dates back to the mid 1970's, so it is nearly 50 years old.  That was a time when the Vivitar Series 1 lenses were considered competitive with the offerings from the major camera manufacturers.  Here is Capella again, setting over the Bristol Head ridgeline:

Sony A7iii + Vivitar  Series-1 135mm f/2.3.  ISO 800, 10 s.

The short 10-s exposure prevents the mountain foreground from blurring too much as the camera tracks the stars.

In the northeast, Deneb and Sadr were rising over the La Garita mountains:

Sony A7iii + Vivitar Series-1 135mm f/2.3.  ISO 800, 10 s.

Deneb is the brightest star in the constellation Cygnus and the head of the Northern Cross.  It is the 15th brightest star in the sky.

The measured sky brightness increased from sqml=19.35 to 18.95 as the Moon rose higher in the sky.  The sky in Santa Fe is typically around 19.5 on a moonless night , so these readings are a testament to the clear and thin air in Creede.

Camera and lens on a tracking mount.

Starscapes by moonlight

 Last night the moon was 8.9 days old (time since new moon) and 66% illuminated.  The bright moonlight presents a challenge for normal astrophotography. However, it also provides an opportunity for some interesting starscapes because the surrounding landscape is lit up while the stars are visible.

Capella setting over Bristol Head:

Sony A7iii + Rokinon 85mm f/1.4 @ f/2.8 + softon filter.  ISO 800, 20 s.

Sony A7iii + Rokinon 85mm f/1.4 @ f/2.8 + sparkle-6 filter.  ISO 800, 20 s.

Capella is the sixth brightest star in the sky with a magnitude of 0.1.  The only brighter stars visible from Creede are Sirius, Arcturus, and Vega.

The sparkle filter is really too strong to use at this focal length.  It works better with focal lengths of about 30mm and shorter. However, because of the way it spreads out the light it does a remarkable job of preserving star colors.  The red star top center is Pi Aurigae, a red giant star.  The color is much more obvious with the sparkle filter than the softon filter. 

Turning south, it was possible to see the giant globular cluster Omega Centauri gliding along above Piedra Peak.  Omega Centauri has about 10 million stars and contains about the same mass as the supermassive black hole at the center of our galaxy.

 

Olympus E-M5iii + Canon FD 300mm f/4L + Metabones speedbooster.  ISO 1600, 20 s.  Effective focal length = 213 mm f/2.8.

Toward the southeast, Antares and the constellation Scorpius were rising above the southern flank of Snowshoe Mountain.  Antares is the orange star left of center.  The globular cluster M4 is right of center.  Antares is the 15th brightest star. M4 contains about 100,000 stars and is the closest globular cluster to earth (about 6000 ly).

Canon FD 300mm f/4L + Metabones speedbooster.  ISO 1600, 30 s.

Three globular clusters captured last night with the Canon FD 300mm:

M13 (left), M4 (center), Omega Centauri (right). 1-deg FOV.

The background in the M13 image is much darker because it was opposite from the moon, where the sky was darker.

Aurora over Creede

An unusually strong solar storm hit the Earth on Friday May 10 causing auroras that were seen as far south as Puerto Rico.  The storm is apparently persisting through this weekend.  It has been cloudy and snowy here in Creede, but there was a brief thinning of the clouds last night (Saturday).  

11 May.  Sony A7iii + Laowa 15mm f/2 + sparkle-6 filter.

  That is what the camera saw (ISO 1600, 30 s), but I could not detect the glow with my unaided eyes.  The north star Polaris is in the center of the frame, the Big Dipper at the top.

Three-frame animation.  30 s exposures.

 

The Little  Dipper through auroral glow.  Laowa 15mm f/2 + sparkle-6 filter.

credit: SkySafariAstronomy.com

Omega Centauri

 Omega Centauri is the name of a globular cluster in the southern constellation Centaurus.  This cluster is the largest globular cluster in our Milky Way Galaxy.  The number of stars (about 10 million), the mass (about 4 million solar masses), and the spectral distribution of stars support the hypothesis that this cluster is the remnant core of a dwarf galaxy captured by the Milky Way.

With a declination of -47.6° this cluster never rises more than 4.6° above the (sea-level) horizon at the latitude of Creede (37.8°).  This is a problem, because our local horizon is mostly obscured by the surrounding mountain peaks and ridges.  From my backyard observing location the view is blocked by the southern flank of Snowshoe Mountain and a neighbor's cabin.  From the front yard, however, there is a view south toward Piedra Peak where I can watch this cluster glide just a couple degrees above the distant peaks.

Omega Centauri emerging from the southern flank of Snowshoe Mt, 08 May, 11:23pm MDT.

 

 This image was obtained with a Canon FD 300mm f/4L lens and an Olympus E-M1iii camera (ISO 1600, 20 s) just as the cluster was transiting the meridian, its highest point in the sky.  The sky brightness (near the zenith) was sqml=21.48.

Here is a closer look with a 1° field-of-view (ISO 1600, 60s):

Omega Centauri.  E-M1iii + Canon FD 300mm f/4L. 2x binning.

Omega Centauri is an impressive sight in a small telescope or even binoculars. Here is a comparison to the "Great Hercules Cluster", M13:

M13 (left) and Omega Centauri (right).  Canon FD 300mm f/4L.

The Hercules cluster M13 has about 500,000 stars, or roughly 1/20 as many as Omega Centauri.  An interesting fact is that the total mass of all the stars in Omega Centauri is nearly the same as the mass of the supermassive black hole at the center of our galaxy. The Milky Way's central black hole has a radius less than half of the orbit of Mercury, while Omega Centauri spans about 150 ly.

Two years ago a waxing crescent moon lit up the sky as Omega Centauri emerged from behind Snowshoe Mountain.  In the image below the silhouette of Piedra Peak is in the lower right corner, the bright rectangle near the bottom is a neighbor's cabin window.

02 June 2022.  E-M5iii + Rokinon 135mm f/2.  ISO 1600, 60 s.

A comparison with the crescent moon that was setting over the flank of Bristol Head shows the relative size of this cluster:

Omega Centauri and the Moon.  E-M5iii + Rokinon 135mm.  02 June 2022.

When the faintest stars of the cluster are accounted for it has an angular diameter slightly larger than the moon.

Somewhat higher in the sky from Omega Centauri is the barred-spiral galaxy M83:

M83.  Canon FD 300mm f/4L.  1-deg FOV.  ISO 1600, 60 s.

 M83 is known as the "Southern Pinwheel Galaxy." Here is a finder chart:

 

credit: SkySafariAstronomy.com

Sirius setting over Bristol Head

 Sirius is the brightest star in the sky and rules the night in the northern-hemisphere winter.  As spring advances toward summer it hangs low in the SW.

This image was a 1-sec exposure (ISO 1600) using a Tokina AT-X 100-300mm f/4 zoom with a Metabones Speedbooster.  The effective focal length was 213 mm at f/2.8.

Sirius

Later in the evening I was evaluating a different lens, a Canon FD 300mm f/4L.  The following image is the great globular cluster M13 in the constellation Hercules.  Hercules rises in the NE in the late evening.  The sky brightness was sqml=21.68.

M13, 2° FOV.  E-M1iii + Canon FD 300mm f/4L.  ISO 1600, 60 s.

This lens is also superb for daytime use.  These early-morning elk were about 1 km away on the hillside across the Rio Grande:

 

Fresh snow on Bristol Head, 06 May

The Big and Little Dipper

 This time of year the two asterisms known as the Big Dipper and Little Dipper stand high in the northern sky.  These two star patterns are part of the formal constellations Ursa Major and Ursa Minor.

Sony A7iii + Laowa 15mm f/2 + Softon filter.  ISO 1600, 30 s.

Little Dipper.  Hoya Softon filter.

Sony A7iii + Laowa 15mm f/2 + Sparkle-6x filter.  ISO 1600, 30 s.

Little Dipper.  Hoya Sparkle-6x filter.

I like both of these two filters.  The Softon filter gives the stars a more natural appearance.  The Sparkle-6 filter results in a more artistic flair.

For those not familiar with these star patterns, here is a finder chart:

credit: SkySafariAstronomy.com

The sky brightness when these images were obtained was sqml=21.69 mpsas.  See the previous post for an explanation of this number.