Star clusters at two focal lengths

 The sky brightness has been poor the last couple nights, with a measured value of sqml=19.38 mpsas.  There appears to be a very thin cloud or haze layer, but it is clear enough to experiment with some star-cluster photography.

Equipment used: Rokinon 135mm f/2 lens with an Olympus E-M5, and a SkyWatcher SkyMax 102 MCT with a Sony A7iii.  Exposures were limited to between 20 and 30 sec because of the sky brightness.

M36 (LL) and M38 (UR) in Auriga.  Rokinon 135mm + E-M5, 20 sec.

 The Olympus E-M5 is the original version, bought new in 2012, so this is a 14-year-old camera.  At the time, this was a game-changer in the micro-four-thirds format.  It is still a good camera, but no longer my first choice for astrophotography.

M35 in Gemini.  Rokinon 135mm. 20 sec.

 The SkyMax 102 has a nominal focal length of 1300 mm, not quite ten times longer than the Rokinon.  The fully illuminated image circle from this scope is about 22 mm, slightly smaller than the 24mm height of the Sony "full-frame" sensor.  This corresponds to about a 1-deg FOV.

M35. SkyMax 102. 30 sec.

 There is a smaller and dimmer cluster to the lower right of M35.  This is NGC 2158.  It appears much smaller because it is almost six times farther away.

NGC 2158 at 135mm.  4x enlargement.

 

NGC 2158 at 1300 mm.

The limiting magnitude in both images is in the range of 14.5–15.  The 1300-mm image obviously has higher resolution.

 

M37 in Auriga.  SkyMax 102.

Hyperion: a dim and distant moon of Saturn

 Saturn currently has 274 known moons, ranging in size from planet-like Titan to others that are essentially large rocks less than a mile wide.  Last night (16 Jan) a SkyWatcher SkyMax 102 Maksutov-Cassegrain telescope was used to track down Hyperion, the eighth largest moon of Saturn.  Hyperion has an irregular shape, with its longest dimension being about 224 mi (360 km).  It is a dim moon with a visual magnitude of 14+.

The sky looked clear at 7:30 pm, but as darkness increased a thin cloud layer was visible.  This increased the difficulty of an otherwise successful capture of Hyperion.

The SkyMax 102 has a nominal focal length of 1300 mm and an aperture of 102 mm (4 in.).  It was used with an Olympus E-M5iii camera.

Five of Saturn's largest moons.  20 sec, ISO 1600.

 

Hyperion to the left of overexposed Saturn.  30 sec, ISO 1600.

Predicted moon positions.  Credit: SkySafariAstronomy.com

The SkyMax 102 was also used with a front-mounted solar filter to image some large sunspots currently traversing the sun:

16 Jan

 

17 Jan

With this telescope the sun's projected image barely fits on the micro-four-thirds sensor.

Moons of Saturn

 The Astro-Tech AT72EDII refractor, with it's 430 mm focal length and meager 72mm (2.8") aperture, is not an ideal planetary telescope.  In the not-so-dark skies of urban Santa Fe it is better suited to photographing or observing star clusters or the Moon and Sun.  However, it is fun to see what can be done with it.  So far it has picked up two moons of Uranus (Titania and Oberon) and a dim and distant moon of Jupiter (Himalia), none of which I had seen before.

Last night the scope was turned to Saturn, Neptune, and the dwarf-planet Ceres.

The current locations of Ceres, Neptune, and Saturn.  (credit: SkySafariAstronomy.com)

 Five moons of Saturn were visible in a 20-sec exposure:

 Four of the moons, Titan, Rhea, Dione, and Tethys are in a line with Saturn's ring plane.  The rings are hidden in the glare of the overexposed planet and are currently nearly edge-on.  A fifth moon, Iapetus, sits just above Saturn accompanied by a background field star.

Credit: SkySafariAstronomy.com

 Neptune is a more difficult target.  Last night, its largest moon Triton was separated by only 11 arcseconds from the planet.  It appears to be just-barely visible in a 5-sec exposure:

Neptune and Triton. 3x enlargement.

 

Credit: SkySafariAstronomy.com

 At magnitude 13.8, Triton requires a fairly large telescope to be observed visually.  It is about 77% the diameter of our Moon, and is larger than the dwarf-planet Pluto.

Ceres is the closest dwarf planet to Earth, orbiting in the main asteroid belt between Mars and Jupiter.  It is currently at magnitude 9, about the same as Saturn's moon Titan.

Ceres (circled).  1-deg FOV (vertical).

 The sky brightness last night was sqml=19.68, which is an improvement from the previous few days.  

Some more star-cluster pictures:

M34 in Perseus. 1-deg FOV.  30-sec exposure.

 

NGC 1582 in Perseus.  20-sec exposure.

M37 in Auriga.  25-sec exposure.

Himalia: a small and distant moon of Jupiter

 The four Galilean Moons of Jupiter are the most familiar planetary moons in the solar system.  They are bright enough to be visible to the unaided eye, if not for being lost in the glare of Jupiter.  They are an easy target for binoculars.  Ganymede, the largest moon, is larger than the planet Mercury and about 78% the diameter of Mars.

From left to right: Ganymede, Io, Europa, Callisto (11 Jan).

 Jupiter currently has 95 moons that are officially recognized, but all of them are much smaller than the big four.  The next two largest are Amalthea and Himalia, with diameters on the order of 100–200 km.  These two moons are also very faint, with visual magnitudes dimmer than magnitude 14.

Amalthea orbits too close to Jupiter to be picked up with small telescopes.  Himalia, on the other hand, is in a very wide orbit and therefore potentially accessible.  The problem with finding Himalia is that its orbit drifts rapidly enough over time that software programs with fixed orbital elements will not provide accurate positions.  This problem was circumvented by using the Horizons Web Application of the Jet Propulsion Laboratory to generate an ephemeris for Himalia and Ganymede.  The location of Ganymede was used to calculate an offset between the JPL coordinates and the coordinate system used by SkySafari.  The position for Himalia predicted by SkySafari was determined to be off by about 6.8 arc minutes. (SkySafari is an app for iOS and MacOS that is used to point the telescope and generate star charts.)

The following images were obtained using the Astro-Tech AT72EDII refractor at about 10:30pm on 11 January.

 

Overexposed Jupiter. The location of Himalia is circled. 2.4-deg wide FOV.

Himalia (circled).  0.5-deg FOV.  30-sec exposure, ISO 1600.

Comparison of the image of Himalia to other stars in the field indicates that it is shining at about magnitude 14.5.

The sky brightness was measured as 19.53 mpsas.  This is a very mediocre value for a moonless night in Santa Fe. Some other images obtained from the same session:

NGC 2264, the Christmas Tree Cluster in Monoceros.

 

Open cluster M41 in Canis Major (just below Sirius)

 

Open cluster M93 in Puppis.

Open clusters M46 (left) and M47 (right) and NGC 2423 (top) in Puppis.

Star clusters, an asteroid, Uranian moons

 Last night the sky was clear but not especially dark.  The measured sky brightness was sqml=19.35 mpsas, which is poor even for Santa Fe.  Only two stars in the Little Dipper were easily visible, an indicator of poor transparency.  These are not good conditions for photographing faint nebulae and galaxies.  Star clusters and solar-system bodies are better targets.

Equpment: Astro-Tech AT72EDII and Olympus E-M5iii camera, ZWO AM3 mount.

NGC 457, the "Owl Cluster" (LL) and NGC 436 (UR).

 

NGC 7789, "Caroline's Rose".

 Caroline's Rose and the Owl Cluster are open clusters in the constellation Cassiopeia.

Caroline's Rose (LL), Owl Cluster (top middle). credit: SkySafariAstronomy.com

 There is a trio of small open clusters near the star Kappa Cassiopeiae: NGC 146, NGC 133, and King 14.

Kappa Cassiopeiae and three small open clusters

 

credit: SkySafariAstronomy.com

M37, the "Salt and Pepper Cluster" in Auriga

The main-belt asteroid (10) Hygeia is currently in the constellation Taurus, shining at magnitude 10.8.  It is the fourth largest asteroid.

 Two moons of Uranus, Oberon and Titania, were discovered by William Herschel on 11 January 1787.  Oberon orbits with a period of about 14.0 days and Titania has an orbital period of 8.7 days.  Both moons shine at around magnitude 14.

Uranus, Oberon, and Titania.  2x enlargement

 

Two moons of Uranus and a dozen star clusters

 The Wolf Moon is waning and rising later.  These images were taken less than an hour before moonrise.  Sky brightness was a mediocre sqml=19.4 mpsas.  A thin cloud layer was visible toward the northwest.

Equipment: Astro-Tech AT72EDII refractor + 1x field flattener, Olympus E-M5iii camera, ZWO AM3 mount. 

First up, another look at two moons of Uranus: Titania and Oberon.  Both of these moons are about magnitude 14.  (Reminder: click on an image to get access to the full-size version.)

Uranus, Titania, Oberon., 2x enlargement.

4x

 

The Double Cluster in Perseus.  2-deg wide FOV.

Meissa (Lambda Orionis) and Collinder 69 (CR69) at the head of Orion.

Another double cluster.  NGC 1817 (left) and NGC 1807 (right) in Taurus.

NGC 1647 in Taurus

NGC 1746 in Taurus

M34 in Perseus

M36 in Auriga

M37 in Auriga

M38 and NGC 1907 (bottom) in Auriga

M45 in Taurus

That was actually thirteen star clusters, so a "Baker's Dozen".

Perihelion

 Today was doubly eventful.  This morning the first full moon of 2026 occurred at 3:04 am MST.  Seven hours later at 10:15 am MST the Earth reached perihelion (closest distance) in its orbit around the Sun.  The two events are totally unrelated.   The angular size of the sun is currently 32.5 arcmin or 0.542 deg.  I photographed it in both white light and Hydrogen-Alpha light.

Equipment:  Astro-Tech AT72EDII f/6 refractor + Kendrick solar filter for a "white-light" photosphere image, and a Lunt LS50THa double-stacked solar scope + ASI178mm camera for a view of the Hydrogen-Alpha chromosphere.

 

"white light"

Hydrogen-Alpha

Hydrogen-Alpha: negative, false-color

The negative, false-color image makes it easier to see the prominences.