Two easy double stars

 There are two double stars visible in the northeast in the late evening that are easily accessible to small telescopes.  They are Cor Caroli (Alpha Canum Venaticorum) and Mizar (Zeta Ursae Majoris).  Both are easy to find.  Mizar is the brightest component of a naked-eye double star in the handle of the Big Dipper, and Cor Caroli is easily identified by its proximity to the Big Dipper, as seen in the image below. 

Olympus E-M1iii + Olympus 25mm f/1.8.  ISO 800, 30 s. Sparkle-6 filter. sqml=19.8

Cor Caroli consists of two visual components of magnitudes 2.9 and 5.5 separated by 19 arcsec. Mizar is the brightest of the Mizar-Alcor pair that can be seen without a telescope.  With a telescope, Mizar presents as two stars of magnitudes 2.2 and 3.9, separated by 15 arcsec.

In each case, the two visual components are also spectroscopic binaries, meaning that both pairs are actually four-star systems.

Cor Caroli A+B.  Celestron C6 + Olympus E-M5iii. ISO 400, 1 sec.

 The two components of Cor Caroli are also designated α¹ and α², with α¹ being the fainter of the pair.  

 

Mizar A+B.  Celestron C6, ISO 400, 1/3 sec.

 I was able to split both of these doubles using a 50mm f/4 refractor at 20x with some careful concentration.  Both of them were easily split at 40x with no effort.

The telescope in the picture below is a TS-Optics 50mm f/4 ED refractor with a GSO Amici-prism diagonal and a Celestron XCel-LX 5mm eyepiece (approx 40x).  This setup perfectly matches the description of "small telescope".

 

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Star Landscape mode with the Canon G9X Mark II

 The Canon G9X-II pocket camera has three astrophotography modes: "Star Portrait", "Star Landscape", and "Star Trails".  In the previous post an example of the "Star Trails" mode was shown.  This post will show results from the "Star Landscape" mode.  This mode has more user-adjustable parameters.  The ISO was set to 800 and the exposure was 15 sec at f/2.  The camera was mounted on a Vixen Polarie star tracker.

Star Landscape: Orion, the Winter Triangle, and Jupiter.

The "Winter Triangle" asterism comprises Sirius (lower left), Procyon (upper left), and Betelgeuse (center).  Jupiter is the bright star at right center edge.  

The G9X offers three options for star processing: Sharp, Off, and Soft.  The above image was obtained using the "Soft" setting.  This mimics the effect of a diffusion filter and is supposed to give a better representation of relative star brightness.

The next three images show the effect of the three settings:

"Sharp" setting

"Off"

"Soft"

There is some astigmatism visible around the edges at f/2, but no worse than many lenses used on interchangable-lens cameras.

Sirius ("Sharp" setting)

 

Sirius ("Soft" setting)

Star trails with a pocket camera

 The Canon G9X Mark II pocket camera was released in 2017.  My copy was purchased in 2020.  It has several astronomy-related scene modes which I have never utilized, until now.  The three modes are "Star Portrait", "Star Nightscape", and "Star Trails".  The latter mode is very similar to the "Live Composite" shooting mode offered by some Olympus (now OM-System) cameras.  

The Canon "Star Trails" mode does not offer much in terms of user-adjustable settings.  The exposure time from 10 minutes to 2 hr (in 10-min increments) and AF/MF are about the only choices.  For this test I set up the camera on a tripod pointing north, chose "60 min" for the exposure, pressed the shutter button, and walked away.

Crescent Venus

 At magnitude -4.6, Venus is the brightest object in the sky after the Sun and the Moon.  It is currently in its crescent phase, 22% illuminated.  The crescent phase is easlly observed with a small telescope.

These images were obtained during twilight at 6 pm on 20 Feb  while the planet was 32° above the horizon. The equipment used was a Celestron C6 SCT and an Olympus E-M5iii camera.  Exposure was 1/1600 sec at ISO 400. 

The best single image.

A stack of the three best images.

six-image animation.

This six-image animation shows the effect of atmospheric turbulence.  Dedicated planetary-photography practitioners will typically record a video consisting of hundreds (or more) frames, then select the sharpest fraction of that total to stack into a final image, with results that can be spectacular.  I am not a dedicated practitioner.

How far away is the Moon?

 Yesterday (12 Feb) was the February full moon, traditionally known as the "Snow Moon".  The clear sky provided an opportunity for a fun experiment: measure the distance to the moon.

The idea is simple.  Take a picture of the rising moon, and with the same equipment take another picture near midnight.  The moon will appear bigger at midnight because we are then closer by some fraction (depends on latitude) of the earth's radius.  If you know the radius of the earth, then the ratio of the two moon sizes and some simple math gives the distance to the moon.  The size of the earth was first measured in 240 BC by Eratosthenes, to an accuracy better than 1%.

The equipment used was an Astro-Tech AT72EDII f/6 refractor and field flattener with an Olympus E-M5iii camera.

The Snow Moon rising over the Sangre de Cristo mountain ridgeline.

It's hard to avoid utility lines when you live in the city.

Color balance adjusted to remove atmospheric color.

Approaching midnight (11:15 pm)

The moon near midnight was about 8 ± 1 pixels wider (1.4%) than the moon as it rose above the distant hills.  Taking into account the latitude of Santa Fe (35.7 deg) only, and ignoring the declination of the moon (12.3 deg),  the derived geocentric distance is L = 234,900 mi (378,00 km).   The ephemeris distance extracted from SkySafari was 242,028 mi (389,508 km).  This simple measurement therefore agrees with the known distance to within 3% (but with 13% uncertainty).

This technique could be improved by using a longer focal length scope to increase the pixel difference between the rising and transiting images.  Stacking images of the moon would also average out the blurring caused by atmospheric turbulence, particularly near the horizon.  But that's a lot more work, so yeah, I'm not going to do that.

Stars and planets putting on a show

The moon passed in front of the Pleiades star cluster on Wednesday night, 05 Feb.  That occultation did not begin until about midnight.  An image taken at 10:47 pm shows the moon approaching the cluster.

This was a 1-sec exposure at ISO 400 with a Nikon 180mm f/2.8 ED Ai-S lens.  This was a diffucult image to capture because of the large difference in brightness between the stars and the moon. Here is a version (ISO 1600) that shows more stars, but a vastly overexposed moon:

Jupiter is currently close to the Hyades Cluster:

Olympus 75mm f/1.8, Kase Astroblast filter.  ISO 400, 15 sec.

Aldebaran is a very red star, but it looks greenish (teal?) here, which is completely unnatural.  My best guess is that the diffusion filter is causing the longitudinal chromatic aberration (purple fringing) from the lens to be emphasized more than the saturated color at the core of the star image.  The deep blue sky from scattered moonlight may also be a factor.

Without the diffusion filter, two moons of Jupiter were resolved by the camera:

The two stars closest to Jupiter are the Galilean moons Callisto (left) and Ganymede (right).  The other two Galilean moons (Io and Europa) are lost in the glare of Jupiter.

Mars is making a bright triangle with Castor and Pollux in Gemini.

Olympus 75mm f/1.8.  Kase Astroblast filter.

The third star labeled in this image is Wasat, Delta Geminorum.  It is a nice double star for small telescopes.  The two components are magnitude 3.6 and 8.2, separated by 5.6 arcsec.  I was able to separate the pair photographically with the Celestron C6 and a 2.5x Powermate:

This image is a stack of eight exposures, 1/3 sec, ISO 1600.  A digital filter helps make the dim companion stand out better:

Crescent moon, distant planet

"Reach a hand to the crescent moon
Grab hold of the hollow
If she sits in the palm of the left
That moon will be fuller tomorrow"

Crescent Moon, Cowboy Junkies, 1993

I love the sight of a crescent moon setting over distant hills in the deep blue twilght.  This image (cropped and resized) is from 18 Oct 2020.  The moon was setting over the ridgeline of Bristol Head.  The camera was a Sony A7.  Based on the image scale, the lens was likely a Tokina 100-300mm f/4 AT-X SD zoom with a Nikon mount.  ISO 1600, 1/20 s.

After twilight faded, some more images were made to test a Nikon 180mm ED Ai-S lens.

 

This image was obtained with the Nikon 180mm lens and an Olympus E-P5 camera.  ISO 1600, 60 s.  It is hard to point a camera or telescope at the heart of the Milky Way without capturing multiple objects in the same view.  This image contains M8 (the Lagoon Nebula), M20 (the Trifid Nebula), the open cluster M21, and several other clusters.

M31.  E-P5 + Nikon 180mm f/2.8 Ai-S.  ISO 1600, 60 s.

The Andromeda Galaxy, M31, is a magnet for astrophotographers.  It is physically about twice the size of our Milky Way galaxy, and is also BIG in the sky.  The white circle in the above image represents the size of a full moon.

At one time, Pluto was known as the ninth and most distant planet.  That changed after the discovery of Eris in 2005, which led to the eventual reclassification of Pluto (and Eris) as a dwarf planet. Eris is slightly smaller than Pluto, but more massive (and much fainter, at magnitude 18.6+). Regardless of what it is called, Pluto is still there, and a challenge for both visual and photographic identification. 

Pluto, 18 Oct 2020 1-deg FOV.  Nikon 180mm, ISO 1600, 60 s.

 Pluto is at the center of the white circle in the above image.  At that time it was about magnitude 14.4.  The similar-brightness star just to its left is magnitude 14.2.  The faintest stars in this image are about magnitude 16.

A comet five years ago: C/2020 F3 (NEOWISE)

 I found this image from five years ago while looking for something completely unrelated.  In the first week of August 2020, Comet C/2020 F3 (NEOWISE) was fading in the western evening sky over the Bristol Head ridgeline near Creede. At the time this picture was taken it was passing in front of two globular clusters in the constellation Coma Berenices.  As a bonus, a meteor appeared in this 30 sec exposure.  

There is an immense range of distance scales in this image.  The meteor is an atmospheric phenomenon, probably within 100 mi or less.  The comet is a Solar-System object.  At that time it was about 86 million miles distant.  The globular clusters behind it are Galactic landmarks, about 58,000 light years distant.

Comet C/2020 F3. 06 Aug 2020.  Sony A7 + 50mm f/1.8 lens. ISO 1600, 30 s.

A tighter crop with the globular clusters circled.

That same evening I also took an image of the summer Milky Way, closely centered on the galactic core.  Same camera, lens, and exposure.

 With the distracting stars blurred, it is much easier to appreciate the immense clouds of dust and gas that obscure our visible-light view of the galactic center.