A Stellar Occultation by the Moon


Impending Occultation of Beta Capricorni

The double star Beta Capricorni disappears in a wink behind the Earthlit edge of the Moon.

The evening of Wednesday, November 26 provided a bonus celestial event, the eclipse of a double star by the Moon.

The star is Beta Capricorni, also known as Dabih. I had a ringside seat Wednesday night as the waxing Moon hid the star in what’s called an occultation.

Dabih is a wide double star, composed of a bright magnitude 3 main star, Beta1 Capricorni, and a fainter magnitude 6 companion, Beta 2 Capricorni. You can see both in the still image view at top. Their wide separation makes them easy to split in binoculars.

In reality, they are separated in space by an enormous gap of 21,000 times the distance from the Earth to the Sun. By comparison, distant Pluto lies an average of just 40 times the Earth-Sun distance.

With such a wide separation Beta1 and Beta2 take an estimated 700,000 years to orbit each other.

Beta1 is a giant orange star 600 times more luminous than our own Sun and 35 times bigger. Beta2 is a blue subgiant 40 times more luminous that the Sun.

Adding to the complexity of the system, Beta2 is also a close double, while Beta1 is a tight triple star, making for a quintuple star system.

The movie below records each occultation, first of the fainter blue Beta2 star, then of the brighter Beta1 star.

Each occultation happens in an instant to the eye. However, stepping through the video shows that the brighter star took 4 video frames to dim, about 1/10th of a second. Whether this is real, due to the star’s giant size, or just an effect of the twinkling of the atmosphere, is questionable.

Technical notes:

The still photo is a “high dynamic range” stack of 12 exposures from 4 seconds to 1/500th second, taken with the Canon 60Da camera at ISO 400, to capture the huge range in brightness, from the dark side of the Moon and stars, to the bright sunlit crescent. I used Photoshop’s HDR Pro module to stack the images and Adobe Camera Raw in 32-bit mode to do the tone-mapping, the process that compresses the brightness range into a final image.

I shot the video with the 60Da camera as well, setting it to ISO 6400, and using its video mode to record real-time video clips, both in HD 1920×1080 for the wide-field “establishing shots,” and in its unique 640×480 Movie Crop mode for the close-ups of the actual occultations. Those two clips appear as inset movies. I edited and processed the clips, plus added the titles, using Photoshop and its video capabilities.

All were shot from New Mexico with the TMB 92mm refractor at f/5.5.

– Alan, November 28, 2014 / © 2014 Alan Dyer

The Dark Side of the Moon in Twilight


Crescent Moon with Earthshine Amid Stars

The waxing crescent Moon shines amid the stars and deep blue twilight.

This was the scene last night, as the two-day-old Moon reappeared in the evening sky as a thin crescent.

The Moon looks full because most of the side facing us was brilliantly lit by Earthshine, sunlight reflected off the Earth and lighting the Moon. Here, only the thin crescent at right is directly lit by the Sun.

This was a particularly bright example of Earthshine, likely because so much of the northern part of the Earth is now covered with cloud and snow, making Earth even more reflective than it usually is.

To capture this scene through a telescope, I shot a set of high-dynamic-range exposures, from long to short, to capture the huge range in brightness from the dayside to the darkside of the Moon. The long exposure also captured the stars in the deep blue twilight of a clear New Mexico sky.

– Alan, November 25, 2014 / © 2014 Alan Dyer

Stargazing under the Milky Way


Stargazing at City of Rocks State Park

What a wonderful night for stargazing under the Milky Way and amid the rock formations of southern New Mexico.

This was the scene last night, November 22, at a monthly stargazing session hosted by the City of Rocks State Park and the local Silver City Astronomy Club. You couldn’t ask for a better night … and site.

The Milky Way swept overhead, from Sagittarius setting in the west at left, to Taurus rising in the east at right. The faint glow of Zodiacal Light sweeps up from the last glow of western twilight to the left. Some faint green bands of airglow that only the camera can capture are also visible near the horizon.

Matt is doing a laser tour, following which the group convened to the beautiful roll-off roof observatory that houses a Meade 14-inch telescope. It was a fine evening indeed.

Technical notes:

The panorama, which spans about 300° (I cropped the edges a little from the full 360°) consists of 8 segments, shot at 45° spacings, with a 15mm full-frame fish-eye lens at f/2.8, for 1 minute untracked exposures for each frame at ISO 800 with the Canon 6D. I stitched the segments in PTGui software, but processed them in Adobe Camera Raw and Photoshop.

– Alan, November 23, 2014 / © 2014 Alan Dyer

 

The Seven Sisters in a Silver Braid


M45 Pleiades Star Cluster, the Seven Sisters“Many a night I saw the Pleiads, rising thro’ the mellow shade,

Glitter like a swarm of fireflies tangled in a silver braid.”

– Alfred, Lord Tennyson

These are the famous Seven Sisters, the Pleiades, caught two nights ago in New Mexico skies. This bright star cluster stands out easily to the unaided eye in the winter sky, shining in the shoulder of Taurus.

What the eye does not see is the “silver braid” – the dim dust that surrounds the Pleiades. The stars light the dust, causing it to shine blue near the stars. Farther out, the dust is much dimmer and glows with pale tints of cyan and red.

The dust clouds were once thought to be what was leftover from the formation of the stars, now estimated to have occurred about 100 million years ago. However, current theory suggests that the natal dust of the Pleiads would have long since dispersed.

Instead, the silvery braids of dust that surround the Seven Sisters are just nearby dust clouds in Taurus that the stars are passing through, and illuminating with their hot blue light.

The Pleiades, as familiar as they are – they have been mentioned in ancient texts and myths dating back thousand of years – remain a source of scientific controversy. Astronomers argue over their distance, with different methods providing different results. But the best recent measurement puts them 440 light years away.

Technical notes: This is a stack of 10 x 12 minute exposures at ISO 400 with the Canon 5D MkII camera and 92mm TMB refractor at f/4.4. I shot the images November 16 from near Silver City, New Mexico.

– Alan, November 18, 2014 / © 2014 Alan Dyer

 

Both the Heart and Soul of Cassiopeia


Heart & Soul Nebulas (IC 1805 and IC 1848) in Cassiopeia

Here are both the heart and the soul of Cassiopeia the Queen.

Two days ago I posted an image of the Soul Nebula. Now, here is the matching Heart Nebula, in a mosaic of the glorious region of the Milky Way called the Heart and Soul Nebulas located in the constellation of Cassiopeia.

They are otherwise respectively called IC 1805 and IC 1848. Amid the swirls of nebulosity are numerous clusters of stars, such as NGC 1027 just above centre. The separate patch of nebulosity at upper right is NGC 896.

I shot the frames for this 3-segment mosaic over two nights, with one segment taken from the frames that made up the previous post. Plus I shot two others to span the region of the Milky Way that is about seven degrees long, a binocular field.

Each of the 3 segments is a stack of 12 frames, with each frame a 6-minute exposure. I used the filter-modified Canon 5D MkII and shot through the TMB 92mm apo refractor at f/4.4. All processing was in Photoshop, including the mosaic assembly.

In all, it’s the best image I’ve taken of this much-shot area of the sky. It really brings out the diversity in star colours, and sky colours, from the dusty orange-brown region at left, to the inky dark dustless region at far right.

– Alan, November 18 2014 / © 2014 Alan Dyer

 

The Soul of Cassiopeia


IC 1848, the Soul Nebula, in Cassiopeia

The Soul Nebula glows from within the constellation of Cassiopeia the Queen.

I shot this image last night, capturing an object prosaically known as IC 1848, but more popularly called the Soul Nebula.

It is often depicted framed with a companion nebula just “off camera” here to the right, called the Heart Nebula. Thus they are the Heart and Soul. Both shine on the eastern side of Cassiopeia the Queen.

Here I’m framing just the Soul, taking in some of the faint nebulosity to the left of the main nebula, including a tiny object called IC 289, a star-like planetary nebula at upper left.

I like this image for its variety of subtle colours, not only the reds and magentas in the bright nebula, but also in the dark sky around it from dim dust adding faint yellows, browns and even a touch of green.

The Soul Nebula lies 6,500 light years away in the Perseus Arm, the next spiral arm out from ours in the Milky Way. On northern autumn nights this region of the sky and Milky Way lies high overhead.

For the technically minded:

The image is a stack of 20 six-minute exposures, taken with a filter-modified Canon 5D Mark II at ISO 800. I was shooting through one of my favourite telescopes for deep-sky photography, the TMB (Thomas M. Back-designed) 92mm apo refractor, working at a fast f/4.4 using a Borg 0.85x field flattener and focal reducer.

I used one of Noel Carboni’s “Astronomy Tools” Photoshop actions to add the “diffraction spikes” on the stars. They are artificial (refractors don’t produce spikes on stars) but they add a photogenic touch to a rich starfield.

I shot this from the backyard of my New Mexico winter home.

– Alan, November 16, 2014 / © 2014 Alan Dyer

Truly Interstellar


M26 Open Cluster and NGC 6712 Globular Cluster

We gaze into the interstellar depths of the Milky Way through uncountable stars.

In this telescopic scene we look toward the Scutum Starcloud, and next spiral arm in from ours as we gaze toward the core of the Galaxy.

The field is packed with stars, seemingly crowded together in interstellar space. In fact, light years of empty space separate the stars, even in crowded regions of the Milky Way like this.

Two dense clusters of stars stand out like islands in the sea of stars. At lower right is Messier 26, an open cluster made of a few dozen stars. Our young Sun probably belonged to a similar family of stars billions of years ago. M26 lies 5,200 light years away.

At upper left is a condensed spot of light, made of hundreds of thousands of density packed stars in the globular cluster known only as NGC 6712. Though much larger and denser than M26, NGC 6712 appears as a tiny spot because of its remoteness – 23,000 light years away, a good part of the distance toward the centre of the Galaxy.

Look carefully (and it may not be visible on screen) and you might see a small green smudge to the left of NGC 6712. That’s a “planetary nebula” called IC 1295. It’s the blown off atmosphere of an aging Sun-like star. It’s what our Sun will become billions of years from now.

At top is a vivid orange-red star, S Scuti, a giant pulsating star nearing the end of its life.

A truly interstellar scene.

– Alan, November 9, 2014 / © 2014 Alan Dyer