Category Archives: Observing Log

Posts describing an observing session or astrophotography session.

M31 – Andromeda with Hubble’s Cepheid Variable V1 – 2017-01-15

The image below is a closeup of the Andromeda galaxy core. The area photographed includes the Cepheid variable star – M31_V1 – that Hubble used to calculate the first reliable distance to the “Andromeda Nebula”. His result proved conclusively that “nebula” were distant objects that were not part of the Milky Way.

M31 - Andromeda with Hubble V1 - 2017-01-15

M31 – Andromeda with Hubble V1 – 2017-01-15

The wide field view of Andromeda below shows the section of the galaxy captured in the close up image as well as locators for M31_V1.

M31 - Hubble V1 - Locator

M31 – Hubble V1 – Locator

Hubble used the recently commissioned 100″ Hooker telescope on top of Mount Wilson to capture a 1hr photographic plate of M31 on October 5/6, 1923. A crop from the original glass plate H335H (Hooker 335 Hubble) is shown below along with the same area from my image. Perhaps the plate has faded over the years or the technicians had keen eyes, but M31_V1 is barely visible.

M31_V1 Comparison - H335H with My M31

M31_V1 Comparison – H335H with My M31

Hubble had originally identified the star as a Super Nova and marked it “N”. Nova had been seen on plates before, so it was reasonable to assume that a star that had not been seen before was a super nova. However, reexamining previous plates and finding a fainter star in the same location, he then decided it was a variable star and marked it “VAR!”. This was significant because Henrietta Leavitt had earlier discovered a method for accurately calculating distances to Cepheid variable stars. Hubble’s discovery of M31_V1 was the first time a variable star had been observed in a nebula.

Cepheid variables are a class of variable stars that can be used as a “standard candle”. That is, their absolute (actual) brightness can be calculated, so their apparent brightness is then a measure of their distance (the dimmer the star, the further away it is). Today, Cepheid variables are still an important tool for determining distances to galaxies.

In 1908 Henrietta Swan Leavitt discovered a Period-Luminosity relationship for Cepheid variables that allows their absolute luminosity (brightness) to be calculated from their period – the time the star takes to vary from minimum to maximum intensity. At the time, she had been working for the Harvard College Observatory as a “computer” and assigned the task of identifying variable stars from photographic plates. Although the women computers were low paid and not even considered astronomers, they still made significant contributions to astronomy. She writes in her 1912 article defining the P-L relationship: “A remarkable relation between the brightness of these variables and the length of their periods will be noticed.

Prior to Leavitt’s ground breaking discovery, various techniques had been tried to determine the size of the Milky Way and the distance to M31 in particular, but none were conclusive. The prevailing view prior to Hubble’s measurement was that our Milky Way galaxy was about 30,000 light years in diameter (current estimates range from 100,000 to 180,000ly). And the Milky Way was the entire extent of the universe. The fuzzy objects visible in telescopes were described as “nebula” and thought to be within the boundaries of the Milky Way. There were some suggestions that these nebula lie on the periphery and could be as far away as 300,000ly, but the evidence was unconvincing.

Hubble’s H335H image was the first time a variable star had been identify in a “spiral nebula”, so this was the first opportunity to conclusively state the distance to M31. Hubble then took a series of plates to characterize the period and light curve of M31_V1 and confirmed it as a Cepheid variable. Using Leavitt’s P-L relationship rule and work Shapley had done to calibrate the rule to absolute distances, Hubble was able to calculate the distance to M31. He announced the results in a January 1925 paper presented to the American Astronomical Society stating definitively that M31 was 1,000,000ly away and clearly not contained within the Milky Way. (Current estimates put M31 at a distance of 2.5m light years.)

Hubble would then go on to locate variable stars in other nebula at even greater distances. Again he used Leaveitt’s P-L relationship to calculate the distances as well as the Doppler red-shift affect to determine their relative speeds. His observations showed that the further away a galaxy was, the faster it was receding from us. His now famous article in the 1929 Proceedings of the National Academy of Sciences declared for the first time that the universe was expanding!

And if it was expanding into the future, it must have been smaller in the past. This would eventually lead to the idea of the “Big Bang!”

Moon in Haze – 2016-10-16

I took this picture of the moon on a hazy, slightly foggy evening in October when the moon was one day past full.

Moon - 15-8days - In Haze - 2016-10-16

Moon – 15-8days – In Haze – 2016-10-16 (v2)

Taking a picture of the moon on a hazy evening proved to be quite challenging. To the naked eye, the moon looked much as it does on a clear night, albeit with a little less contrast. The halo surrounding the moon was bright but not overwhelming and had a tinge of colour. The pictures however were in stark contrast to what i had seen. A short exposure captured the contrast and detail on the moon’s disk but almost no halo. An exposure long enough to record the halo ended up with an overexposed moon.

Exposure Range - Normal Processing

Exposure Range – Normal Processing

I figured the problem was the dynamic range – the difference between the dark and bright areas was too large for the camera to capture. So i so decided to make a High Dynamic Range (HDR) composite from a range of exposures. But that didn’t really solve the problem either. The HDR image had enough range to capture both the halo and the bright moon without saturating or underexposing anything. But in order to get the halo bright enough to match what i saw, the moon details ended up looking washed out with almost no contrast.

I think the visual impression of being able to see both the halo and the moon details at the same time is just that – an impression. We might first take in the halo and then shift our focus to the moon’s disk to see the light and dark contrast on the surface. In our mind’s eye we integrate the two views which leaves us with the impression of seeing both the halo and the disk at the same time.

I ended up using masks to artificially darkening the moon’s surface in the HDR image in order to show both the halo and the moon details. The HDR image had all the resolution and range to show as much moon surface detail as i wanted, but when overdone, it looked like i just pasted a copy of some other moon shot on top of the halo. So i had to limit this technique in order to keep things looking natural. Which left the moon’s surface still looking a little washed out and the halo not quite as bright as it appeared to the naked eye.

Processing Details

Of the many different exposures, 10 images were selected for the HDR composite with a range of about 2-1/2 stops and a relatively smooth increment in exposure value (EV) between images.

Non-linear vs Linear

The normal processing of the raw sensor data applies a strong non-linear transformation to the otherwise linear sensor pixel values – sometimes referred to as the Digital Development Process (DDP). This reflects how our eyes perceive brightness and results in a “normal” looking image. The camera does this when creating a JPG and also what the Canon DPP tool does by default when displaying a RAW file or creating a JPG or TIFF file. For an image with a wide dynamic range to start with, this non-linear transformation tends to blow out the brighter areas of the scene or under-expose endarker areas. The darker areas are less affected due to the nature of the non-linear transformation.

The screen shot below is for an exposure in the middle range of the 10 selected for the HDR composite. It shows the default (non-linear) processing that DDP uses for a raw CR2 file. With the normal processing, all but the darkest area of the moon’s surface appears saturated.

Normal Processing - 1x50s, f/5.0

Normal Processing – 1x50s, f/5.0

The next screen shot is the same image as above, but with the “Linear” option selected in DPP. All of the darker areas of the moon’s disk are now in range and visible. There is still some saturation of the brighter areas but this is expected since this is the mid-range EV of the set. The HDR integration process will use pixel data from the shorter, less saturated images to fill in areas of the brighter images.

Linear Processing, 1x50s. f/5.0

Linear Processing, 1x50s. f/5.0

Note that although the halo isn’t visible in the linear image. It’s still the same data as the saturated DPP image and therefore still there. So the levels can be adjusted later to bring back this detail just as the non-linear (DDP) stretch brought out the halo. But now this can be done selectively.

I figure the linear version recovers about 2 stops of range over the non-linear version. So the 2-1/2 stops in normal processing becomes 4-1/2 stops in linear mode.

HDR Process

The 10 CR2 files were converted to linear mode 16bit TIFF files and loaded into Photoshop CS5 as layers in a single PSD file.  The PS auto-align feature wouldn’t align the images, so each layer was aligned manually.

Aligning lunar images is actually quite easy to do with PS. The layer to align is placed above the reference frame. Then the upper layer opacity is set to 50% and inverted to make it obvious which layer is which. Using the selection tool (arrow) the layer can be nudged into place. When the layers are exactly aligned, the two layers more of less cancel each other out and turn neutral grey. Correcting for rotation errors is a little more tedious but doable. Manual alignment doesn’t do sub-pixel adjustments but it’s ok for this type of work.

The image below shows the 10 images used for the HDR composite aligned and sorted by exposure values (slightly stretched to better show the range and increments):

HDR Exposure Value Set

HDR Exposure Value Set

PS CS5 actually has 2 HDR tools – neither of which produced anything close to being useful. PixInsight also has an HDR Integration tool and it produced a reasonable result. But the tool could not be coerced into including a significant halo from the lonager exposures. And the HDR integration looked very artificial and was difficult to corrected post merge.

So the only option left was a manual merge using PS layers and masks. The layers were stacked in increasing EV.

HDR Layers with Masks

HDR Layers with Masks

A mask was applied to each layer using a range mask to exclude the saturated areas. Then each mask was adjust using levels to increase the contrast. Initially the opacity of each layer was set to give each layer equal weight. (The strange but true formula for determining the percentage for each layer is : opacity = 100 / layerNumber. So setting the 2nd layer opacity to 50% and the 3rd layer to 33% gives the layers equal weight for blending.)

It turned out that equal weights didn’t allow enough of the brighter pixels from the longer exposures to contribute to the blended image. So the opacity was set to 100% for all layers and the blending left mostly to the masks.

With the HDR blending done, levels and curves were used to brighten the image. Later, a mask was used to allow the halo to be brightened while leaving the moon’s disk untouched.

Vega and the Constellation Lyra – 2015-10-30

The bright star Vega at magnitude 0.03 is the 5th brightest star in the sky and the third brightest star visible from the 45th parallel (Ottawa). Sirius at magnitude -1.46 is the brightest star in the sky and Arcturus magnitude -0.05 is the second brightest in the north. Although the yellow-orange star Arcturus is only marginally brighter than Vega, Vega has the advantage of being near the zenith on summer nights and the slight blue tint makes it seem even brighter.

Vega Closeup - 2015-10-30

Vega Closeup – 2015-10-30

Vega is in the constellation Lyra – the lyre or harp. Lyra is one of 48 constellations listed by Ptolemy in the second century and is on the International Astronomical Union’s (IAU) official list of 88 constellations. The long exposure image below shows the 4 bright stars of the harp as well as Epsilon Lyra (ε1, ε2 – the Double Double) left of Vega and Kappa Lyra (κ) to the right.

Vega in the Constellation Lyra - 2015-10-30

Vega in the Constellation Lyra – 2015-10-30

The chart overlay below  shows the location of the bright stars as well as the location of the M57 Ring Nebula. Vega is 25ly from earth while the other stars are at various distances. So the lyre shape is just a chance alignment when viewed from earth.

  • Vega: mag 0.03, dist 25ly
  • Epsilon 1: mag 4.65, dist 162 ly
  • Epsilon 2: mag 4.56, dist 161ly
  • Kappa: mag 4.31, dist 238ly
  • Zeta: mag 4.31, dist 154ly
  • Delta: mag 4.21, 906ly
  • Sheliak: mag 3.50, 882ly
  • Sulafat: mag 3.25, 640ly
Lyra Constellation Stick Figure

Lyra Constellation Stick Figure

The next image is modified to reduce the fainter stars and is more representative of what the sky might look like from a dark site. With this image, the bright stars of the constellation Lyra are more obvious.

Vega in the constellation Lyra - Less Stars -2015-10-30

Vega in the constellation Lyra – Less Stars -2015-10-30

While we think of constellations as the stick figure above or the elaborate drawings of mythical figures, the IAU defines a constellation as a non-overlapping region. So Lyra extends a little past the obvious 7 bright stars and defines a region in the sky between Cygnus to the east and Hercules to the west.

Lyra Constellation Boundaries

Lyra Constellation Boundaries

Lyra is home to a few interesting night sky objects:

Within the “stick figure” there are:

  • Epsilon – the double double
  • Messier 57 – The Ring Nebula
  • Zeta, Delta and Sulafat are doubles

Within the boundaries there are also:

  • M56 – an 8.3 magnitude globular cluster with an apparent size of 5arc-minutes
  • NGC 6791 – an 9th magnitude open cluster spanning 19′

The pair of stars Epsilon Lyra 1 and 2 (ε1, ε2)  are gravitationally bound to each other – meaning they are in the same region and rotate around each other (although in thousands of years). Each of ε1, ε2 is also a pair of stars that can be seen as doubles though a medium to large telescope. ε1, ε2 have a separation of 3.5′ which can be seen in binoculars. The doubles of ε1, ε2 each have separations of 1.3″ and 2.3″ making them challenging doubles to split in a 4″ scope. However, the two pairs are oriented 90° with respect to each other making it easy to compare the star shapes and aiding in detecting the separation. The periods of each pair are in the range of 600 to 1200 years. The finder chart below helps when trying to “split” the doubles.Finder_Chart_Epsilon-Lyra

The image below of the double-double doesn’t quite manage to show a gap between the close pairs. This is what might be typically seen in a smaller scope or a night of poor seeing. Still, by noticing that each pair is actually oval shape, the direction at least of the doubles gives a clue that they are doubles.

DoubleDouble_Epsilon_Lyra_2008-06-10_v1_SJM

Messier 57 (NGC6720) – the Ring Nebula is a large bright planetary nebula. Its visual magnitude is 9.5 and 3 arc-min across. On good nights and a large telescope, the remnants of the central star that exploded is visible. The ring is the expanding cloud of hot gas thrown off when the star shed its outer shell. The image below easily captures this detail as well as the colour which is not discernible through the eyepiece.

M57 - Ring_Nebula - 2011-07-30 - v2

M57 – Ring_Nebula – 2011-07-30 – v2

Vega rises during the late evening in April. It will be low in the north-east at about 9:30pm edt mid-April and makes its way across the sky during the night. By midnight it’s still in the north-east and only 25° above the horizon. It doesn’t transit (crosses due south) until 6am though!

Of course, if one is willing go out at much later times, Vega is also visible in the winter but after midnight. I tend think in terms of what objects are visible during normal evening hours.

Lyra Finder Chart - Sky facing East on 2015-04-15 at 21:30hrs EDT

Lyra Finder Chart – Sky facing East on 2015-04-15 at 21:30hrs EDT

Each month Vega rises two hours earlier. Which means it transits two hours earlier each month. By late summer at 9:30pm edt, Vega is due south and high in the sky near the zenith. The chart below shows Vega and Lyra high in the sky due south nestled between Pegasus and Hercules.

Lyra Finder Chart - Sky facing South on 2015-09-01 at 21-30hrs EDT

Lyra Finder Chart – Sky facing South on 2015-09-01 at 21-30hrs EDT

By December, Vega is low in the west in the evening and soon will disappear altogether from the evening sky.

Lyra Finder Chart - Sky facing East on 2015-04-15 at 21:30hrs EDT

Lyra Finder Chart – Sky facing East on 2015-04-15 at 21:30hrs EDTj

But … as said earlier, if one wanted to go out at other times, Vega can still be seen during winter. Starting in December, Vega is also visible in the early morning sky! The chart below shows Vega rising at 6:30 am (when it’s still dark in Ottawa) the day after it set in the west on the evening before.

Lyra Finder Chart - Sky facing East on 2015-12-16 at 06-30hrs EST

Lyra Finder Chart – Sky facing East on 2015-12-16 at 06-30hrs EST

Each month Vega will rise 2hrs earlier. So in January it rises at 4:30am and in February it rises at 2:30. By April it will be rising at 9:30 again.

So Vega is actual visible all year long, but to see it might mean going outside to look for it while sleeping is a better alternative.

 

 

 

 

 

Lunar Eclipse – 2015-09-27

The weather reports of the preceding days and even the day of the eclipse predicted clear skies. So i planned a photography project to create a time lapse sequence covering the entire event from penumbra advance, through total eclipse and then the receding shadow.

As it turns out, the clouds moved in about the time the eclipse started. By the time the umbra shadow started, there was a significant risk of total overcast. The clouds did manage to behave themselves for most of the waxing eclipse, but just before full eclipse the cloud cover was 100%.

I was using the Canon XS (filter removed) with the AstroTech 106 (AT106) mounted on the Skywatcher EQ5-Pro. The plan was to take images every 20sec for the duration of the event. To reduce disk space i choose the “S” setting of 1936×1288 pixels as having adequate resolution for a movie. Not having done this before, i was not prepared for the changes required in exposure settings. I started with ISO 400 and 1/2000s exposures (the scope is f/6.5). I had expected to adjust the EV (exposure value) as time went on to account for the diminished light of the eclipsing moon, but was not prepared the problems caused by the clouds.

The intermittent cloud cover exacerbated the changes to EV making it somewhat unexpected if not random. This and required dramatic changes to the TV time during periods of partial cover resulted in widely varied exposure values. I ended up with frames that were too dark as well as too bright. And whole sequences that differed substantially from the previous frames.

Because of the location require to get a clear view of the entire eclipse, it was not possible to pre-align the scope. So i also had to contend with Polar Alignment  drift between frames. This required minute by minute adjustments to the framing to keep the moon more or less in the centre of the frame. I was hoping for some auto-alignment tools to refine this during post-processing (more later).

The cloud cover was 100% a few minutes before full eclipse. I decided to abandon the time lapse project in favour of getting a high resolution RAW file of the mostly eclipsed moon. I managed only one full resolution image before the clouds covered up everything, I also choose ISO 1600, which is quite noisy on the XS with only 1/10s exposure. Lower ISO and longer exposure would have provided a cleaner image.

Lunar Eclipse 2015-09-27

Lunar Eclipse 2015-09-27

I did mange to grab 360 frames at the lower resolution to create a time lapse sequence of the event. I could not find a tool to accurately align the  images, so i manually aligned them with the Canon DPP tool. This allows alignment to the pixel level, which is adequate, but still not quite good enough. I also had to manually adjust the EV levels for groups of images as well as individual images. The resulting movie is at best interesting but not quite the epic i had planned.

The video covers the time period from 8:04pm to 10:06pm EDT. The penumbra shadow started at 8:12 with the umbra starting at 9:07. Full eclipse started at 10:11. It takes quite awhile before the penumbra is evident.

The video compresses the 122 min lapsed time into 36 seconds. So each second of video is about 3 1/2 min of real time.

Hornets -2015-09-08

I opened up the observatory this evening for a quick test of some upgraded software and a mini-guider using a finder scope. I did a quick scan of the roof before opening it to check for bugs – wasp and hornets in particular. I didn’t find anything untoward so i opened up the roof and went to work.

As there were a few misquotes and black flies, even this late in the summer, i started the Thermocell. Good thing as it it turned out.

About a half an hour into the project a large bug crawled across the laptop screen. I thought it was a medium sized spider – which i am needless to say, not too fond of. I switched on the white light light to get a better look and found not a spider, but a large hornet! Looking up, i then saw the hornets nest on the side of the dome wall and about 18″ from my nose!

I made a hasty retreat to a comfortable distance and perused the situation. The nest was small but active. It was only about 3″ by 6″ but there were a dozen or more hornets crawling around it and many more near by. They were however rather docile for hornets which i attribute to the Thermocell.

I gingerly shutdown the laptop and closed the cover of the cupboard it’s housed in. I shutdown the mount without bothering to return it to home or even hibernate. Then i went to the garage and fetched a hornet blaster. I soaked the nest and targeted several stray hornets. In the morning there were still many live hornets to be dealt with.

More frightening than realizing the nest was basically in my face, was the thought that i nearly put hand in the nest. The observatory is a skyshed pod. The half roof opens and then the open half dome is rotated around to face the sky being observed. To move the dome i just push on one of the supports which was only inches from the nest. Had the nest been located nearer to the support, i would have put my hand directly onto the nest. Yikes!

Hornets are gone and i think i will check the observatory in daylight more frequently.

Abell 1656 – Coma Cluster – 2015-05-18

Coma Cluster (Abell 1656)
Imaged 2015-05-18

The Coma Cluster is a large cluster of galaxies that contains over 1,000 identified galaxies. Th image below shows a just a few hundred. The magnitudes of the ten brightest galaxies are between 12–14. The two largest galaxies at the centre are supergiant elliptical galaxies: NGC 4874 and NGC 4889. The Coma Cluster is part of the Coma Supercluster.

Abell 1656 - Coma Cluster - crop - 2015-05-18

Abell 1656 – Coma Cluster – crop – 2015-05-18

As its name implies, the cluster is located in the direction of the constellation Coma Berenices. While the three bright stars in the constellation are between 28 Mly and 167 Mly from us, the Coma Cluster of Galaxies is 321 Million lights years away.

The North Galactic Pole is located in Coma Berenices. So looking towards Coma Berenices is then looking up from the galactic plane and therefore there are fewer stars than when looking through the plane.

The Coma Cluster is one of the first places where dark matter began to be suspected. In 1933 Fritz Zwicky showed that the galaxies of the Coma Cluster were moving too fast for the cluster to be bound together by the visible matter of its galaxies. It is now thought that about 90% of the mass of the Coma cluster is dark matter.

Image details:
AT106 with AT2FF
Canon T2i (Astronomy UV/IR filter mods)
– 17 x 600sec frames at ISO1600 (total integration time 2hr 50m
CGE Pro
Guided with Shorttube 80 and Chameleon
Metaguide with FlexRX
Image capture with Backyard EOS
Calibrated, stacked and processed with PixInsight
Cropped, original pixel scale

M96 Group in Leo – 2015-04-14

M96 Group in Leo (the Leo I Group)
acquired 2015-04-14

The image below shows 5 of the 8 brightest galaxies in the M96 group. There are estimated to be as many as 24 galaxies in the group, all of which are in the same general vicinity and gravitationally bound to each other.

M96 Group - 2015-04-17

M96 Group – 2015-04-17

From left to right:

NGC 3384
– Mag 10.9
– Size 5.5′ x 2.5′
– Distance     35.1 Mly
M105 (NGC 3379)
– Mag: 10.2
– Size: 5.4′ x 4.8′
– Distance: 32 Mly
NGC 3389/3373 (Below NGC 3384)
– Mag: 11.2
– Size: 2.7′ x 1.2′
– Distance: ?
M96 (NGC 3368)
– Mag : 10.1
– Size: 7.6′ x 5.2′
– Distance: 31 Mly
M95 (NGC 3351)
– Mag: 11.4
– Size: 3.1″ x 2.9′
– Distance: 32.6 Mly

There are few other faint fuzzies that may not be part of the group. While visually in the field of view, they are either closer or further away from the M96 cluster of galaxies.

Taken 2015-04-18
AT106 with A2FF
Canon T2i (astrodon UV/IR inside)
14 x 360s @ISO1600 (another 28 subs had lost the guiding)
– total integration 1hr, 24min
CGE Pro guided with Shorttube80 and Chameleon
– Metaguide with FlexRX
Captyured with Backyard EOS
Calibrated, Stacked and Processed with PixInsight
Full Frame, original pixel size.

Eskimo Nebula – 2015-03-23

Eskimo (Clown) Nebula (NGC 2392, Caldwell 39)
Taken 2015-03-23, 21:00 to 23:30edt

Eskimo Nebula - Full Frame - 2015-03-23

Eskimo Nebula – Full Frame – 2015-03-23

This is a planetary nebula called the Eskimo Nebula or sometimes Clown Face Nebula. Planetary nebulas get their name because they appeared to early telescope observers like giant planets. They are actually an expanding shell of ionized gas ejected from a catastrophic event in the late stages of medium to small star’s life. (Contrast this to supernova for giant stars.) The Eskimo nebula actually has two shells of expanding gas which gives it an unusual appearance.

Distance 3000 light years
Apparent mag 9.1
Central star mag 10.5
Visual Size 48 x 48 arc-sec

A closer crop and up-sampled 2x is easier to look at, but does not show any more detail:

Eskimo Nebula - - Crop - 2015-03-23

Eskimo Nebula – – Crop – 2015-03-23

Celestron HD11
Canon T2i with Astrondon uv/ir filter inside
Guided with Celstron OAG, Chameleon and Metaguide

HDR at ISO1600
– – 15 x 120s
– – 7 x 180s
– – 18 x 240s
– total integration 2hrs

Venus and Mercury – 2015-05-06

Mercury

Mercury was at its greatest elongation for 2015 om May 6th at 21deg, so i decided to try to capture an image of it. Being low in the sky it’s hard to get a clear view through the murky unstable surface air. So i decided to capture the image just after sunset at 20:19edt when it was still relatively high. Mercury was not yet visible unaided, but it showed up well in the telescope. The sun had just set at 20:16 when i captured the image, so it was only 0.5deg below the horizon. Nautical dusk wasn’t until 21:31. The down side was the bright evening sky reduced contrast. Given it’s very difficult or unusual to resolve any surface details of Mercury in a backyard telescope, the lack of contrast wasn’t going to matter.

Mercury 2015-05-06, 20-19edt

Mercury 2015-05-06, 20-19edt, Monochrome

Being only 7.9″ in angular size, it is very difficult to resolve any surface details at the best of times. And being so low in the sky and taken only minutes after sunset, the unstable surface air and low contrast obscured what details might be obtainable. The only interesting feature then is the phase. Mercury is also grey, like the moon, so a colour image wouldn’t actually have any colour.

I used the Celestron HD11 with a 5x Powermate. The effective focal length is therefore 14,000mm at effectively f/50. I capture a 60sec AVI (movie) at a resolution of 640×480 at 30fps with a monochrome Point Grey Chameleon (no filters). That works out to 1792 frames. Using Autostakkert2, i selected the best 10% of the frames and stacked them into a single image. Further processing with PixInsight (wavelets and curves) sharpened up the edges to reveal a nice waxing crescent – but no surface detail.

The specs for Mercury that evening were:

  • Mag: +0.4
  • Size: 7.9 arcsec
  • Illumination: 38%
  • Azimuth: 286deg
  • Altitude: 18deg
  • Elongation from Sun: 21deg (at maximum)

I tried using a 35nm IR pass filter with the above setup, but at f/50, there wasn’t enough light. The advantage of using IR is it less affected by the turbulent air and the narrow bandwidth improves focus. A future project is to try the IR filter with the HD11 at prime focal length or with a 2x powermate.

Venus

Venus was at a greater elongation [from the sun] so i waited until 21:04edt to capture that image. The sun was now 7.5deg below the horizon and closer to nautical dusk (21:31).

Using the same technique above, i captured two 60sec AVIs and processed them with the same method. Then i combined the two resulting images which reduced some blotches.

Venus 2015-05-06, 21:04edt

Venus 2015-05-06, 21:04edt, Monochome

Venus is blanketed by a thick white cloud, but unlike Jupiter and Saturn, there is no colour or banding visible in white light. (I have seen some images in UV that do show some some cloud details.) So even though Venus is a reasonable 18arcsec in angular size, the only interesting feature is the phase.

The specs for Venus that evening were:

  • Mag: -4.14
  • Size: 18 arcsec
  • Illumination: 64%
  • Azimuth: 280deg
  • Altitude: 28deg
  • Elongation from Sun: 43deg (maximum is 45deg)

Venus and Mercury Comparison

Since i had the two images created with the same gear, i decided to display them side by side to show the relative angular sizes:

Venus and Mercury 2015-05-06

Venus and Mercury 2015-05-06

 

Examples of What Other People Can Do

While it’s difficult to get images that show any detail on either Mercury or Venus, it is possible to capture images using relatively modest ground based equipment (not billion dollar mountain top scope). The links below to Daniele Gasparri’s web site [external link] show some impressive images that have been acquired using a C14 combined with various filters.


Mercury by Daniele Gasparri [External Link}


Venus by Daniele Gasparri [External Link}

Micro Moon – 2015-03-05

To complement the “Super” moon of September 9th, 2014, the moon was at it smallest for 2015 on March 5th. The conditions were almost just as good as in September 2014, so i managed to capture a view of the apogee full moon (furthest away) that was almost indistinguishable from the Super moon expect that it was 10% smaller.

Micro Moon - 15.14days - 2015-03-05

Micro Moon – 15.14days – 2015-03-05