Monthly Archives: May 2014

Sequence of the occultation of Saturn by the Moon

DP ENGLISH: This story belongs to the series “Double Post” which indicates posts that have been written both in English in The Lined Wolf and in Spanish in El Lobo Rayado.

DP ESPAÑOL: Esta historia entra en la categoría “Doble Post” donde indico artículos que han sido escritos tanto en español en El Lobo Rayado como en inglés en The Lined Wolf.

Today Sunday I’ve used some of my free time to process the images I took last Wednesday, when Saturn was occulted by an almost full Moon. These are my two final images showing how Saturn first disappears behind the Moon and it reappears an hour later.

The Moon occults Saturn I: Saturn disappears.
14 May 2014 from Sydney. Data obtained using Telescope Skywatcher Black Diamond D = 80 mm, f = 600 mm, 20 mm eyepiece + CANON EOS 600D. All times are given in Universal Time, add 10 hours to get the local time in Sydney (AEST) that date. Images of Saturn obtained combining many frames at 1/60 and 1600 ISO using Lynkeos software + Photoshop. Image of the Moon obtained combining 20 best frames using Photoshop. Credit: Á.R.L-S. (AAO/MQ)


The Moon occults Saturn I: Saturn disappears.
14 May 2014 from Sydney. Data obtained using Telescope Skywatcher Black Diamond D = 80 mm, f = 600 mm, 20 mm eyepiece + CANON EOS 600D. All times are given in Universal Time, add 10 hours to get the local time in Sydney (AEST) that date. Images of Saturn obtained combining many frames at 1/100 and 1600 ISO using Lynkeos software + Photoshop. Image of the Moon obtained combining 11 best frames using Photoshop. Credit: Á.R.L-S. (AAO/MQ)

Getting nice images of Saturn was much trickier than I expected: the setup I used the other night it is not the best to observe Saturn, as more magnification and a good tracking are needed. On the other hand, the Moon was very bright so I had to use short exposition times, and hence Saturn appeared very dim. At the end I manage to get a kind of “master Saturn” combining the best frames I took during the night and later combine it with the data of each position to get the final view of Saturn at each time. For the Moon it was much easier, although you’ll perhaps realize that the second image is somewhat better than the first. The reason is that some parts of the Moon were actually saturated with the 1/60 seconds exposures, and that is why I later used 1/100 seconds for getting Saturn reappearing. In any case, I hope you like them.

Occultation of Saturn by the Moon

Today, 14th May 2014, Saturn is occulted by the Moon, although this can only be seen from most Australia and New Zealand. I’ve set up my telescope in the backyard and now I’m taking some photos of the event. Although I’ll try to get better images later, let me show you what I’m obtaining now.

These three images show how Saturn is moving closer to the Moon:

Occultation of Saturn by the Moon, as observed from my backyard in Sydney. I used my Skywatcher Black Diamond Telescope D = 80 mm, f = 600 mm and my CANON EOS 600D, and a 20mm eyepiece projection, at 1600 ISO and speed 1/60. This is just a single frame obtained at 20:44 AEST (10:44 UT). I also used Photoshop to play with the levels/colours/saturation. Credit: Angel R. López-Sánchez.

Occultation of Saturn by the Moon, as observed from my backyard in Sydney. I used my Skywatcher Black Diamond Telescope D = 80 mm, f = 600 mm and my CANON EOS 600D, and a 20mm eyepiece projection, at 1600 ISO and speed 1/60. This is just a single frame obtained at 21:12 AEST (11:12 UT). I also used Photoshop to play with the levels/colours/saturation. Credit: Angel R. López-Sánchez.

Occultation of Saturn by the Moon, as observed from my backyard in Sydney. I used my Skywatcher Black Diamond Telescope D = 80 mm, f = 600 mm and my CANON EOS 600D, and a 20mm eyepiece projection, at 1600 ISO and speed 1/60. This is just a single frame obtained at 21:18 AEST (11:18 UT), the planet is “touching” the disc of the Moon. I also used Photoshop to play with the levels/colours/saturation. Credit: Angel R. López-Sánchez.

After that, I waited for 40 minutes to see Saturn reappears behind the Moon, as it is shown is the next three photos:

Occultation of Saturn by the Moon, as observed from my backyard in Sydney. I used my Skywatcher Black Diamond Telescope D = 80 mm, f = 600 mm and my CANON EOS 600D, and a 20mm eyepiece projection, at 1600 ISO and speed 1/100. This is just a single frame obtained at 21:59 AEST (11:59 UT). I also used Photoshop to play with the levels/colours/saturation. Credit: Angel R. López-Sánchez.

Occultation of Saturn by the Moon, as observed from my backyard in Sydney. I used my Skywatcher Black Diamond Telescope D = 80 mm, f = 600 mm and my CANON EOS 600D, and a 20mm eyepiece projection, at 1600 ISO and speed 1/100. This is just a single frame obtained at 22:05 AEST (12:05 UT). I also used Photoshop to play with the levels/colours/saturation. Credit: Angel R. López-Sánchez.

Occultation of Saturn by the Moon, as observed from my backyard in Sydney. I used my Skywatcher Black Diamond Telescope D = 80 mm, f = 600 mm and my CANON EOS 600D, and a 20mm eyepiece projection, at 1600 ISO and speed 1/100. This is just a single frame obtained at 22:15 AEST (12:15 UT). I also used Photoshop to play with the levels/colours/saturation. Credit: Angel R. López-Sánchez.

In the next few days I’ll prepare some few better (processed) images. Stay tuned!

A 2dF night at the Anglo-Australian Telescope

One of the most complex astronomical instruments nowadays available is the Two Degree Field (2dF) system at the Anglo-Australian Telescope (AAT, Siding Spring Observatory, NSW, Australia). The main part of 2dF is a robot gantry which allows to position up to 400 optical fibers in any object anywhere within a “two degree field” of the sky.

The 2dF instrument attached to the primary focus of the AAT. Note that the mirror of the telescope is opened. This image was chosen to be part of the Stories from Siding Spring Observatory Photo Exhibition the AAO organized last year.
Credit: Á.R.L-S.

392 optical fibers are fed to the AAOmega spectrograph, which allows to obtain the full optical spectrum of every object targeted by an optical fiber. The remaining 8 optical fibers are actually fibre-bundles and are used to get an accurate tracking of the telescope while astronomers are observing that field, which may last up to 3 hours. 2dF possesses two field plates: one located at the primary focus of the telescope and another at the position of the robot gantry. While a field is being observed in one plate, 2dF configures the next field on the other plate. A tumbling mechanism is used to exchange the plates. 2dF was designed at the AAO in the late 90s and, since then, it has been used by a large number of international astrophysicists. In a clear night, 2dF can obtain high-quality optical spectroscopic data of more than 2,800 objects.

Indeed, this sophisticated instrument has conducted observations for hundreds of astronomical projects, including galaxy surveys such as the 2dF Galaxy Redshift Survey, the WiggleZ Dark Energy Survey, and the Galaxy And Mass Assembly (GAMA), survey which is still on going and in which I actively participate. The optical fibers of 2dF can be also fed the new HERMES spectrograph, which is now starting the ambitious Galactic Archaeology with HERMES (GALAH) survey at the AAT. GALAH aims to observe around 1 million galactic stars to measure elemental abundances and measure stellar kinematics.

Frame of the time-lapse video “A 2dF night at the Anglo-Australian Telescope”. The 2dF robot gantry moving and positioning the optical fibers. Credit: Á.R.L-S.

How does 2dF move and position the optical fibers? A very nice way of explain it is using the time-lapse technique, that is, taking many images and then adding all to get a movie of the robot while moving and positioning the fibers. That is why in 2012 I decided to create the video, A 2dF night at the AAT, which assembles 14 time-lapse sequences taken at the AAT during September and November 2011 while I was working at the AAT as support astronomer of the 2dF instrument. Actually, this time-lapse video shows not only how 2dF works but also how the AAT and the dome move and the beauty of the Southern Sky in spring and summer. The time-lapse lasts for 2.9 minutes and combines more than 4000 frames obtained using a CANON EOS 600D provided with a 10-20mm wide-angle lens.

Time-lapse video “A 2dF night at the AAT”. I recommend to follow the link to YouTube and watch it at HD and full screen in a dark room. Credit: Á.R.L-S.

The video consists in three kinds of sequences created at 24 frames per second (fps). The first 3 sequences show how the 2dF robot gantry moves the optical fibers over a plate located at the primary focus of the telescope. Although in real life 2dF needs around 40-45 minutes to configure a full field with 400 fibers, the time-lapse technique allows to speed this process. The first 2 sequences have been assembled taking 1 exposure per second, therefore 1 second of the video corresponds to 24 seconds in real life. The third sequence considers an exposure each 3 seconds, and hence it shows the robot moving very quickly. The next four sequences show the movement of the telescope and the dome. All of them were obtained taking 2 images per second (a second in the movie corresponds to 12 seconds in real life). The long black tube located at the primary focus of the telescope is 2dF. The remaining sequences, all obtained during the night, were created taking exposures of 30 seconds, and hence each second in the video corresponds to 12 minutes in real life.

Frame of the time-lapse video “A 2dF night at the Anglo-Australian Telescope”. The AAT telescope, with 2dF (the long, black tube) attached at its primary focus, is prepared to start observing. Credit: Á.R.L-S.

Astronomical time-lapse videos allow to see the movement of the Moon, planets and stars in a particular position in the Earth, something that conventional videos cannot achieve. In particular, dim stars and faint sky features, such as the Milky Way with its bright and dark clouds and the Magellanic Clouds, can be now easily recorded. As in my first time-lapse video, The Sky over the AAT, I set the camera up at the beginning of the night, let it run, and check on its progress occasionally. I used at focal of f5.6 and an ISO speed of 1600 ISO for the night sequences.

Frame of the time-lapse video “A 2dF night at the Anglo-Australian Telescope”. The Magellanic Cloud rise while the Milky Way sets over the Anglo-Australian Telescope at Siding Spring Observatory on 3 Nov 2011. Some kangaroos can be seen in the ground. Credit: Á.R.L-S.

However, the procedure that took more time was processing the hundreds of individual photographies included in each sequence. In many cases, I needed more than 12 hours of computer time, including 3 or 4 iterations per sequence, to get a good combination of low noise and details of the sky, plus “cleaning” bad pixels or cosmic rays. In particular, for this video I tried hard to show the colours of the stars, a detail which is usually lost when increasing the contrast to reveal the faintest stars. In the last sequence of the video, Aldebaran and Betelgeuse appear clearly red, while the stars in the Pleiades and Rigel have a blue color.

Frame of the time-lapse video “A 2dF night at the Anglo-Australian Telescope”. A dark night at The Anglo-Australian Telescope (23 Sep 2011). Orion constellation is seen over the AAT dome. The red colour of Alderaban and Betelgeuse and blue colours of Pleiades and Rigel are clearly distinguished. Credit: Á.R.L-S.

As I did for my previous time-lapse, here I also included a sequence which shows the trails created by the stars as they move in the sky as a consequence of the rotation of the Earth. This sequence shows the Celestial Equator and stars at the South (top) and North (bottom) Celestial Hemisphere. Note that star trails have indeed many different colours. Other details that appear in this time-lapse video are clouds moving over the AAT, satellites and airplanes crossing the sky, the nebular emission of the Orion and Carina nebulae, the moonlight entering in the AAT dome, and kangaroos “jumping” in the ground.

Frame of the time-lapse video “A 2dF night at the Anglo-Australian Telescope”. Startrails over the Anglo-Australian Telescope on 23 Sep 2011. The colours of the stars are clearly seen in this image, which stacks 1h 6min of observing time. Credit: Á.R.L-S.

Finally, I chose an energetic soundtrack which moves with both 2dF and the sky. It is the theme Blue Raider of the group Epic Soul Factory, by the composer Cesc Villà. Actually, all sequences were created to fit the changes in the music, something that also gave me some headaches. But I think the result was worth all the effort.

First “AAO Guerrilla Astronomy” event: partial solar eclipse on 29 April 2014 over Sydney Harbour

Last Tuesday 29th April the Earth, the Moon, and the Sun aligned to produce one of the most spectacular astronomical phenomena we can see: a solar eclipse. The 29th April solar eclipse was actually not a total eclipse (i.e., the disc of the Moon didn’t cover all the disc of the Sun) but an Annular eclipse. The annular phase could be only visible in Antarctica, but a partial solar eclipse was seen throughout Australia in the late afternoon. More information about this solar eclipse can be found in the NASA Eclipse Website managed by the astrophysicist Fred Espenak.

The Sun would be eclipsed by the Moon during the sunset, it was then a perfect opportunity to get some nice photos of the eclipsed Sun with some famous buildings such the Sydney Opera House or Sydney Harbour Bridge. With this excuse, but also with the idea of showing the wonders of Nature to the public, a group of astrophysicists working at Australian Astronomical Observatory (AAO) decided use this solar eclipse to organize our first “Guerrilla Astronomy” event (*). The aim of these activities is to set up amateur telescopes in a public area (a park or a shopping center) and explain to the public who is around what Astronomy is, what astronomers do, and what the “Australian Astronomical Observatory” is. More of these events are coming in the future, but this was our first “test” to see how we can organize and manage the activity.


Participants to the first AAO “Guerrilla Astronomy” Event. From right to left, Stuart Ryder (AAO/AusGO), Kyler Kuehn (AAO), Paola Oliva-Altamiro (Swinburne/AAO) and Ángel R. López-Sánchez (AAO/MQ). The laptop shows the only good image we could get of the eclipse using my telescope. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain, 29 Apr 2014.
Photo Credit: Stuart Ryder (AAO/AusGO).

Given the time and position of the Sun during the eclipse, we decided that a really nice spot to prepare our telescopes would be Mrs Macquarie Chair point, in the Domain, Sydney Botanic Gardens. From there a very dramatic view of the Sydney Opera House and the Sydney Harbour Bridge is seen. We first requested permission to do this to the authorities of the Domain, who were really nice and even allowed us to park by free. Actually, they also came along to see the eclipse and they liked our idea of organizing more “Guerrilla Astronomy” events there in the nearby future.


All set up for eclipse: two telescopes (Stuart’s at the right, mine at the left), the AAO banner, my laptop and camera to take photos through the telescope, the eclipse glasses and extra information about the eclipse to give to the visitors. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain, 29 Apr 2014.
Photo Credit: Ángel R. López-Sánchez (AAO/MQ).

It was four of us, Stuart Ryder (AAO/AusGO), Kyler Kuehn (AAO), Paola Oliva-Altamiro (Swinburne/AAO) and myself, who participated in this first “Guerrilla Astronomy” event. Just to have everything ready on time, we were setting up telescopes, AAO banner and laptop around an hour before the beginning of the eclipse. The weather seemed very clear in the morning, but in the afternoon, as we feared, some clouds started to arrive from the west. We already knew this would be a killer… but we had to try!


Kyler and visitor using the solar glasses. First AAO “Guerrilla Astronomy” Event: partial solar eclipse on 29 April 2014 over Sydney Harbour. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain.
Photo Credit: Paola Oliva-Altamiro (Swinburne/AAO).


Little girl using the eclipse glasses. First AAO “Guerrilla Astronomy” Event: partial solar eclipse on 29 April 2014 over Sydney Harbour. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain.
Photo Credit: Paola Oliva-Altamiro (Swinburne/AAO).


Visitors, but clouds please go away! First AAO “Guerrilla Astronomy” Event: partial solar eclipse on 29 April 2014 over Sydney Harbour. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain.
Photo Credit: Paola Oliva-Altamiro (Swinburne/AAO).

We actually were a bit lucky at the beginning, and hence we could see the Sun within thin clouds and follow the eclipse for 10 minutes. I even could take a nice image:


Partial Solar Eclipse from Sydney on 29 Apr 2014. Telescope Skywatcher Black Diamond D = 80 mm, f = 600 mm + CANON EOS 600D at primary focus + Solar filter. Just 1 frame at ISO 400, 1/8 s, colour processing using Photoshop. 29 April 2014 @ 16:20 AEST ( 06:20 UT ). First AAO “Guerrilla Astronomy” Event: partial solar eclipse on 29 April 2014 over Sydney Harbour. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain.
Photo Credit: Ángel R. López-Sánchez (AAO/MQ).

After that, thick clouds arrived and this happened:

5-seconds timelapse video obtained combining 25 images taken with Telescope Skywatcher Black Diamond D = 80 mm, f = 600 mm + CANON EOS 600D at primary focus + Solar filter, at ISO 400, 1/8 s, showing how the clouds completly cover the eclipsed sun. 29 April 2014 @ 16:20 AEST ( 06:20 UT ). The direct link to the YouTube video is here.
Credit: Ángel R. López-Sánchez (AAO/MQ).

Once the Sun was completely covered by thick clouds we just waited and hoped for a little gap, but unfortunately this never happened and we didn’t see the Sun again that day.


Stuart and his telescope, Kyler and visitors, all hoping the clouds go away. First AAO “Guerrilla Astronomy” Event: partial solar eclipse on 29 April 2014 over Sydney Harbour. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain.
Photo Credit: Paola Oliva-Altamiro (Swinburne/AAO).


The eclipsed sun is setting behind those think clouds. First AAO “Guerrilla Astronomy” Event: partial solar eclipse on 29 April 2014 over Sydney Harbour. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain.
Photo Credit: Ángel R. López-Sánchez (AAO/MQ).

Well, it would have been really nice to see the eclipsed sun setting over the Sydney Harbour Bridge and sinking later close to the Sydney Opera House, I’m sure the images and time-lapse video would have been quite spectacular, but the best I got was this image:


An eclipsed sun should be setting around there… Imagen taken using a Telescope Skywatcher Black Diamond D = 80 mm, f = 600 mm + CANON EOS 600D at primary focus. First AAO “Guerrilla Astronomy” Event: partial solar eclipse on 29 April 2014 over Sydney Harbour. Mrs Macquarie Chair, Sydney Botanic Gardens / Domain.
Photo Credit: Ángel R. López-Sánchez (AAO/MQ).

In any case, all four AAO participants were very happy about how the event was and, as I said, we are expecting to repeat these “Guerrilla Astronomy” activities in the nearby future.

Next solar eclipse to touch Australia will be on 9 March 2016, but it will also be a partial eclipse only visible on the northern and western parts of the continent. The next total eclipse to be seen from Australia will happen on 20 April 2023 and it will just touch the coast of Western Australia. We have to wait until 22 July 2028 to see a total solar eclipse in Sydney. Actually, Sydney is almost exactly in the center of the totality.

More photos of this event can be found in this Flickr Album.

(*) Note that the word “Guerrilla” comes from Spanish, however the name didn’t come from me but from an idea my colleague Amanda Bauer (AAO Outreach Officer) had some months ago. As a native Spanish speaker I have to confess it is really hard to hear the pronunciation of “Guerrilla” following English phonemes as “Guerrilla Astronomy” sounds almost identical toGorilla Astronomy“. I would encourage to try to pronounce “Guerrilla” as it is said in Spanish (geˈri.ʝa) to be released of this confusion, but of course that is only my modest suggestion than can be completely ignored…