Venus

Observing the 2012 transit of Venus

The 2012 transit of Venus imaged at h-alpha wavelengths. Credit: Will Gater

A week ago I travelled to the Greek island of Kos to observe the 2012 transit of Venus – a rare celestial event where the planet Venus drifts in front of the Sun’s disc, as seen from Earth.

The hotel where I stayed was located on the north-eastern end of Kos, close to the village of Psalidi. I had chosen this site for two main reasons. The first was its shoreline location and clear view to the northeast out over the Aegean Sea.

Only the distant mountains of Turkey interrupted the horizon, but as they reached less than a degree above the horizon I knew they wouldn’t obscure much of the transit. Besides, when the Sun is that low down the distorting effects of the atmosphere are so great that getting a sharp view of the transit (when the Sun is barely a degree above the horizon) would be almost impossible.

Although the transit would be well underway by the time the Sun rose from Kos, the island’s position on the Earth meant that around 2 hours of the transit would still be left to observe. And the Sun would reach an altitude of about 20 degrees, from Kos, before Venus moved off the solar disc.

A view of the north-eastern horizon from my observing site near Psalidi.

The second reason I chose Kos as my transit observing location was that the eastern end of the Mediterranean had the best weather prospects in Europe for the time of the transit. I later found out that I wasn’t the only one with the eastern Med in mind as an observing site, as several other astronomers — including well-known German astronomer Daniel Fischer — travelled to Rhodes.

Moonrise over Kos two nights before the transit. Credit Will Gater

Imaging the transit with a static photo tripod, PST & DMK 21AU618.AS CCD camera

I was able to take two telescopes with me to Kos. The first was the de-mounted optical tube assembly from an ETX90EC with a Baader AstroSolar Safety Film solar filter. I have used this telescope on observing trips several times, including the 2006 total solar eclipse in Turkey, as its compact size is perfect for travelling. However this time because of hand luggage weight constraints I had to carefully pack it up and send it to Greece in my hold luggage.

Unfortunately a quick star test on the night of my arrival in Kos showed that it had slipped slightly (but noticeably) out of collimation — so my transit images from the ETX OTA are not as sharp as they could be. The second scope I took with me was a Coronado PST. I carried this as hand luggage along with a DMK 21AU618.AS CCD camera and the Baader solar filter.

A test image captured with a static photo tripod a few days before the transit.

Both telescopes were used, one at a time, with a heavy photographic tripod. Imaging the Sun with my Canon 550D DSLR and the ETX scope was a fairly easy affair — only single, short, exposures were needed. However the PST/DMK/static photo tripod setup presented a few imaging challenges. Namely, how to capture an AVI video through the DMK/PST without blurring the image or letting the Sun drift out of frame while the video was being captured.

There was no way I would be able to take a tracking mount with me to Greece; so in the months leading up to the transit I practiced hand guiding the alt-azimuth controls of the photographic tripod so that the Sun stayed in frame, in roughly the same location. It was difficult to say the least, but it did work and Registax was able to process the videos without any ‘ghost’ images. Above is a test — hand tracked — PST image captured two days before the transit.

Dawn breaks over Kos on the morning of the transit.

The morning of the transit was clear, with only a few thin haze clouds hugging the horizon. Yet as the dawn began to break a few clouds started to bubble up over the coast of Turkey. One cloud in particular (seen in the image below) had me worried, as it was threatening to move right in front of where the rising Sun was about to appear. Thankfully though these clouds moved away — and some of the haze appeared to dissipate — a few minutes before the first rays of sunlight appeared over the mountains.

The north-eastern horizon moments before sunrise.

My first view of the transit was, as expected, heavily distorted by various atmospheric undulations. It was actually quite surreal to see the silhouette of Venus, through the eyepiece, being smeared up and down — as if someone was stretching and compressing the whole solar disc. The series of images on the left (click the thumbnail to get a bigger version) shows this effect clearly; they were taken just as the Sun was appearing over the distant Turkish mountains.

As the Sun climbed higher in the sky the atmospheric distortion lessened and I was able to begin imaging the transit in earnest. Below are a few of the shots I was able to capture.

The 2012 transit of Venus imaged at h-alpha wavelengths. Credit: Will Gater

A full disc view taken with a 550D, ETX90EC & Baader solar filter. Credit: Will Gater

The 2012 transit of Venus imaged at h-alpha wavelengths. Credit: Will Gater

The 2012 transit of Venus imaged at h-alpha wavelengths. Credit: Will Gater

The development of the famous ‘black drop’ effect. Credit: Will Gater

Almost over! Venus edges off the solar disc. Credit: Will Gater

Towards the end of the transit a large cumulus cloud bank formed to the southeast and began to slowly drift in the direction of the Sun. As Venus was moments away from slipping off the solar disc, the wispy edges of the cloud began to encroach onto the Sun until finally the transit was completely obscured. And so began the 105 year wait for the next time that Venus glides gracefully across the face of our star.

One final note: throughout the transit I was using specialist solar filters to observe and photograph the Sun. Never point an unfiltered telescope, unfiltered pair of binoculars etc. at the Sun. You will damage your eyes and almost certainly blind yourself. If you want to observe the Sun only use specialist certified solar filters that have been fitted correctly (and thoroughly checked) and that have been purchased from a reputable astronomical supplier. Be sure to follow any usage instructions carefully. Finderscopes etc. should also be filtered or removed.

All images © Will Gater 2012

Watching a wandering star

Over the past few weeks it’s been hard to miss Venus shining away high in the west after sunset. At the end of March it was less than 3 degrees from the crescent Moon, while the first week of April saw Venus drifting past the Pleiades star cluster. Below I’ve collected together some pictures of the planet that I’ve taken recently; clicking on each one will take you to a larger version.

The wide-field pictures were all taken with a Canon 550D DSLR and a zoom lens, while the close-up (showing Venus’s phase) was captured with a Philips SPC900NC webcam and an 8-inch Schmidt-Cassegrain telescope.

Two glittering planets meet the Earthshine lit Moon

Venus, Jupiter & the crescent Moon. (Click for full-size version) Credit: Will Gater

Jupiter, Venus and the crescent Moon are putting on a wonderful show in the west after sunset at the moment. The picture above shows the view last night with Jupiter and the Moon separated by roughly 3 degrees. A close-up of the view (below) shows the Moon and Jupiter as well as two of the Galilean satellites – Ganymede and Callisto. Tonight the view is no less spectacular with the brilliant Venus and the crescent Moon a little over 2 degrees apart. Pop out and see them if you can.

While you’re out, look out for the effect known as ‘Earthshine’. This is where sunlight reflected off the Earth’s bright cloud tops lights up the part of the Moon that isn’t directly lit by the Sun; it’s best seen when the Moon is a thin crescent, like it is at the moment. You can see Earthshine clearly illuminating the face of the Moon in the image below.

Jupiter, the crescent Moon & Earthshine. (Click for full-size version) Credit: Will Gater