Transit of Venus

Transit of Venus, 8 June 2004

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Introduction

On the 8th June, a Transit of Venus occurred. The entire event was visible from the UK (including London) during the morning. It was also visible from the following places:

Part of the Transit was visible around Sunrise from most of North America, southern Central America, the Caribbean, western and southern Africa, and northern South America. Part of the Transit was visible around Sunset in Indonesia, Australia, Western China, Vietnam, Malaysia, and southern Alaska.

The map below (© Fred Espenak) indicates three regions: the entire Transit was visible (yellow); part of the Transit was visible (light blue); the Transit was not visible (dark blue).

Transit Map

Transits occur when an Inferior Planet (one that orbits closer to the Sun than the Earth) passes directly in front of the Sun. It will then appear as a black dot moving slowly across the face of the Sun. Only two planets can transit across the Sun as seen from Earth: Mercury and Venus. Transits of Mercury occur about 13 times per century and are not visible with the naked eye.

Transits of Venus are very rare: the previous one occurred in 1882. Only five had ever been observed. They are visible with the naked eye. Transits of Venus can only occur in June and December. They occur in pairs separated by 8 years. Each pair occurs after 105 or 121 years. This is a list of recent and future transit dates:

From London, the 2004 Transit lasted for just under 6 hours and 04 minutes. In the northern hemisphere, the planet was seen moving left to right across the lower part of the Sun. The following diagrams define the terms used for the Transit:

Exterior Ingress
Exterior Ingress
Interior Ingress
Interior Ingress
Mid-Transit
Mid-Transit
Interior Egress
Interior Egress
Exterior Egress
Exterior Egress

History

There is some evidence of a Transit of Venus being observed in Kazakhstan in the year 910.

Johannes Kepler predicted transits of both Mercury and Venus in November and December 1631 respectively. On 7 November, Pierre Gassendi saw the Mercury transit. This is the first recorded case of a transit being observed. The Transit of Venus a month later was not visible in Eurasia and was not recorded.

Jeremiah Horrocks and William Crabtree, two amateurs, became the first to observe and record a Transit of Venus when they saw the event of 1639. Kepler had failed to predict this Transit, but Horrocks, a vicar by profession, calculated that it would occur on 4 December. He observed all day between giving his sermons (it was a Sunday) and finally saw the black spot of Venus in the afternoon up until sunset.

In 1716, Edmund Halley (of comet fame) published a paper that described the use of a Transit of Venus to determine the distance to the planet and thence to the Sun. At that stage the scale of the Solar System was known - if any single distance could be determined then all distances could be calculated. The method involved making accurate timings of each phase of the Transit from different locations around the world.

In the 1760s, the English navigator, James Cook, lead an expedition into the southern hemisphere to observe the Transit of 1761. This was unsuccessful but lead to important scientific and geographical discoveries while he was waiting for the transit of 1769. Guillaume Jean Baptiste Le Gentil went to the French colony, Pondicherry in India only to find that the British had captured it. When he returned eight years later, it was cloudy. Charles Mason and Jeremiah Dixon (of Mason-Dixon Line fame) observed from South Africa. Maximillian Hall ended up in Siberia and was nearly attacked by locals.

Unfortunately, the presence of an atmosphere on Venus, meant that the exact times of internal ingress and egress could not be determined. What happens is that a "black drop" accompanies the planet as it passes internal ingress. This "drop" makes it difficult to determine the exact time of the ingress. By the time the "drop" clears, the planet is well onto the Sun's apparent surface and the exact time of internal ingress has passed.

The Black Drop
The Black Drop

Details

The table below lists the times for London.

Event UK Time (BST) Sun's Altitude
Exterior Ingress 06:20:55 12°
Interior Ingress 06:40:39 15°
Mid Transit 09:23:39 40°
Interior Egress 12:04:06 59°
Exterior Egress 12:23:28 61°


8 June 2004

1am on Tuesday 8 June and we were still not asleep.

The bag was packed with cameras, lenses, film, mylar (filter), a small telescope, spare batteries, white card, sellotape (that's sticky tape for USA readers), and eclipse glasses (some dating from the 1991 eclipse in Mexico). Another box lay in the kitchen with snacks, fruit, biscuits, soft drinks, water as well as tea and coffee making equipment.

The sky was clear, the weather prospects were good, anticipation was high.The final post-shower preparations and body maintenance were being performed. Several alarms were set including a telephone wake up call. This was the first transit of Venus since 1882 and we didn't want to miss it.

I slept fitfully with the excitement. Memories of being clouded out for the solar eclipse of 1999 invaded by dreams turning them into nightmares. Finally a voice in one of my dreams said "wake up - it's 5 o'clock" and I was back in the real world. It was daylight - ahh the long days of June (sorry all you in the Southern Hemisphere!). It was clear and sunny - a golden light illuminating the higher portions of nearby houses.

Wash, dress, cereals (crunch, crunch). Clocks set to GMT. Mobile phones charged. Don't forget house and car keys. I was ready.

It was a clear and quick drive for the 25 minute ride to Alexandra Palace, a huge building set in a park on top of a hill with a fine southerly view over London. Perfect, apart from the car park area being closed. We dumped the car on a double yellow line hoping it was too early for a ticket and carried our stuff to the benches outside the bar. They were still covered with beer glasses and other detritus from the previous night. I cleared an area and began setting up.

Firstly I attached my little telescope to its rickety tripod and projected a fine clear image of the Sun onto a piece of white card. More card covered the telescope and blocked out the extra light. This was the traditional technology. Next I taped silver mylar filter onto the end of my 200mm lens on my Olympus OM2N camera. The clock was ticking to the time of first contact 6:20.

The car park opened and Talaat brought the car up closer. Now we could have some coffee.

Mike and Theresa (Southby) arrived.

They were taller and bigger than us (I love you both really) - their car was bigger than ours (it looked like a tank and it had a canoe on the roof) - their equipment was bigger than ours.

Out came chairs and foot stools. Out came a huge ice box full of enough food for a three week camping trip. Out came a massive Meade telescope with huge tripod that looked like it could withstand an earthquake. Out came a car battery to drive a laptop computer that would control the telescope and take images automatically. More worryingly, out came a handbook and a puzzled look on Mike's face.

In the end, the laptop found a better use in holding up my white card for my projected image. The telescope (with a solar filter) produced a breath-taking image of the Sun complete with a pair of small sunspots. After a little effort with compass and spirit level Mike managed to track the Sun automatically with only slight adjustments needed.

A wonderful tripod (thanks Theresa) allowed my camera to take longer exposures in the dim mylar filtered light.

First contact; and there it was. A small dent in the Sun as Venus began its passage across the Sun. We could see it on the projected image as a complete whole; we could see it through eclipse glasses with the naked eye; and we could see it in detail through the Meade telescope with the sunspots. Projection, naked eye, telescope. A perfect combination. Mike used his digital camera through the Meade eyepiece to obtain some stunning pictures.

Second contact (6:40). Venus was now completely on the Suns disk.

Time for hot cross buns (a type of cake for our USA readers), cherries, cold drinks and chocolate coated toffees which had melted in the Sun. I rang Bob (Snell), observing through his 30cm (1 foot) thick telescope from the north of England. He had some misty cloud but also clear periods. He was using up lots of film. John (Mears) arrived with friend Audrey.

The next six hours passed pleasantly and quickly. Photos were taken, drinks were drunk, phone calls were made and received and t-shirts were placed on heads as it got hotter. Passers-by were aroused by the spectacle.

One woman came to look and told us that the transit was "producing healing energy". Another wanted to know about "the emotional aspects of the transit". Two Polish women came and gleefully looked at everything we showed them. A Gujerati woman (and child) came. The numbers increased as the morning wore on. Various groups of shirtless youths, elderly couples, joggers and cyclists stopped to ask, look and reflect.

We increased our photo taking around 9:23, the time of maximum transit.

Towards the end my projection became unstable - it had got ("gotten" for our USA readers) windy and the Sun was so high in the sky that my telescope kept blowing over from being off-balance. We still managed to follow the transit to third and fourth contact (12:04 and 12:23), especially through the powerful Meade.

Finally it was over. At that moment a man who had been sitting and drinking on a nearby table came over for a look.

I looked around. Our skins was red; our mouths were dry. We packed and sought refuge in the bar where refreshing liquid was consumed. A sleepiness overcame me. We said our goodbyes, drove home an collapsed in bed. A couple of callers had to be cursed "we are ringing on behalf of..."

It had been a success - for once the British weather played its part.


The Images

The links below contain photographs by my friend, Mike Southby, of the 2004 Transit of Venus.

General images of the Transit including a full image, a close up of Venus and a pair of sunspots.

A selection of images showing the Sun's disk with the planet Venus moving across.

A sequence of images showing the planet Venus leaving the Sun's disk, including the black drop.

Images of the people at Alexandra palace on the day of the Transit.