UCL Observatory (UCLO)


Transit of Venus, 2004 June 8

On the morning of 8th June 2004, an extremely rare astronomical event, a Transit of Venus, took place for the first time since 1882. No one alive today saw the previous transit.

Images of the transit were obtained with the telescopes at UCLO. The images shown on these pages were obtained with the Fry 8-inch Cooke refractor, operating with an H-alpha tunable filter and an Astrovid 2000 video camera; and a Meade LX200 10-inch telescope with white-light filter and an Astrovid Planetcam colour video camera.


H-alpha images of the transit obtained with the Fry 8-inch Cooke refractor

H-alpha images of the transit obtained with the Fry 8-inch Cooke refractor. Each image is the sum of 50 individual video frames in a 2-second video segment. The chromosphere can be seen at the limb of the photosphere, and is occulted by Venus after 3rd contact.

Summary of the event

Some early images of the transit (screenshots) and pictures of visitors enjoying the event at UCLO are available here.

Dr. Mike Dworetsky, Director of the Observatory, writes:

``The University of London Observatory undertook a large public open event for this literally once-in-a-lifetime occasion.

The Transit began at 06:19:55 BST and ended at 12:23:38. We were fortunate to have excellent weather conditions throughout the 6+ hours and observed from before first contact until after fourth contact ... Successful observations were obtained with the Fry telescope in H-alpha (0.6A FWHM), with the Meade in white light, and with visual instruments mounted on the roof terrace of the Wilson building. The only problems were due to thin cirrus which reduced contrast from time to time but never stopped the observing.

We counted a total of 560 visitors, including many students and some staff from UCL, as well as many local residents who were alerted by an article we helped to write for the local paper.

The silhouette of Venus was clearly visible against the chromosphere for about two minutes before and after the Transit. The famous "black drop" phenomenon was clearly seen in white light observations with the Meade, but remarkably there was no obvious problem with determining times of contact for H-alpha observations. The chromospheric observation was very helpful in determining the instant of first contact, something that was very difficult for 18th and 19th century observers.

Accurate timing of the precise moments of the contacts (when Venus is just touching the apparent edge or limb of the Sun on the outside or inside of the disk) was critical for the determination of the distance to the Sun, which was the goal of all their efforts.

I determined the following contact times, with differences from exact predictions, live during the video for three of the contacts and from a preliminary scan of the mpeg version a day later for a fourth contact:

These could be improved upon once we can work from the digital frames.


  C1 05:19:45 UT(10 sec early)
  C2 05:39:26(13 sec early)
  C3 11:03:58( 8 sec early)
  C4 11:23:26( 2 sec early)

The video of C2 was poor due to seeing problems but we may be able to improve the clarity by coadding the sharpest frames.

Apparently I tended to anticipate the critical moments, but got better at it with experience!''

More information

The following links provide more details of the transit itself, and other transit links:

Safe solar observing

Please note!. IT IS ALWAYS DANGEROUS TO LOOK DIRECTLY AT THE SUN without proper eye protection.

Follow these links for information on safe solar observing: