European Science & Technology Week 2004Visit the websites of the VT-2004 organisers
European Southern Observatory (ESO)European Association for Astronomy Education (EAAE) Observatoire de ParisInstitut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE)Astronomical Institute of the Academy of Sciences of the Czech Republic

Observing The Venus Transit 2004

....Guidelines for Observers!


Date : 8 June 2004

Time : approximately from 5:19 to 11:23 UT (Universal Time) in central Europe (see the Predicted Timings Table for more precise times)

WARNING : Don't look at the Sun without special filters !!!

These guidelines have been written in such a way that they will be useful for observers who do not have too much experience with astronomical observations. In particular, they are suitable for participants in the VT-2004 Observing Campaign, especially students and their teachers


  • Find the relation between Universal Time and your national legal time and compute the time interval for the Venus transit at your place using UT given above or in the Table with the predicted timings. If in doubt: Ask your VT-2004 National Node for help or consult the VT-2004 web-pages.
  • GO through the following steps:
    1. Visual observations (no instruments): GO TO 2
      Projection method GO TO 3
      Using binoculars or telescopes GO TO 4
    2. The event is observable by eye (Venus has about 1 arcmin diameter, comparable to big sunspots); one needs special dark glasses (the ones used for the solar eclipse). See Special Filters section.
      GO TO 5
    3. The projection method is relatively safe. For the projection you can use:
    • Simple ' Camera Obscura ': take a larger paper-box, make there a small hole and direct it towards the Sun - you will see the solar disk projected on the internal wall of the box. Adjust the size of the hole accordingly to get the best possible contrast.
    • Special kits called ' Venuscope ' or ' Solarscope ' can be ordered for about 80 Euros at e.g. or
    • Small telescope or binocular , behind the eyepiece you attach the white screen and you will see the Sun projected on it (the distance has to be properly adjusted). Improve the projection by installing your screen in the umbra of another screen patched around the eyepiece. For binoculars, use only one half and cover the objective of the other one, otherwise you get two overlapping images. For telescopes, be sure to cover the entrance lens of the finderscope, otherwise someone might get hurt by the beam from this little scope! This method does not require any filters, BUT take care that the observers (students) will not look DIRECTLY into the binocular!
      With the projection method you should be able to see the sunspots. You can take photos of the projected images during the transit.
      GO TO Advanced section
  • Looking through the telescope is less safe but more exciting for students - see Special Filters. You must adjust the special dark filter to fit the full entrance aperture of your telescope or binocular. You will see the solar surface with its sunspots.
    For more sophisticated telescopic observations contact amateur astronomers or planetaria (via your National Node).
  1. Make observational tests several weeks or days before to be sure that everything works and follow the checklist. Use sunspots to test your observing tools (instruments). To know whether sunspots are visible on the Sun, look at
  2. Computer simulations of the transit on your PC can be useful and instructive (see e.g. and
  3. Test the organization of your group of observers (students) during the preparatory observations, find the most efficient way to observe the transit.
  4. If the weather is unfavourable, observe the Venus transit via the web, e.g. at the VT-2004 Central Display.

Special Filters

Coated foil filters are easy to order from e.g. Baader Planetarium for less than 20 Euros, it is a sheet 20 x 28 cm, you can cut it (comes with instructions). But act quickly, delivery takes some time. Glasses for observing the solar eclipse are also very useful. DO NOT USE other dark filters, they may be transparent to some invisible radiation (infrared or UV) which can damage your eyes!!!


For details see also the other VT-2004 web pages dealing with observations, or consult your National Node.

You need to know your geographic coordinates with a precision of at least one arc minute. A geographic map with resolution up to 1 arcmin is enough for position definition, the use of GPS is also recommended. Alternatively you can use

Determine as precisely as you can the times of contacts:

t1 - first contact (the disk of Venus contacts the solar disk from the outside)
t2 - second contact (the disk of Venus is fully on the solar disk)
t3 - third contact (the disk of Venus starts to leave the solar disk)
t4 - fourth contact (the disk of Venus leaves the Sun)

We thus have two external and two internal contacts.

  • Precise timing (up to 1 sec) and geographic position up to 1 arcmin are needed for good measurements. UT time-scale: a radio clock, internet server (not guaranteed!), DCF-77 radio receiver (radius 1000 km from Frankfurt/Germany, possibly more), GPS if possible.
  • For this, you may profit by using the STOPER software [click to download the ZIP-file(704k)], developed by Arkadiusz Dudka, active member of the VT-2004 programme in Poland. This programme mimics a traditional stopwatch and allows making precise time measurements with a PC. A good accuracy of the measurements is then possible, thanks to synchronization of a local computer clock with a Time Server via the Internet. The time synchronization is based on Simple Network Time Protocol (SNTP) with an accuracy of at least 50 ms. All labels, texts and the help are in English. This software may be distributed as FREEWARE, provided the author and VT-2004 are credited.
  • Times to be determined: t1, t2, t3 and t4, but the easiest is t3 and possibly also t2
  • If you have not already done it: register as observers
  • Enter your time measurements (in UT !) for processing at the same web site.
  • You can take transit images with digital cameras, videos and web-cams. A "pipeline" will be available for connection between observers and the VT-2004 server, see VT-2004 webpage for instructions how to submit your digital images for processing.


  1. Decide how you will observe the transit
  2. Prepare your tools:
    • order filters, Venuscopes etc.
    • prepare binoculars or telescopes
    • attach projection screens to telescopes
    • prepare your photo cameras and videos
  3. Test your observing method well before the transit. You can use sunspots for tests if they are on the Sun - this can be seen on the web each day.
  4. Find the way how to follow the Sun on the sky - it MOVES and you have to move your instruments accordingly!
  5. Instruct the observers (students) on what to do, organize your group.
  6. Give to the observers (students) the SAFETY INSTRUCTIONS!
  7. Make sure that you know the predicted times of contacts in UT and in your local time
  8. Be present on the right time at the right place!

    Advanced observations - measurements:

  9. Test your source of time to be ready.
  10. Train the observers (students) to determining the contact times; for that you are advised to use the PC simulations.
  11. Find your precise geographic coordinates in order to be ready to send your observational data soon after your observation was made


If you have questions in connection with these guidelines, please do not hesitate to contact the organisers via email at