The Transit of Venus on HAM Radio

Bob Bruninga, WB4APR

Transit of Venus 2004: On June 8th, 2004 at 11:25:29 UTC the Transit of Venus (4th contact) was observed by Astronomers and Engineers at the US Naval Academy on Farragut field at the location N38 58.64 / W76 28.84. Equipment used was a 10 inch meade reflector and camera obscura made from a 6 foot cube communication shelter with pin hole in door. Perfect skies. Photo at left shows Astronomy Professors Albert and Katz and former midshipman Hale (82) of comet Hale-Bopp fame. By the time of Sunrise on the East coast of the US, the transit was mostly complete with only the 3rd and 4th contact remaining as Venus exited the disk of the Sun. We had monitored Ham Radio for contact with other observers but no one else was heard on AMSAT net 14.282 MHz. Time was 7:25 AM EDT.

This Transit Of Venus across the face of the Sun was the first occurrence in more than a century. Unlike eclipses, this event has only been witnessed by humankind 6 times in the past, and this was the first ever since the invention of Radio to allow instant comparison of observations from around the world at the speed of light. We had hoped to use Ham radio to link observations from other interested Ham Radio operators around the world for instant display on APRS and for sharing this experience.

CAMERA OBSCURA:In addition to the modern Meade Telescope we wanted to reproduce the technique used by 17th century observers to observe the sun. This consisted of a pin-hole in the side of a darkened room. In this case, we used a communications shelter with a small pin-hole in the door as shown below. You can clearly see Venus to the lower left of the Sun's disk:

The Transit of Venus is a fascinating event historically as it gave early astronomers the first mechanism with which to actually measure the distance from the Earth to the Sun and confirm their underestanding of the size of Venus. During the 6 hour or so event, there are 4 critical times as shown below. These instances will occur at slightly different times for observers at different Earth locations because of parallax. But generally begin at 0513z and end at 1126z.

The parallax due to the separation of different observers will give enough differences in the observations to make meaningful measurements of the geometry of the event.

Naval Academy Team: Since this once-in-a-lifetime event will mostly only be visible in the Eastern Hemisphere except for a few minutes after sunrise on the USA East coast, the plan had been to take a team from the US Naval Academy lead by Professor Jim Huddle on an Innovations In Travel cruise ship going up the Nile. Another team lead by Professor Elise Albert was headed to the Mediteranian with your's truely. But the ship contractor went out of business.

Some History: Many people don't realize that the mission of Captain Cook's 'round the world voyage in 1769 was to observe the transit of Venus in Tahiti.. (and secretly to lay clam to Antarctica if it existed)... Anyway, since it took him 3 years to complete his voyage, it took a while to collect these observations from other corners of the globe and then without computers or accurate global time, or any means of distance communications it took years for the data to be assemilated and analyzed.

Radio and Wireless: Fortunately, for this 7th Transit of Venus, we can take advantage of another momentous discovery in Physics heralded by Marconi at the turn of the last century. His demonstration of the long distance communications capabilities of Radio waves in 1902 will add a new dimension to the Transit event by offering, for the first time in human history, the ability to witness the event simultaneously from excursions to the four corners of the world via the miracle of electronics communications. The map below shows the areas of the Earth where the Transit will be visible from the beginning (between the red lines) to the end (between the yellow lines). Observers between India to Germany have the potential to see the complete event.

Communications: My participation in this event is to lead the Amateur Radio community into using the invention of radio to herald this event from all corners of the globe. We will use links via ionospheric propagation (HF) and satellite to share the event between the numerous excursions that will be taking place on that day throughout the world. Here are some of the ideas in work to develop support for this event:

  • HF Net: We will maintain communications via ionospheric propagation for check-in's from participating sites.
  • Amateur Satellite AO-40: will be ideally situated (But is Currently INOPERATIVE)
  • Digipeating via ISS: Participating observers will digipeat their observations
  • ISS Certificates: Some club could take charge of this special event and issue certificates
  • Expedition Tracking: Travels of expeditions will be tracked by GPS and relayed live to the APRS web page.
  • APRS Objects: Uplinked APRS objects will follow the ground track of the 4 contacts across the surface of the Earth.
  • Transit Tracking: And lastly we will use the coordinate tracking capabilities of the global APRS network to collect instantaneouse Venus position reports from other stations around the globe as shown below.

    If you are a HAM radio operator that will be involved in any scientific or public observations of this event, let us know so we can be watching the global APRS map for your team and your data if you will be posting APRS objects...

    Images of the Event: Although most images you will see of the anticiapted event will show straight line tracks and parallel paths for different observers at different longitudes, this is only after the images have been aligned with the plane of the Earths orbit. If observers orient their observations relative to local horizontal, instead of polar, then their image will not be aligned with others because of the different angle imposed by their 3D difference in longitude. And such tracks will not be straight lines either, because the Earth is rotating about 90 degrees during the 6 hour event. What we hope to plot in real time via APRS object reports are the actual (local horizontal) reports from different observers. THe results may appear as below...

    In order to get everyone to a consistent size, we need to work on a projection system that can project the Sun's image onto graph paper that is either 2.5" or 25 cm radius. The reason for the 2.5" or 25 cm projection size is because the size of APRS area circle objects are granular in size. This size yields a reasonable closefit to graph paper to yield a 500x500 grid. The following object in APRSdos plots a 2.5 minute radius yellow circle.


    To see how to do this in APRSdos, click here.

    Your challenge is to get the Sun's projection onto the graph paper to exactly that size, or conversly, to make your own GRID scaled to your own size projection so that it is evenly divided into +/- 2.50 minutes of LAT/LONG with enough grid lines so you can estimate position to the nearest 500'th the diameter of the Sun...

    There is a simple commercial product for projecting the sun. Its simply a hole in a box in which you put a small lens/telescope/(or half a binocular) and then bounce that off a mirror back into the box where the image is hidden from the bright sun. I like it's simplicity. See it

    This map is a LIVE FINDU.COM map of any reported sightings. Between now and 8 June you can practice your uplink and see if it shows up here: Now that this is on line, it was a poor choice becasue 00N/00W is a noman's land where null APRS posits some times go. Hence, you will see some unintended ICONS at the center 00/00:

    PASSES OF THE ISS DURING THE TRANSIT: The plot below shows all of the passes of ISS over HAM populated areas during the 6 hour event. It is recommended that a NET-CONTROL station take checkins on each bird (AO-27, and SO-50) and Packet be used on ISS to report from various opservation sites:

    USE OF AO-40 CANCELED: We had planned to use AO-40 for constant communications throughout the event but it died early this year. But this portion of the web page is retained for historical purposes...

    Satellite Communications: Throughout the Transit, the largest and most capable satellite in the Amateur Satellite Service, AO-40 will be in view of most of Asia. This satellite would have allowed excursions observing the event to communicate directly to one another if they are in the footprints shown below. AO-40 is in a highly eliptical orbit but is fortunately in the right place at the right time but unfortunately, inoperative..

    Before it's demise, Amateur Radio Operators could work the AO-40 satellite using a typical portable satellite station as shown below. The advantage of AO-40 is its long 8+ hour dwell time over the area of the Transit. During the same 6 hours there will be several other Low Earth Orbiting Amateur Satellites to provide short duration special event communications. The exact times of these passes will be posted as the event approaches.

    THIS HAM RADIO PAGE IS only a draft and should not be relied on for detailed astronomical data. For more Astronomical details on the Transit, see

  • European Southern Observatory.
  • See times and world views)
  • see the Orpington Web page
  • Venus Project .
  • NASA's page.

    Bob Bruninga, WB4APR
    Senior Research Engineer
    US Naval Academy Satellite Earth Station

    This page was first posted on 27 August 2003, the closest approach of Earth to Mars in 20,000 years.

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    The Naval Academy is a registered user of APRS. The purpose of this web page is to show several applications currently in use at this site and should not be considered as an advertisement or an endorsement of any commercial product.