Transit of Venus (2004)
After a 122-year wait, Venus crossed the face of the Sun — a black dot drifting for six hours.
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The moment of Transit of Venus (2004): https://nowsky.org/e/venus-transit-2004 — opens at the right place and time, replayable, no login.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
On 8 June 2004 Venus crossed the face of the Sun for the first time in 122 years. From 05:13 to 11:26 UT — six hours — a black disk moved across the Sun, visible from start to finish in Europe, Africa and Asia; Korea saw it from about 2 pm until sunset.
The previous transit had been on 6 December 1882, so no living person had witnessed one. Schools everywhere held solar-projection events, and a generation of children came away with the memory of a black dot on the Sun.
Transits of Venus carry unusual history. In 1761 and 1769 astronomers timed the transit from points around the globe and used the parallax to compute the distance to the Sun for the first time; Captain Cook's voyage to Tahiti in 1769 was mounted for that purpose. Observers in 2004 repeated the method as a classroom exercise.
Transits come in pairs eight years apart, then rest for more than a century. The partner of 2004 was 2012, and the next is 2117. Move the orbit view to 8 June 2004 to reproduce the Sun–Venus–Earth alignment.
Why it matters
The 2004 transit revived the measurement of the astronomical unit as a public exercise. In the VT-2004 project led by the European Southern Observatory, 2,700 teams timed the contacts from their own locations and computed 1 AU from parallax — within 0.007 percent of 149.6 million km.
It was also a rehearsal for exoplanet science. Precise measurements of the 0.1 percent dip in the Sun's brightness during the transit became the reference for interpreting the signals of the Kepler space telescope (launched 2009), which finds exoplanets by the same principle.
Comparing the photographic plates of 1882 with the digital imagery of 2004 showed how far observing technology had come in 122 years, and laid the groundwork for the large campaigns with Hubble and SDO at the 2012 transit.
How to watch
Move the orbit view to 8 June 2004, follow Earth and set the Sun as the gaze target, and Venus sits exactly between them. Slow the playback to see how the six-hour transit plays out along the orbits.
Select Venus in the sky view for whether it is in the dawn or dusk sky from your location, with its phase. During a transit Venus shares the Sun's position, so moving the time to 8 June 2004 draws Venus over the solar disk.
The next transit of Venus is 11 December 2117; before that comes a transit of Mercury on 13 November 2032. Mercury's silhouette is far smaller than Venus's and needs a filtered telescope.
See this for yourself — replay the moment in the orbit view
Background
From Jeremiah Horrocks's first observation in 1639 until 2004 there had been only six transits (1639, 1761, 1769, 1874, 1882, 2004). International expeditions went to Japan, India and Egypt for the 1874 transit, when photographic plates were first used.
The "black drop" effect at Venus's limb had bedevilled contact timings since 1761. Observations in 2004 confirmed it as a combination of atmospheric seeing and the darkening of the Sun's edge.
The partner transit of 6 June 2012 was the last of the twenty-first century and was visible in full from Korea. The next pair falls on 11 December 2117 and 8 December 2125.
The classic goal of transit observation — measuring solar parallax — has long since been replaced by radar and spacecraft tracking. The astronomical unit was fixed to the kilometre by radar echoes from Venus in the 1960s, and in 2012 the International Astronomical Union defined it as exactly 149,597,870.7 km. So the parallax exercise of 2004 was not an attempt to obtain a new value but an educational experiment repeating, under the same sky, the method by which eighteenth-century astronomers first sized the solar system. That students’ measurements landed within 0.1 percent of the defined value shows how powerful the method was.
FAQ
How long did it take?
About six hours, from 05:13 to 11:26 UT.
Was it visible from Korea?
Yes — it began around 2 pm local time and most of the transit was visible until sunset.
Why 122 years?
Transits come in pairs eight years apart separated by gaps of 105.5 or 121.5 years; after 1882 the next was 2004.
When is the next transit of Venus?
11 December 2117; 2012 was the partner of 2004.
Related
- Transit of Venus — last this century
- Transit of Mercury (2032)
- Mariner 2 — first planetary probe
- Venus — object index
- The Sun — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.