Following the shadow of Venus & other heavenly sights

In Northern Colorado on June 5 the shadow of Venus will begin creeping across the disk of the sun near sundown. This happened eight years ago in 2004, but won’t happen again until 2117. It didn’t happen at all in the twentieth century, but twice in the 19th. In the 18th century, this transit of Venus sparked the powerful countries of the day to launch ships and take measurements that forever changed our view of the size of the solar system. Today, the same event may help us discover Earth-like planets around other stars. Yet, as one 17-year old said while waiting to get a view of the event in Sydney in 2004, “It’s a pretty big turnout for a dot.”

[media-credit name=”Jan Herald” align=”alignleft” width=”293″][/media-credit]
Venus in transit in 2004.

A shadow dot is all an observer will see. The dot punctures one rim of the sun’s disk; then plows across the face of our mother star for nearly 7 hours before exiting at the other side. Venus is partially eclipsing the sun as it passes in front of the Earth’s orbit. If Earth and Venus orbited the sun in precisely the same plane, this event would occur five times every eight years. Because Venus’ orbit tilts 3.40 relative to Earth’s orbit, Venus only provides her shadow show in a 243-year repeating pattern that consists of two transits 8 years apart separated by 121.5-year gaps.

In the 18th century, precise measurements of transit times from widely separated spots on the globe allowed scientists to estimate planetary distances using some basic trigonometry. History buffs may recall that Captain James Cook upheld British scientific expertise and honor by taking measurements on June 3, 1769 in Tahiti. Last year, Andrea Wulf wrote Venus—the race to measure the heavens, a book that details the personal trials and triumphs of the men and women that risked lives and careers to chronicle Venus’ moving shadow.

Today, scientists using the Hubble telescope will watch light from the event bounce off the moon. 1/100,000th of that sunlight will filter through the atmosphere of Venus revealing the chemistry of its atmosphere in spectroscopic “bar codes.” Because scientists already know what that chemistry is from space probes, their measurements will test the resolution of their technique. Astronomers currently use similar methods to look for and measure the chemistries of planets orbiting other star systems. Venus, a near sister of Earth in size and mass, serves as a good proxy for Earth-like planets elsewhere in the universe.

Venus’ heft and dimensions mask serious differences with our own water world that scientists still fail to understand completely. Venus blazes in morning and evening skies near our neighborhood star, the brightest object other than sun and moon in the sky, partly because she is closer to the sun, but partly because her perpetually cloudy atmosphere reflects a lot of light. If Venus ever had oceans, they have long since evaporated. Her carbon rides in the sky as carbon dioxide rather than locked in carbonate rocks as on Earth. Venus represents a greenhouse planet set on “high pressure broil.” Surface temperatures melt lead. Surface pressures exceed Earth’s by 90 times. Volcanoes fill the atmosphere with sulfur compounds. Venus turns sluggishly, providing a day that’s longer than her year.

The Soaring Eagle Ecology Center (SEEC) will hold a viewing event for the transit of Venus at Red Feather Lakes beginning at 4 pm on June 5. Current plans call for the event to be held at either RFL elementary school or adjacent SEEC land. The Northern Colorado Astronomical Society (NCAS) will equip several telescopes with solar filters. The sun CANNOT be viewed directly without eye damage. Observers not looking through properly filtered telescopes will need solar eclipse glasses, welder’s goggles, or paper to make a pinhole projector and screen. Other stations will feature physics and weather-related activities. See more complete details at the SEEC website:

Find a complete listing of local viewing events featured by NCAS throughout the summer (sometimes in conjunction with the City of Fort Collins Master Naturalists) at Another useful website containing detailed information about the Venus transit is They also have a page detailing eye safety at
June skies will feature a full moon on the 4th with a partial lunar eclipse visible in the Americas at moonset, just before dawn. The Lyrid meteor shower peaks over the weekend of June 15 and 16 with up to 9 meteors per hour visible. On the morning of June 17 Venus joins the moon and Jupiter just before sunrise. Summer solstice occurs June 20. By then, only the memory of Venus’ shadow on the sun will remain—along with moon-reflected bar codes that may help tag other suns containing planets with rare and beautiful planets like our own—or near misses, like the glowing jewel of incendiary Venus.

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