by Paul D. Maley, NASA Johnson Space Center Astronomical Society


Our Bolivia transit team: left to right, Tom Cave, Byron Braswell, Sheila Stephenson, Sharon Braswell, Karen Hoffman, Leslie Strike, Les Pearce, Chris Faser, Lynn Palmer, Paul Maley.

The earliest passage of the planet Mercury between Earth and the Sun was seen on November 7, 1631 by the French astronomer Pierre Gassendi.  It had to wait for the invention of the telescope in order to be able to detect the transit since it was not visible to the unaided eye.  Back then, the importance of making such observations was to determine the solar parallax but the Gassendi observation provided the first time a quantitative measurement of the apparent magnitude of a planetary disk.  It was Kepler who before his death in 1630 advised astronomers to observe the transits of Venus and Mercury by projecting the image of the Sun onto paper by means of a telescope.  Gassendi observed in a darkened room using a small telescope which projected the Sun onto a piece of paper but because of the huge uncertainty as to what the size of Mercury might look like, he initially thought it was a sunspot. Others as well were taken aback by how small Mercury appeared…about 20 arcseconds in diameter or .022 solar diameters. The observations of the 1631 transit established that the preconceived notion of how large the planets were had to be reevaluated in light of the tininess of Mercury.

Today such transits are more of a curiosity and an interesting sight to see and do not have the scientific benefit.  Even so our expedition to Bolivia was worth it as we had the opportunity to see this event under mostly clear sky at an altitude of 3825m/12556 ft above sea level.


Guide Marcelo Alcon and Paul Maley prepare the transit projection board. A 9-inch Dobsonian was used to project the Sun.  Notice the strings used to slant the board to make it parallel to the eyepiece plane.  Note the blue sky which predominated during our entire May 4-10 trip.  Sheila Stephenson photo.


The initial setup for projection turned out to be difficult to manage because of the wind.  Byron Braswell photo.


An earlier projection board worked much better but the paper wrinkled overnight and the projection plane was not uniform.  A huge crane was erected by the dock and observatory but we were able to get it lowered to avoid interference on transit day and at night. P. Maley photo.

Mercury can be seen as the small dot on the first projection screen. A green cloth was used to help cover the image. Leslie Strike photo.


A cover was placed over the projection screen to increase contrast on the previous day but it was left in the projection plane of the Sun’s image and a hole was burned into the cloth. This emphasizes that any time the Sun is projected, it must be attended to assure no one experiences a hazard to their eyes or accompanying hardware. P. Maley photo.


Byron Braswell prepares for the transit. P. Maley photo.


Les Pearce in action. P. Maley photo.


Karen Hoffman in a break between exposures. The transit lasted 7.5 hours allowing time for lunch and other things. P. Maley photo.


An alpaca grazes adjacent to the observatory at the beginning of the transit. Lynn Palmer photo.

Mercury and two sunspot groupings around noon local time March 9, 2016 from Huatajata, Bolivia. Photo group by C. Faser. Compare this Hydrogen Alpha wavelength view with visual views below. Image taken via 77mm Borg with a 60mm single stack Coronado etalon and a ASI120mm camera; focal length of 500mm and the pictures taken at 1.09 ms.


C. Faser image 2.  Note granulation, filaments and sunspot details.

3rd contact!  C. Faser image 3.

bras1 7.33 AM1

The seeing was quite good during the transit. This photo shows the sunspot groups and Mercury in the last hour before the planet exited the Sun. Byron Braswell photo with Nikon D7100, 850mm fl, f/8, ISO 100, 1/8000 sec. 

Bras5 2.39 PM black drop1

Very close to 3rd contact you  can begin to see the historically reported “black drop effect”. This “tear drop” looking effect currently appears to be a function of a combination of the optics used and solar limb darkening as opposed to an Earth or Mercury atmosphere effect as previously though since this was first spotted in 1761 during a transit of Venus.  Byron Braswell photo.


3rd contact white light image similar to the above with a Meade 2045D, f/10, 1/800 sec exposure at ISO800, Nikon D3100 by P. Maley.  Compared to the H Alpha images above, the orientation of this image is flipped.


At the start of the transit the Sun was very low in the eastern sky and to peer over the trees along the horizon I had to elevate my scope as high as possible. Lynn Palmer photo.


This configuration was thrown together the day before to elevate the Meade scope high enough to catch second contact.  Lynn Palmer photo.


In order to reach the high elevation of the Sun near midday we had to tie the Meade down with bailing wire to the base of a 22-inch Starmaster Dobsonian inside the observatory located at our hotel. P. Maley photo.



A sample of the tasty meals prepared at the Inca Utama Hotel in Huatajata. Lynn Palmer photo.

We traveled a short ways along the infamous Death Road.  Byron Braswell photo.

Llama fetuses hanging in the Witches Market.  Byron Braswell photo.


Trilobite displayed in a local market.  Meaning three lobed, these are extinct hard shelled marine creatures that existed over 520 million years ago, predating dinosaurs. P. Maley photo.
desert costumes_cave1Costumes used for Southern Cross Festival out in the middle of nowhere.  Tom Cave photo.

Bolivian market.  Byron Braswell photo.

A view thousands of feet down into the valley from our high point of nearly 15,000 ft. Byron Braswell photo.


A scene you might expect from Iraq but this is from a village outside La Paz on the way to Huatajata. The corpse is strung up as either a warning to criminals or to scare off people who want to observe future transits of Mercury. Tom Cave photo.

Traveling on the sky gondolas in La Paz. Leslie Strike photo.


Even at 14,000 ft elevation you can see political signs extolling current president Evo Morales. P. Maley photo.

dusk view from hotel roof1_cave

View at dusk from the Casa Grande Hotel in La Paz. Tom Cave photo.


A 30 second exposure with a 14mm lens from Huatajata with Scorpius (above center) and Alpha and Beta Centauri and the southern cross in lower right. P. Maley photo.

The Large Magellanic Cloud in the early evening in this 30 second exposure, ISO1600, f/3.5, 14mm lens. P. Maley photo.

A camera pointed overhead inside the observatory captures a number of geostationary satellites during a 6-minute exposure. P. Maley photo.

The Iridium 12 satellite flares over the hotel at magnitude -4.  Notice the Big Dipper lying flat on the horizon.  P. Maley photo. 


Not to be outdone, an alpaca silhouetted at the observatory views the southern cross.  P. Maley photo.

Incredibly colorful art of Bolivia. Lynn Palmer photo. 

Llama closeup.  Byron Braswell photo.

A boat made of reeds sailing on Lake Titicaca. Lynn Palmer photo. 


Reed boat maker. Leslie Strike photo.


The entrance to Moon Valley. What a terrific area to visit! P. Maley photo.


A herd of vicuna, alpaca and llama. P. Maley photo.


Observatory 1 at Tiahuanaco could date back 14,000 years. View from the top of the Acapana pyramid. Kalasasaya is seen in background.  The purpose of the Kalasasaya was to determine certain important solar alignments. P. Maley photo.


Tihuanaco map.  A complete cycle takes roughly 41,000 years to complete. The alignment of the Kalasasaya temple depicts a tilt of the earth’s axis amounting to 23 degrees, 8 minutes, 48 seconds, which according to astronomers, indicates a date of 15,000 B.C.  The Acapana pyramid lines up perfectly with the cardinal points. 


Observatory 2 at Tiahuanaco.  Sunken temple with the entrance to the Kalasasaya temple in the background right. The Subterranean Temple, was studded with sculptured stone heads set into cut-stone facing walls and in the middle of the court was located a now-famous monolithic ‘Bennett’ stela, Named for archaeologist Wendell C. Bennett who conducted the first archaeological research at Tiahuanaco in the 1930’s, the Bennett Stela represents a human figure wearing elaborate clothes and a crown.  P.Maley photo.