Under cool, gray skies billions watched from outside Westminster Abbey and on television worldwide as 1900 invited guests inside witnessed as Prince William and his longtime girlfriend Kate Middleton were married in one of the largest events in London in decades. A little over an hour after they arrived at the Abbey to be married, the couple emerged on a red carpet and onto the streets to a peal of bells and into a horse-drawn carriage, heading toward Buckingham Palace. The prince had married what the British call a commoner; now the Duke and Duchess of Cambridge (titles granted by Queen Elizabeth II). The couple stepped out onto a balcony a short time later to greet the enormous crowd along the Mall - a tradition at royal weddings. They kissed for the first time in public as a married couple as a cheer went up from the crowd. -- Paula Nelson (36 photos total)

Over 200 are dead after over a hundred separate tornadoes left a trail of destruction across five states in the American South. The nation appears headed for a record number of tornadoes this year. The Federal Emergency Management Agency has been mobilized to deal with the aftermath. Tornado watches were issued for the entire East Coast as the storm system that caused the destruction yesterday moved to new ground. -- Lane Turner (23 photos total)

An estimated 2 billion people around the world are expected to watch live as England's Prince William marries commoner Kate Middleton this Friday at Westminster Abbey. Tourists have flocked to London, decorations are appearing, commemorative memorabilia are for sale, and the armed services are preparing for their role in the big event. -- Lloyd Young 34 photos total)

On April 26, 1986, reactor number four at the Chernobyl nuclear power facility in what is now Ukraine exploded. The largest civil nuclear disaster in history led to mass evacuations, and long-term health, agricultural, and economic distress. The nearby city of Pripyat has been abandoned, and a 19-mile radius "exclusion zone" established where radiation contamination makes continued habitation dangerous. Collected here are archival pictures of the catastrophe, as well as more recent images of the area. In addition, two photographers who've made extensive studies of the aftermath have been gracious enough to share their work with us here. Diana Markosian documented the lives of pensioners Lida and Mikhail Masanovitz, who continue to live in the abandoned ghost town of Redkovka, Ukraine. Her work is found here in photographs 13 through 16. Michael Forster Rothbart has produced one of the most extensive records available of life near Chernobyl. His work is found here in photographs 23 through 29. Links to the websites of both photographers can be found below. -- Lane Turner (34 photos total)

What is the cost of spilling almost five million barrels of oil into the ocean? How do you measure that cost? In GDP reduction? In lives affected? In environmental impact? And how do you measure the cost when long-term effects are impossible to calculate yet, and when a significant portion of the spilled oil is still unaccounted for? One year since the Deepwater Horizon platform exploded, killing 11 workers, there are measurable effects, and many more unknowns. Collected here are pictures of the disaster, recent images of people affected by the spill, and views of the cleanup. Pictures #4 through #10 show areas of shoreline both immediately after the spill and the same area a year later. Click on the picture to see it change from the 2010 view to the present. [See also: The Big Picture: Oil reaches Louisiana shores, May 24, 2010] This effect requires javascript to be enabled. -- Lane Turner (36 photos total)

Getty Images Photographer Chris Hondros, 41, was mortally wounded Wednesday in Misurata, Libya, not long after filing intimate, striking images of the fighting between rebel and government forces. Tim Hetherington, the director and producer of the documentary "Restrepo," was killed in the same attack. While Hetherington's photos were not available to us, we honor both his and Hondros' intense commitment to creating inspiring, touching, storytelling images with this post. The images that follow were made by Hondros in Misurata, Libya, the last three days of his life. Hondros and Hetherington will be missed by colleagues and millions worldwide who have been impacted through simply seeing their work. -- Paula Nelson (39 photos total)

Cuba this week concluded two events, one looking back, and one - ostensibly - looking forward. The 50-year anniversary of the Bay of Pigs invasion was observed with parades and speeches. Victory in the three-day war against a covert US operation to overthrow Fidel Castro, the then-new leader of revolutionary Cuba, is celebrated every year. But 50 years on, a stagnant economy and calls for political reform from a younger generation were an undercurrent during the first party congress in 14 years. What real change will come, and when, remains to be seen. Collected here are some archival images, scenes from the congress and political process, and daily life on the island. -- Lane Turner (31 photos total)

Readers and picture editors view the pictures of conflict in safety and comfort. But for the soldiers fighting the wars, and the civilians caught up in them, conflict is anything but safe and comfortable. We are witness to their stories and tragedies thanks to people who willingly put themselves into the same lines of fire as the protagonists - photographers. Covering conflict has always been dangerous, and many famous photojournalists have given their lives doing it. Robert Capa, Larry Burrows - the list is awful and endless. But lately several incidents have made it seem like the dangers have increased. Land mines have seriously wounded photographers in the past few years. Two photographers for the New York Times, Lynsey Addario and Tyler Hicks, were taken prisoner with their writing colleagues for several days in Libya, and were beaten and abused. Other photographers have gone missing as well, such as Khaled al-Hariri, Roberto Schmidt, Joe Raedle, and Altaf Qadri. All are safe now. The same cannot be said for Sabah al-Bazee, who was killed in in an attack on a government building in Tikrit, Iraq. The Big Picture relies on the willingness of these photographers and others to place themselves in harm's way for our benefit, and I'd like to thank them here for that. Knowing too well that there are others like them, I've assembled a few photographs of recent work (where possible) by the above-mentioned photographers. -- Lane Turner (37 photos total)

Yemen is a poor, deeply divided country in turmoil since January 2011, when mass demonstrations called for President Ali Abdullah Saleh to resign. Saleh has been in power since 1978. Demonstrations have continued for months and Saleh's support has crumbled as some army commanders and tribal leaders have called for his ouster. On April 7, an organization of oil-rich Persian Gulf states joined the increasing number of international voices calling for a transfer of presidential powers. Protests and deadly clashes continue daily with security forces and rival military factions allied with the government and the rebels. More than 100 protestors have died since the turmoil began. -- Paula Nelson (28 photos total)

Japan is just in the beginning of the long term recovery effort from the earthquake that struck off northeastern Japan on March 11. The crisis alert level from the damage to the Fukushima Nuclear Power Plant has now been raised to the highest level of impact, the same as the Chernobyl Russia incident 25 years ago. Searchers continue to look for the dead, displaced Japanese live in shelters, protests continue over use of nuclear power, Japan's economic engine may be disrupted, the massive cleanup of debris is just underway, aftershocks are feared and many continue to mourn those who were lost. The photos collected here are from one month to the day of the quake and beyond. -- Lloyd Young (36 photos total)

Each day, wire service photographers from around the world file photos to their member papers that fall under the category of "daily life." On February 8, 2011, I posted a Big Picture that featured some photography from Pakistan under that heading. The images document what we call in newspaper terminology, "slice of life" photography. They are ordinary, random moments captured around a city or in the countryside and they give us just a glimpse of something in that particular place that we might not ordinarily be able to experience. The images in this post are by photographers from the Associated Press based in China. Again, they contain very little caption information and are intended to provide a small window into another culture perhaps far from our own yet reflecting elements of universality. (Note: These images were collected over the first three months of 2011.) -- Paula Nelson. (34 photos total)

Mass graves. Dismembered corpses. Entire towns besieged. Macabre visions grow in depravity as the drug war in Mexico drags on. Since President Felipe Calderon began using the army to contain the violence four years ago, rival gangs have escalated their turf battles over smuggling routes, and 35,000 lives have been lost, half of those in just the three northern states of Chihuahua, Tamaulipas and Sinaloa. The drug criminals have expanded their shadow by intimidating police forces, using kidnapping and extortion, trafficking migrants, and even pirating oil from Mexico's national oil company, Pemex. Of course, calling this issue "Mexico's drug war" is inadequate. Much of the drug product is destined for the United States, and by some estimates, over $20 billion flows south annually to pay for it. Guns made in the U.S. cross the border as well. The last 16 pictures in this entry were made by Nadav Neuhaus, who was gracious enough to share them with us. Neuhaus spent two years visiting Mexico documenting the drug war. You can see more of his work by clicking on the link below. -- Lane Turner (36 photos total)

The spring equinox was March 20 this year, determined by the changing sunlight and how the earth is tilted and orbits the sun. But we don't need to look to the skies to know the seasons are turning. All we have to do is glance more earthbound to find flashes of color and bursts of life. Flowers are appearing in all kinds of places since the equinox. -- Lloyd Young (27 photos total)

Only soccer rivals cricket in transcending the world of sport to become a deeply felt expression of culture. And in cricket-mad South Asia, a frenzy of feeling for the game burst open for the past two months as the Cricket World Cup 2011 was played out in host countries India, Bangladesh, and Sri Lanka. Fourteen nations participated in the tournament, and the semifinals featured what is arguably the world's most heated sports rivalry: India vs. Pakistan. Collected here are pictures from the past few months of people playing, watching, and living cricket in several countries in South Asia. -- Lane Turner (47 photos total)

Every month in the Big Picture, we revisit Afghanistan, to see the people, to see our troops and troops from other nations, to get a sense of the country. President Hamid Karzai said recently his security forces will soon take charge of securing seven areas around Afghanistan, the first step toward his goal of having the Afghan police and soldiers protecting the entire nation by the end of 2014. Our troops are due to begin coming home this July. There is still work to be done. Many of the photos featured in this post show the celebration of the Afghan New Year. The festival to celebrate new year's starts on March 21 and is celebrated in Turkey, Central Asian republics, Iraq, Iran, Azerbaijan, as well as war-torn Afghanistan and it coincides with the astronomical vernal equinox. One of the most popular places to bring in the new year, Mazar-i Sharif, attracts hundreds of thousands of Afghans. -- Paula Nelson (35 photos total)