Dreaming of a white Christmas such as the one in this image? You may have to keep on dreaming. Statistics on snow cover from 14 major U.S. cities between 1960 and 2000 show the overall trend on the decline.
In the 1990s, these cities saw 47 white Christmases — which translates to an inch or more of snow on the ground. During the 1960s, by comparison, the 14 major cities saw 72 snowy Christmases, according to Dale Kaiser, a meteorologist at the Oak Ridge National Laboratory who compiled the data. And between 2000 and 2008, only three of the cities on the list — Detroit, Chicago and Boston — showed an uptick in their downward trends.
While statistics from one day of the year are an imperfect gauge of a seasonal climate, Kaiser notes the decline in white Christmases hints at a trend of less snowy winters seen in many parts of the country. Click the "Next" button for nine more gifts of science for Christmas.
— By John Roach, msnbc.com contributor
Virgin birth not unique to Mary
Christmas, traditionally, is a giant birthday bash for Jesus Christ, who was said to be born to the Virgin Mary. The event is considered miraculous: Human biology requires sex for reproduction. But via a process known as parthenogenesis, eggs become embryos without male fertilization. It has been found to occur in about 70 species. Recent additions to the list include komodo dragons, the world's largest lizard; and an Atlantic blacktip shark, shown here.
The science behind the 'Star of Bethlehem'
Some biblical wise men figured that a rare celestial spectacle a little more than 2,000 years ago heralded the arrival of a king, and followed it to where he and his mother lay. But what was this "Star of Bethlehem"?
Astronomers have puzzled over the mystery for years. One idea holds the "star" was actually a rare alignment of planets, several of which occurred between 3 B.C. and 2 B.C. — dates that some scholars think could correspond with the historical birth of Jesus. One such sequence involves the planet Jupiter, seen here, flitting back and forth across the star Regulus in Leo and then approaching Venus so that the two appeared as one.
Frankincense, tapped out
Balthasar, the wise man on the right in this nativity scene, brought the baby Jesus a gift of frankincense, according to the New Testament.
While the fragrant resin may have been abundant in biblical times, today the trees that produce it on the Arabian Peninsula and in the Horn of Africa are about tapped out, according to scientists. Tapped trees, the researchers found, produce fewer and less productive seeds than those left alone for at least four years. And since standing trees are also being cleared for farmland and munched by goats, those that remain standing are under duress. The researchers call for less intensive tapping to keep production sustainable.
Mistletoe: A kiss of death?
Suspended sprigs of mistletoe have kindled and rekindled many a holiday romance over the years, but the parasitic plant can be the kiss of death for trees.
Most mistletoe species make their own nutrients via photosynthesis, but grow on trees where they suck out water and minerals essential to their hosts' long-term survival. And once infected, a tree is stuck with mistletoe until death. The plant itself is spread by birds, which eat the seeds and poop them out on other tree limbs.
A shot of holiday brandy is healthy?
Add a shot of holiday brandy to the list of supposedly sinful consumables that give a healthy kick — in moderation, of course. As studies on red wine, dark chocolate and coffee have previously shown, recent research on brandy found that a shot glass full of the distilled fermented fruit juice contains as much antioxidant potential as the daily recommended intake of vitamin C. The antioxidants, which are chemical compounds that help protect body cells form free radicals, come mainly from copper during the distilling process, according to researchers at Monash University in Australia. Team leader Gordon Troup, a physicist, is shown here holding a glass of the amber liquid.
How science built a 'better' Christmas tree
While Charlie Brown's scraggly Christmas tree had an undeniable charm, most shoppers in the spirit for a natural tree want something that sheds few needles, requires little trimming and is full of hardy branches on which to hang ornaments. Scientists have spent decades doing their best to appease the market. They've selectively bred trees with all the traits desired by those gathered around the hearth as well as things such as disease resistance and fast growth that cheer up accountants focused on the bottom line. The man in this photo is walking among scientifically improved trees on his farm in Maine.
How to track Santa
Around this time of year, millions of children around the world giddily anticipate the arrival of a jolly red-suited man, his reindeer and a sleigh spilling over with gifts. As they wait, they can track Santa's progress as he and his merry crew race around the globe on NORADSanta.org, a Web site maintained by the North American Aerospace Defense Command. While there, visitors can also watch preview videos, play games and listen to holiday music. One page even explains that Santa must function within his own "time-space continuum" in order to complete his deliveries, which could open the door to parent-child conversations about science. This image shows volunteers at Santa tracking HQ answering e-mails and phone calls from interested kids on Christmas Eve.
Falling apart over jigsaw puzzles?
A popular post-presents pastime is the jigsaw puzzle, but what seems like a nice way to keep the holiday spirit together often fragments the peace. Why? Because, according to researchers at the University of Bath, different people approach the puzzle with conflicting strategies. For example, some puzzlers are border-obsessive while others scour the table for matches to a component of the picture on the lid. And those with different strategies tend to compete with each other: hiding sections, hoarding piles of pieces and even pocketing jigsaw pieces all in bid to "win" by placing the final puzzle piece.
The findings are part of a larger program to understand successful collaboration and develop software that will help people collaborate more effectively.
Christmas is for the birds
Every year around the holidays, thousands of people across the Americas step outside armed with binoculars and checklists. The volunteers in this army dutifully count the number and types of birds they see. The results of the annual Christmas Bird Count contribute to what scientists consider one of the best databases available on the distribution and population of many species of birds. It has helped scientists show, for example, that the population of the northern pintail duck, shown here, has dropped 77 percent since 1967.