Earth was 88 million miles from Mars - nowhere near the closest possible distance between our two worlds - when the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter took this image.

Notice the clouds on the Earth image. NASA scientists say they could make out the west coast outline of South America at lower right, but I couldn’t see it. These scientists also pointed out that Earth’s clouds are so bright, in contrast to our dull gray moon, that the color image of Earth required a fair amount of processing to make a nice-looking release. The moon image has been brightened relative to Earth for this composite.

So that’s the Earth and moon from Mars. Want to see Mars with your own eyes from Earth? Try this chart.

Image credit: NASA/JPL-Caltech/University of Arizona

Original source: Earth and moon seen from Mars from NASA

So says the United Kingdom’s World Cancer Research Fund, whose website carries the tagline “pioneers in cancer prevention.”

The WCRF UK examined 7,000 existing studies over six years to create what they call “the most comprehensive investigation ever into the risks of certain lifestyle choices.”

The result? According to the WCRF UK, everyone should aim to be as thin as possible without becoming underweight, in order to decrease the risk of cancer.

The Body Mass Index (BMI) is a calculation which takes into account height and weight. A BMI of between 18.5 and 25 has been considered a “healthy” weight range. But the new report says that risk increases as an individual heads towards the 25 mark, and that “everyone should try to be as close to the lower end as possible.”

The WCRF UK report includes more specific recommendations for cancer prevention.

Limit red meat
Limit alcohol
Avoid bacon, ham, and other processed meats
No sugary drinks
No weight gain after 21
Exercise every day
Breastfeed children
Do not take dietary supplements to cut cancer

These are recommendations, say the report’s author’s, not commandments. For the most part, I like them and agree with them. They sound sensible. We all know that it isn’t healthy to be overweight, and, unless you’ve been living on the moon, you know that obesity has become a critical public health problem in the U.S. and the rest of the developed world.

But no weight gain after 21? Right.

I have to wonder if this report took the difference between male and female physiology into account. To me, older women look better - healthier - when they are a little heavier. I know I feel in many ways stronger now - with a few extra pounds - than I did when I was my daughters’ ages (24 and 27) and very thin. I have a BMI of 24.2, by the way. Getting down “as close as possible” to a BMI of 18.5 would require me to go back to the weight I had at age 12.

What’s more, thinness is a risk factor for osteoporosis, the disease in which the bones of older women (and men) become less dense and break more easily. My grandmother was one of many women of her generation who died after breaking a hip and, essentially, never getting up again. According to the National Osteoporosis Foundation website, bone structure and body weight do play a role in osteoporosis, with “small-boned and thin women (under 127 pounds) … at greater risk.” Plus, we older women like to remind each other that fat cells hold a little estrogen, with its ability not only to protect the bones but also to relieve menopausal symptoms.

As the BBC article points out, many cancers are not thought to be related to lifestyle. But the report’s authors say that - of the 10 million cases of cancer diagnosed across the world each year - perhaps three million could be prevented if the recommendations were followed. Saving three million lives would be a good thing. On the other hand, you could always deny yourself red meat, alcohol and so on, become very thin … and still get cancer.

The WCRF UK study is interesting. But, knowing a bit about Asian thought, I’ll stick to the advice of the ancient Chinese philosophers: practice moderation.

Read the BBC article: Be thin to cut cancer, study says

Read the full report from the United Kingdom’s World Cancer Research Fund

Photo credit: Thou Shalt Have No Other Food Before Me image by Flickr user Frengo. Used with permission.

And he’s off to a great start, with an interesting turn of phrase, a new way of thinking about global population, in a post that he calls the population cluster bomb. The idea is that Earth’s population isn’t moving in the direction suggested by the 1960s book by Paul Ehrlich titled The Population Bomb … which presented the essentially Malthusian idea that world population would keep growing and growing and GROWING toward catastrophe. I was there in the 1960s, and I remember holding The Population Bomb in my hands and believing it, as many did … but I was wrong.

Instead, as Revkin points out:

What (population experts now) depict is more like a dangerous scattering of cluster bombs, as the world splits into two types of countries: those with aging, shrinking populations, like Japan and much of Europe, and those regions, like most of Africa and parts of south Asia, still mired in poverty, disease, illiteracy or government dysfunction with resulting high birth and death rates.

In other words, some countries’ populations are expected to keep increasing, while others decrease. Overall, the rate of population growth - across the entire Earth - continues slowing down so that, by the time our children’s children arrive at the year 2100, the overall number of humans on Earth should be even smaller than now. When I first heard this idea, it surprised me. A shrinking world population? This possible outcome (surely, no one knows what will happen) is something that I - in my teens, reading Ehrlich’s book - never contemplated. World population may stabilize.

The idea of a population cluster bomb (what a great description) means that, despite ourselves, birthrates are already falling in some places on Earth, if not in all. Why not all? Because the key for falling population rates seems to be wealth and urbanization. As nations become wealthier and more urbanized - as people forsake the agricultural lifestyle for cities - they apparently begin to think that two children are enough. Women play a pivotal role, because as women become more educated, become wage-earners, have more power within the family and ultimately take our places alongside men as true equals, most women opt to have fewer children.

Revkin spends most of his blog post on the population cluster bomb speaking with demographer and sociologist Joseph Chamie of the Center for Migration Studies. It’s a fascinating interview. Check it out.

In the meantime, tell me what you think. Do you agree with population experts? Will Earth’s population be able to stabilize by the end of this century? And, if it does, what sort of world will that be?

Photo credit: Thanks to the European Parliament which points out that many people want to have their say.

This comet has become an amazing sight, even in urban skies. The comet is easily visible to the eye alone. I spotted it easily both Friday and Saturday nights this weekend while walking in downtown Austin, Texas, a city of nearly one million inhabitants. How can you recognize it? Unlike some comets, Comet Holmes doesn’t have a tail. It’s a round fuzzball of a comet … distinctly not a star. It’s in the northeast in the evening and, as long as you’re in the northern hemisphere, it’s visible somewhere in the northern sky throughout the night. Just look! Look for the round fuzzy object that doesn’t look like a star.

For more detailed instructions on how to spot it, check out this article: A Halloween comet and a ghoul star.

I’m pretty sure that if I showed this comet to my 24-year-old daughter, Joni, she’d be unimpressed. No long, dramatic comet tail. No explosions. No real-time brightness surges, optimally with sound effects … whaaaaooo, whaaaoooo …

Nothing but a silent fuzzball, bright enough to see in city skies.

And yet to me - maybe to all of us who watch this skies - this is a wonderful event. The sky changes with the seasons, the planets brighten and dim, the moon waxes and wanes on its monthly journey across the heavens. The sky is ever-new to me, but there’s also something changeless about it, a sameness, a familiarity, like an old friend. So when something like this happens - a comet visible to the eye where no comet was before - it tugs at the heart.

People who watch the skies with telescopes see comets all year long. We who watch with just our eyes see them come and go in our skies, with years in between naked-eye comets. Our ancestors saw comets as omens. We know them as mysterious visitors from the deep freeze of the outer solar system, and we send our spacecraft to land on them and probe their icy surfaces. We know they become visible to us only when they swing in toward the sun - some every few years, some only once in thousands of years - and that the characteristic comet tail comes from ices and dust boiling off their fragile surfaces as they draw near the sun.

Most comets are faint. I don’t recall a comet like Holmes that has brightened so much, so fast. Comets tend to brighten gradually as they draw near the sun that binds us and them in orbit. On this return trip near the sun, Comet Holmes had been watched by astronomers with telescopes since July of 2007. Then, on October 24, it just went pop into easy visibility. Now you don’t see it. Now you do.

Don’t miss this one.

Photo credit: Joe Zajac and the Harvard-Smithsonian Center for Astrophysics.

A Halloween comet and a ghoul star

Comet reports and images from the Harvard Smithsonian Center for Astrophysics.

Comet reports and images from Spaceweather.com

17PHolmes from Gary Kronk, comet expert.

Realize that 2 billion is a mind-bogglingly large number. The global population is now about 6.6 billion, with 9 billion expected by 2050.

The question posed by the PRB is whether India will reach a population of 2 billion by 2100 … but realize that by then world population will probably have dropped, with some countries losing as much as 40% of their populations as soon as 2050, according to an earlier PRB study. So if India has a 2 billion population by 2100, does that mean this single land area - only 2.4% of the total land area on Earth - will have more than one-third of Earth’s inhabitants? According to the PRB’s recent report (pdf), India may or may not reach a population of 2 billion by 2100. So, clearly, we’re on speculative ground here. Still, the possibilities are … strange for the future world.

The CIA World Factbook reports that India has a population of approximately 1,129,866,154 people, according to a July 2007 estimate. It’s already the world’s second-most-populated country next to China. The earlier PRB study - described in this BBC article from 2004 - suggested that India will overtake China in population in this century. That would make India the country on Earth with the biggest population.

The culprits in this impending population boom in India are young Indians alive today, under the age of 15. This group represents something like 30% to 40% of people in India. Imagine them at child-bearing age - and their offspring to come - populating India’s future. In other words … tick, tock.

India now supports about one-sixth of the world’s entire population, and India has 32 cities with a population over 1 million. That’s in contrast to only 9 cities for the U.S. with a population over 1 million. And, again, India’s inhabitants and their cities occupy only 2.4% of the world’s land area, a land area that is hemmed in on top by the mighty Himalayas.

Carl Haub of the Population Reference Bureau answered questions about India’s population online last week. He pointed out that India’s population is being controlled somewhat now, since a population policy instituted in 1952. He said that, in most Indian states, the child-bearing rate for women is now less than 3 children. But there is still a large rural population in India, and Haub said ” … sadly, many women in rural areas have little say on their own childbearing.”

With increasing population, India’s demographics are destined to change. The population should shift increasingly into cities, as has happened elsewhere on Earth. A more urban world is a less populous world, since children are not needed to work on farms.

Among other things, Haub said:

Societies in the south of India are very different from the north.

Son preference is deeply-rooted for reason of support in one’s old age and to officiate at one’s funeral.

Providing really effective reproductive health information and services in the villages, trying to involve men, and providing non-agricultural jobs in certain states should help fertility rates drop.

India’s fertility rate is actually declining now, although slowly.

By the way, don’t forget that India is not far behind China now in having the world’s largest population, with the U.S. is a distant third. India and China both have populations of over a billion already. The U.S. population is just over 300 million. When will India overtake China in leading global population? No one knows, of course, but many online sources seemed to agree it could happen by 2050, or sooner.

The portrait of India’s burgeoning population seems very poignant to me partly because, in recent years, I’ve become a big fan of novels from India. If you haven’t read A Suitable Boy by Vikram Seth or A Fine Balance by Rohinton Mistry, you should. Almost as deeply as if you had visited, these works of fiction reveal an emotional quality to India, a quality of color and tradition, quiet humor and passion, ancient gods, family, a stratified society where rich, middle class and poor people still seem to encounter each other.

Maybe that’s because India is so crowded.

Picture credits: Mosaic and Taj Mahal by Flickr user foxypard4. Population map of India from Wikipedia Commons.

Read more:

Will India’s Population Reach 2 Billion?

World Fact Book entry on India.

“The harm to water quality could be considerable, and water supply problems at the regional and local levels could also arise,” according to the report, which is titled Water Implications of Biofuels Production in the United States. It was written by a committee of the National Research Council that examined policy options and looked at new agricultural techniques and technologies that could help minimize the effects of biofuel production on water resources.

As oil prices have increased, corn ethanol production has expanded dramatically, and there is high interest in further expansion over the next decade, says the report. For example, in the 2007 State of the Union address, President Bush called for the production of 35 billion gallons of ethanol by 2017, which would equal about 15 percent of the U.S. liquid transportation fuels.

The National Research Council committee looked at how shifts in the nation’s agriculture to include more energy crops - and potentially more crops overall as population rises - could affect water management and long-term sustainability of biofuel production.

The committee found, for example, that the quality of groundwater, rivers, and coastal and offshore waters could be impacted by increased fertilizer and pesticide use for biofuels. It also noted that agricultural shifts to growing corn and expanding biofuel crops into regions with little agriculture - especially dry areas - could “change current irrigation practices and greatly increase pressure on water resources in many parts of the United States.” According to the report …

Water demands for drinking, industry, and such uses as hydropower, fish habitat, and recreation could compete with, and in some cases, constrain the use of water for biofuel crops in some regions. Consequently, growing biofuel crops requiring additional irrigation in areas with limited water supplies is a major concern.

As for non-corn ethanol (for example, ethanol made from switchgrass and native grasses), the report noted that there are “fundamental knowledge gaps” that prevent making reliable assessments about those crops’ impact on water resources.

What are the new technologies and techniques that could prevent ethanol production from impacting water quality and availability? While difficult to predict all future technologies, the report mentioned that, for example, genetically modified crops might use less water and/or fewer pesticides.

Read a news release from the National Research Council.

Find the full report.

The polar bears destined for extinction are those living in Alaska and Russia. The Anchorage Daily News reported that only a tiny surviving population will remain on islands in the Canadian Arctic.

According to the report, a science team spent six months intensively analyzing both existing and new data on polar bears and their habitat. The team documented the direct relationship between the presence of Arctic sea ice and the survival and health of polar bears. Polar bears depend on sea ice as a platform to hunt seals, their primary food. But sea ice is decreasing throughout their Arctic range due to climate change. Their conclusion?

Models used by the USGS team project a 42 percent loss of optimal polar bear habitat from the Polar Basin during summer, a vital hunting and breeding period, by mid-century.

The report also suggests that there is nothing humans can do to save the bears, because efforts to control greenhouse gas emissions and limit hunting and gas development cannot outweigh the effects of habitat loss.

Read more: Could penguins and polar bears swap habitats?

Bird flu - also known as avian flu, or the H5N1 virus - has made fewer headlines in the past year, in contrast to previous years. The other day I found my own downloaded version of the (pdf) Bird Flu and You Preparedness Planner and had a moment of unease when I realized I never got around to making any of its suggested preparations. A global pandemic, after all, is not an if. It’s a when. Experts agree there will be another pandemic, at some point in the future. Whether bird flu will be the specific cause of that pandemic is unknown. Also unknown is how the pandemic will affect people around the world, although it’s safe to assume that the weak, the old, and the very young will suffer most.

Earth & Sky has also presented information on bird flu over the past few years. Here are a few of our radio shows and articles on the subject:

Pandemics always part of human history

Avian flu originates where wildlife meets livestock

How bird flu becomes human flu

Is bird flu the only global pandemic threat?

Bird flu and you

Meanwhile, at a May 3, 2007 political debate, three of the 10 Republican candidates for the 2008 Presidential bid — Kansas Sen. Sam Brownback, former Arkansas governor Mike Huckabee and Rep. Tom Tancredo (Colo.) — said they do not believe in evolution. Two years earlier, a 2005 poll by the Pew Trust showed 42% of respondents (the American people this time) expressing a belief that humans and other animals have existed in their present form since the beginning of time.

Now two pyschologists at Yale - Paul Bloom and Deena Skolnick Weisberg - have presented a paper in Science called Childhood Origins of Adult Resistance to Science. You need a subscription to read the full text in Science, but you can find a great and lucid summing-up piece from Bloom and Weisberg themselves in Edge: Why Do Some People Resist Science?

Apparently, resistance to science is not only about stakeholders protecting their interests.

Bloom and Weisberg report that resistance to science will arise in children when scientific claims clash with early emerging, intuitive expectations. They say this resistance will persist through adulthood if the scientific claims are contested within a society, and will be especially strong if there is a non-scientific alternative that is rooted in common sense and championed by people who are taken as reliable and trustworthy.

By the way, that 2005 Pew poll produced the illustration above. That poll came from the Pew Forum on Religion and Public Life. There’s some very interesting reading there as well.

This idea won this year’s Next Generation award from Metropolis magazine. According to the magazine, “the proposal for lunar-resonant streetlights captured the jurors’ imaginations with an inspiring combination of poetry and practicality.”

Who can argue with that? I remember a night decades ago - while visiting in Colorado - when I traveled with a friend by motorcycle from one small mountain town to another, around the time of a full moon. For part of our journey, my friend switched off the motorcycle’s headlights, and we traveled along that lonely road, with the road ahead and the landscape all around flooded by bright moonlight. It was more than beautiful. It was enchanting. I’ve never forgotten it.

As a stargazer, I know how much light the moon can add to the sky and how much it can cast on the ground. And I know how much the moon’s brightness can vary. At a first quarter or last quarter moon, for example, when the moon is in the sky for only half the night, it’s easy (if you’re in a place not hindered by streetlights) to notice how much the moon illuminates the landscape.

By the way, the designers say that lunar-resonant streetlights “could save as much as 80–90 percent of the energy used in streetlighting …”

And of course there’s the issue of crime. Does bright urban lighting help prevent crime? I know that outdoor lighting helps me feel safe. But among astronomers - who for decades have struggled with the issue of light pollution - it’s sometimes said that outdoor urban lighting doesn’t really increase our safety. Instead, it only makes us feel safe. Also, consider the first comment on the article about lunar-resonant streetlights. Joan Soo said:

Is it in your plan to have the wavelength of the street lights be the same wavelength as moonlight, or at least the color of the ambient light during civil twilight? Our bodies are designed to respond to light at civil twilight wavelengths by slowing down and preparing for rest. Serotonin begins its cascade into melatonin. We sleep. If uninterrupted by the day-wave-length bathroom light or continually assaulted by the street light outside, some of the melatonin eventually cascades into dopamine. This is really good thing. Wouldn’t it be wonderful if crime and violence rates went down with your lighting plan; because, people were getting enough of the right kind of sleep?

I don’t know about that.

But I do know that often now - while moving around at night in my city, with artificial lights glaring from every direction - I remember that moonlit drive across a lonely mountain road from so many decades ago. I hope I’ll live to see lunar-resonant streetlights come to my hometown.