The Pale Blue Dot is an iconic photograph of Earth captured by the Voyager 1 space probe in 1990.

Taken from a distance of around 6 billion kilometers (3.7 billion miles) as Voyager 1 was departing our solar system, the image portrays Earth as a tiny, pale blue speck in the vastness of space.

This pale blue dot image is a powerful reminder of our planet’s isolation and fragility in the cosmic expanse, highlighting the need for responsible stewardship of our home.

The photograph was a result of astronomer Carl Sagan’s suggestion to turn Voyager’s camera back towards Earth, offering a profound perspective on our place in the universe.

We know that an all-out U.S.-Russia nuclear war would be bad. But how bad, exactly? How do your chances of surviving the explosions, radiation, and nuclear winter depend on where you live?

The past year’s unprecedented nuclear saber-rattling and last weekend’s chaos in Russia has made this question timely. To help answer it, I’ve worked with an amazing interdisciplinary group of scientists (see end credits) to produce the most scientifically realistic simulation of a nuclear war using only unclassified data, and visualize it as a video. It combines detailed modeling of nuclear targeting, missile trajectories, blasts and the electromagnetic pulse, and of how black carbon smoke is produced, lofted and spread across the globe, altering the climate and causing mass starvation.

As the video illustrates, it doesn’t matter much who starts the war: when one side launches nuclear missiles, the other side detects them and fires back before impact. Ballistic missiles from U.S. submarines west of Norway start striking Russia after about 10 minutes, and Russian ones from north of Canada start hitting the U.S. a few minutes later. The very first strikes fry electronics and power grids by creating an electro-magnetic pulse of tens of thousands of volts per meter. The next strikes target command-and-control centers and nuclear launch facilities. Land-based intercontinental ballistic missiles take about half an hour to fly from launch to target.

Major cities are targeted both because they contain military facilities and to stymie the enemy’s post-war recovery. Each impact creates a fireball about as hot as the core of the sun, followed by a radioactive mushroom cloud. These intense explosions vaporize people nearby and cause fires and blindness further away. The fireball expansion then causes a blast wave that damages buildings, crushing nearby ones. The U.K. and France have nuclear capabilities and are obliged by NATO’s Article 5 to defend the U.S. so, Russia hits them too. Firestorms engulf many cities, where storm-level winds fan the flames, igniting anything that can burn, melting glass and some metals and turning asphalt into flammable hot liquid.

Unfortunately, peer-reviewed research suggests that explosions, the electromagnetic pulse, and the radioactivity aren’t the worst part: a nuclear winter is caused by the black carbon smoke from the nuclear firestorms. The Hiroshima atomic bomb caused such a firestorm, but today’s hydrogen bombs are much more powerful. A large city like Moscow, with almost 50 times more people than Hiroshima, can create much more smoke, and a firestorm that sends plumes of black smoke up into the stratosphere, far above any rain clouds that would otherwise wash out the smoke. This black smoke gets heated by sunlight, lofting it like a hot air balloon for up to a decade. High-altitude jet streams are so fast that it takes only a few days for the smoke to spread across much of the northern hemisphere.

This makes Earth freezing cold even during the summer, with farmland in Kansas cooling by about 20 degrees centigrade (about 40 degrees Fahrenheit), and other regions cooling almost twice as much. A recent scientific paper estimates that over 5 billion people could starve to death, including around 99% of those in the US, Europe, Russia, and China – because most black carbon smoke stays in the Northern hemisphere where it’s produced, and because temperature drops harm agriculture more at high latitudes.

It’s important to note that huge uncertainties remain, so the actual humanitarian impact could be either better or worse – a reason to proceed with caution. A recently launched $4M open research program will hopefully help clarify public understanding and inform the global policy conversation, but much more work is needed, since most of the research on this topic is classified and focused on military rather than humanitarian impacts.

We obviously don’t know how many people will survive a nuclear war. But if it’s even remotely as bad as this study predicts, it has no winners, merely losers. It’s easy to feel powerless, but the good news is that there is something you can do to help: please help share this video! The fact that nuclear war is likely to start via gradual escalation, perhaps combined by accident or miscalculation, means that the more people know about nuclear war, the more likely we are to avoid having one.

TIME/Max Tegmark. Tegmark is a professor doing AI research at the Massachusetts Institute of Technology

Here’s What to Do About germs on your cell phone

Most people don’t give a second thought to using their cell phone everywhere, from their morning commute to the dinner table to the doctor’s office. But research shows that cell phones are far dirtier than most people think, and the more germs they collect, the more germs you touch.

In fact, your own hand is the biggest culprit when it comes to putting filth on your phone. Americans check their phones about 47 times per day, according to a survey by Deloitte, which affords plenty of opportunities for microorganisms to move from your fingers to your phone.

“Because people are always carrying their cell phones even in situations where they would normally wash their hands before doing anything, cell phones do tend to get pretty gross,” says Emily Martin, assistant professor of epidemiology at the University of Michigan School of Public Health. Research has varied on just how many germs are crawling on the average cell phone, but a recent study found more than 17,000 bacterial gene copies on the phones of high school students. Scientists at the University of Arizona have found that cell phones carry 10 times more bacteria than most toilet seats.

Human skin is naturally covered in microbes that don’t usually have any negative health consequences, and that natural bacteria, plus the oils on your hands, get passed on to your phone every time you check a text or send an email. It follows that most of the organisms found on phones are not pathogens that will make you sick, Martin says. Staphylococcus might be present, for example, but it’s not typically the kind that will give you a staph infection.

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But some bacteria should concern you. “We’re not walking through a sterile environment, so if you touch a surface there could be something on that,” says Susan Whittier, director of clinical microbiology at New York-Presbyterian and Columbia University Medical Center. “There are lots of environmental contaminants.”

Studies have found serious pathogens on cell phones, including Streptococcus, MRSA and even E. coli. Just having these microbes on your phone won’t automatically make you sick, Whittier says, but you still don’t want to let them enter your system. Viruses can also spread on phones if one person is sick with strep throat or influenza and coughs on their cell phone before handing it off to a friend.

Fortunately, there are easy ways to avoid some germs. One of the worst places to use your phone is in the bathroom, Martin and Whittier both agree. When toilets flush, they spread germs everywhere, which is how phones end up with fecal bacteria like E. coli. “Taking a cell phone into the bathroom and then leaving with it is kind of like going in, not washing your hands and then coming back out,” Martin says. “It’s the same level of concern.”

Keeping your phone out of the bathroom will help, but if you want to clean your phone, a few different methods will work. Many people just wipe their phones with a soft microfiber cloth, which will remove many of the germs. For a deeper clean, Whittier recommends using a combination of 60% water and 40% rubbing alcohol. Mix the ingredients together, and then dip a cloth in the solution before wiping it gently across your phone. Unless you’re sick, doing this a few times each month is plenty, Whittier says. Stay away from liquid or spray cleaners, which can damage your phone.

Still, the best advice has more to do with you than the phone. Wash your hands several times a day, the experts say, and you’ll likely be just fine.