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What is radiocarbon dating?

At a very steady rate, unstable carbon-14 gradually decays to carbon-12. The ratio of these carbon isotopes reveals the ages of some of Earth’s oldest inhabitants.

See it! Young moon, Venus, Mars

The moon has returned to the evening sky. This week, it’s sweeping past brilliant Venus and fainter Mars. Photos from the EarthSky community, here.

$40 billion a day for solar super-storms

The probability of another event like the 1859 Carrington event is – at any given time – low. But many believe it’s “almost inevitable” one will occur, eventually. A new study explores the risks.

What is a supermoon?

By at least 1 definition, the year 2017 has 4 supermoons. Three are new moons and not visible in our sky. The only full moon supermoon of 2017 will come in December.

Moon near former pole star on January 9

People in Asia will see Aldebaran pass behind the moon on this date. The rest of us will see Aldebaran in the moon’s glare. Plus … the story of Aldebaran when it was part of a double pole star.

Leap second to be added December 31

Delay those New Year’s plans. World timekeepers will add a leap second just before midnight on December 31, 2016.

Drought still grips southern California

California has dry spells, but the state hasn’t had exceptional drought since at least 2000. Now, about 20 percent of California is in exceptional drought, and many trees have died.

Mount Hekla was called Gateway to Hell

Mount Hekla is Iceland’s 3rd most active volcano. A large eruption in 1104 earned it the moniker Gateway to Hell. Is Mount Hekla overdue for another eruption?

See it! Super Hunter’s Moon 2016

Many captured the full Hunter’s Moon last night. It was also the 1st of 3 supermoons in 2016.  Thanks to all who contributed!

Day and night exactly equal at equinoxes?

On the day of the equinox, the center of the sun would set about 12 hours after rising – given a level horizon, as at sea, and no atmospheric refraction.

Supermoons and the Saros cycle

Here’s one you might not know … the intriguing relationship between supermoons and the famous 18-year Saros cycle of eclipses.

Update on Dawn mission to Ceres

The Dawn spacecraft is still orbiting Ceres. It went into an extended mission mode on July 1. Some mission highlights and current thinking, here.

Capricornus? Here’s your constellation

The constellation Capricornus the Sea-goat. How to see it, and how a sea-goat came to reside among the stars.

Today in science: A moon for Mars

American astronomer Asaph Hall discovered Phobos, one of the two Martian moons, on this date in 1877. Did he imagine how well we’d see Mars’ moons today?

Sagittarius? Here’s your constellation

You can see the constellation Sagittarius on August evenings. Look here for the lore and science of this constellation.

Humpback whales, heroes of the sea?

Humpback whales appear to rescue not just their own species, but also other whale species, seals and sea lions from attacks by killer whales.

Parakeet takeover ahead?

“Parakeets are Britain’s fastest growing bird population and are on a trajectory to global domination.”

Eltanin and Rastaban, the Dragon’s Eyes

These two famous stars shine down from the northern sky. Eltanin and Rastaban represent the fiery Eyes of the constellation Draco the Dragon.

Earth-sized aurora on Jupiter

NASA released this image as the Juno spacecraft arrived at Jupiter.

Astronomers find a baby planet

Planet K2-33b resides in a solar system in the process of being born. In human terms, if Earth were 45 years old, this planet would be just a few weeks old.

What is virga?

We’ve all seen virga, but maybe not known what it’s called. Virga is rain that evaporates before it hits the ground. Enjoy these photos!

The secrets of night-shining clouds

People at high latitudes are seeing glowing clouds in a dark night sky. They’re called noctilucent or “night-shining” clouds.

Deciphering mysterious honey bee decline

While the massive and sudden colony collapses that occurred a decade ago have abated, honey bees are still dying at troubling rates.

Virgo? Here’s your constellation

The constellation Virgo the Maiden fully returns to the early evening sky – with her feet planted on the eastern horizon – by early May.

Airplane crosses sun’s face

While preparing on Sunday to watch today’s transit – an event Mercury crosses the face of our sun – Helio C. Vital caught an airplane doing the same.

Milky Way over Arenal Volcano in Costa Rica

“Since three years ago, we have planned to shoot this photo. We went to the zone repeatedly but every time we got nothing … until now.” – Sergio Vindas

Chernobyl all-time worst nuclear accident

The meltdown at the Chernobyl Nuclear Power Plant on April 26, 1986 exposed 572 million people to radiation. It was far worse than the 2011 Fukushima accident.

How can I capture star trails?

As Earth spins under the sky, the stars appear to move. When a camera captures that movement, that’s called a star trail. Plus … an astrophotographer explains how he does it.

An inconspicuous comet

Many hoped Comet 252P/LINEAR would become visible to the eye. It has, but only barely. Enjoy photos from the few, the proud, who’ve captured this comet on film!

Closest new moon of 2016 on April 7

April 7 moon turns new six hours before perigee – closest point to Earth. We won’t see it, but it counts as a supermoon and will affect ocean tides.

This ancient arthropod kept its babies on a leash

Scientists have discovered a tiny 430-million-year-old sea creature – dubbed Kite Runner – that apparently dragged its offspring around on strings like kites.

Closest comet in 246 years via radar

Record-breakingly close flybys of two comets earlier this week. Radar images of one, the closest comet in 246 years. Will the other be visible to the eye?

Come to know Big and Little Dippers

The Big Dipper is easy. And, once you find it, you can find the Little Dipper, too. Plus … learn how the stars of the Big Dipper are moving in space.

First of year’s 6 supermoons March 9

We’ll have six supermoons in 2016. The first one is a new moon supermoon, not visible in our sky.

Lenticular clouds look like UFOs

These lens-shaped clouds are often mistaken for UFOs. Here’s how they form, plus gorgeous photos.

Moons might hold key to finding E.T. life

As the list of known planets beyond our solar system grows, the search for their moons is intensifying. Why exomoons might be key to E.T. life.

See 5 bright planets at once

First time we can see 5 planets at once since 2005. All 5 are up before dawn, still, and all 5 will remain visible until Mercury disappears in the dawn just after mid-February.

See it! All 5 bright planets at once

Best photos from the EarthSky community of the 5 bright planets now visible at once in the sky before dawn. Thanks to all who posted!

Why Planet Nine might be for real

Claims about new planets that turned out to be wrong – and why ‘Planet Nine’ may be different.

2015 hottest year on record, by far

“What we have seen this past year will likely be routine in about 15 years, although regionally the details will vary considerably,” says climate expert Kevin Trenberth.

Best photos of Comet Catalina

Comet C/2013 US10 (Catalina) has been a wonderful target for photographers. See photos of this icy visitor from the depths of space, here. Thanks to all who submitted!

Best photos: Venus and Saturn January 9

A million thanks to you who posted photos on EarthSky pages of Venus and Saturn Saturday morning! Closer than any two planets since 2013 …

Today in science: Earthrise from moon

Click here for a video visualization of events leading to one of the best-known photographs of the 20th century – Earth rising over the moon – as seen by Apollo 8 astronauts.

Using light to simulate time travel

Most work on time travel has focused on its theoretical aspects, but there are also attempts to simulate the effects of time travel experimentally.

Ice loss benefits Adélie penguins, for now

Over the past 14,000 years, penguin numbers in East Antarctica increased 135-fold because of disappearing glaciers and sea ice. How long can populations keep growing?

Weather-related natural disasters are up

With COP21 poised to begin in Paris, a new UN report suggests that weather-related disasters were nearly twice as frequent over the past decade as two decades ago.

Hole-punch cloud over Massachusetts

Hole-punch clouds are sometimes called fallstreak holes. They are often-circular patches of clear sky, surrounded by clouds. Airplanes create them.

Mars’ moon Phobos slowly falling apart

The mysterious grooves on Phobos are likely early signs of structural failure. Scientists expect the moon to be pulled apart in 30 to 50 million years.

Saturday night’s mystery light not a UFO

People in Los Angeles and various states in the U.S. West saw the mysterious light. It was confirmed as a Naval missile test off the California coast.

Update: 2015 TB145 likely a dead comet

Last week heralded as largest known asteroid to pass Earth until 2027. Swept within 1.3 times the moon’s distance on October 31. Now thought to be a comet!