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January 1, 2015 sunset by Helio de Carvalho Vital.  Shot 3 of 6.

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.

The last eclipse of the Moon visible from the USA occurred on the night of Sept. 27/28, 2015. It was a total eclipse as the Moon passed completely inside Earth’s dark umbral shadow. ©2015 by Fred Espenak.

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.

The strange mountain on dwarf planet Ceres, called Ahuna Mons.

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.

Capricorn-Large

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.

Phobos, via Viking 1.  Image Credit:  NASA

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?

Photo by Jack Fusco

Perseid meteors: All you need to know

Perseid meteor shower peak was predicted for the morning of August 12. If you missed it, watch for meteors in a country sky between midnight and dawn Saturday morning.

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Sagittarius? Here’s your constellation

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

Flickr user Mark Gunn caught this humpback whale in Monterey Bay, off the coast of California, on March 27, 2016. He said the whale's flukes (tail) spanned 15 feet (4.5 meters).

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.

Image via Sarah2 / shutterstock / theconversation

Parakeet takeover ahead?

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

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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.

The extra second - or leap second - is added to world clocks one second before midnight, UTC.

2016 will have a leap second

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

Image via NASA

Earth-sized aurora on Jupiter

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

Artist's concept of young planet K2-33b, via NASA/JPL-Caltech.

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.

Virga over Golden Open Space, New Mexico on June 1, 2016. . 6:09 pm. Photo via Jay Chapman.

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!

EarthSky Facebook friend Jüri Voit Photography wrote on May 30, 2016: "Season of noctilucent clouds is open!"

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.

Working bee colonies. Image via Elina L. Nino

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.

Classical illustration of the constellation Virgo the Maiden, via constellationsofwords.com

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.

Photo taken May 8, 2016 by Helio C. Vital.

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.

Photo taken April 11, 2016, in La Fortuna de San Carlos, Costa Rica, by Sergio Vindas. Visit Sergio online.

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

Health effects of the Chernobyl disaster are still felt 30 years on. Photo credit: Garanich/Reuters

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.

Montauk Point lighthouse. Photo: Neeti Kumthekar

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.

You can see a faint tail for Comet 252P/LINEAR in this photo taken April 3, 2016 by Michael Jaeger. Used with permission.

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!

When you see the sun on April 7, think of the moon, too.  It'll be between us and the sun - but not exactly between - crossing the sky with the sun throughout the day. Image via Flickr user Nigel Howe.

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.

Image credit: D. Briggs, D. Siveter, D. Siveter, M. Sutton, and D. Legg

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.

Radar images of comet P/2016 BA14 were taken on March 23, 2016, by scientists using NASA's Goldstone Radar in California. At the time, the comet was about 2.2 million miles (3.6 million kilometers) from Earth. Image via NASA/JPL-Caltech/GSSR

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?

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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 cloud, by Chris Walker, 2008

Lenticular clouds look like UFOs

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

If you’re looking for life, you’d do well to look for some moons. Image credit:  Maxwell Hamilton/Flickr

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.

From late January, and through mid-February, 5 bright planets were visible at once in the predawn sky. This image is from February 8, 2016.  It's by Eliot Herman in Tucson, Arizona.  View on Flickr.

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.

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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!

planet-nine

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

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.

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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!

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Moon hides bright Aldebaran tonight

Moon passes in front of, or occults, bright star Aldebaran tonight as seen from N. America, and parts of Europe and Africa. Plus … Aldebaran as part of a double pole star.

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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 …

Photo by Rebecca Lacey in Cambridge, Idaho

Supermoons of 2016

Are supermoons hype? In our opinion … no, just modern folklore. And they cause real physical effects, such as larger-than-usual tides.

Earthrise via Apollo 8 astronauts in 1968

This date in science: Earthrise

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

A green laser reflecting through glass. Credit: Astroshots42 on Flickr/ One Universe at a Time.

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.

Photo credit:  University of Minnesota

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?

Image source: thevane.gawker.com

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.

View larger. | Patricia Evans captured this hole-punch cloud on November 21, 2015.  She wrote: "I spotted this rare punch-hole cloud this afternoon from the parking lot of a restaurant in Chelmsford, MA.  Since I always carry my camera with me, I was able to take this shot!  This is only the second punch hole cloud I've ever seen.  The first one was just a few miles away from this spot five years ago... in 2010!  Canon SX50HS - ISO 80  f/4.5 1/1000 sec."

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.

New modeling indicates that the grooves on Mars’ moon Phobos could be produced by tidal forces – the mutual gravitational pull of the planet and the moon. Initially, scientists had thought the grooves were created by the massive impact that made Stickney crater (lower right). Image via NASA/JPL-Caltech/University of Arizona

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.

Hole-punch cloud image provided by Andrew Heymsfield.  Used with permission

Hole-punch clouds are made by jets

It might look like a UFO – but it’s really a hole-punch cloud. A word about the classic connection between hole-punch clouds, jets and snowfall.

Mysterious light sailing across the sky on Saturday night, widely seen across the U.S. West.  This image is a still from a video (profanity alert!)

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.

This image of asteroid 2015 TB145, a dead comet, was generated using radar data collected by the National Science Foundation's 1,000-foot (305-meter) Arecibo Observatory in Puerto Rico. The radar image was taken on Oct. 30, 2015, and the image resolution is 25 feet (7.5 meters) per pixel. Image credit: NAIC-Arecibo/NSF

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!

Binoculars are the perfect stargazing tool

Top 6 tips for using ordinary binoculars for stargazing

If you’re a beginning stargazer or a veteran of thousands of starlit nights, binoculars can be your best friend. Here’s how to get started.

A small section of the Milky Way photo showing Eta Carinae.  Image via Lehrstuhl für Astrophysik, RUB.

Milky Way photo with 46 billion pixels

It’s the largest astronomical image of all time, used by astronomers in the search for distant exoplanets and multiple star systems.

Shock waves streaming from a jet flying at supersonic speeds. The  jet is passing in front of the sun, and dark sunspots are also visible.   Image via NASA.

Seeing a jet’s shock wave

If you could see the shock wave from a jet moving faster than sound, this is what it would look like.

Image Credit: Aramgutang

What’s the birthstone for October?

October has two birthstones – opal and tourmaline.

View larger. | Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with color data from the Ralph instrument to create this enhanced color global view of Pluto. (The lower right edge of Pluto in this view currently lacks high-resolution color coverage.) The images, taken when the spacecraft was 280,000 miles (450,000 km) away, show features as small as 1.4 miles (2.2 km). Image via NASA/JHUAPL/SwRI.

First maps of Charon and Pluto

Many features on Charon informally named from science fiction, particularly Star Trek and Star Wars. Lord of the Rings, Stanley Kubrick also honored.