Enjoying EarthSky? Subscribe.

221,461 subscribers and counting ...

Image via Tim Jones/McDonald Observatory.

Star of the week: Gamma Cephei

Gamma Cephei (aka Errai) is a binary star system with at least one planet. It’ll someday be a North Star for Earth.


Moon and Mercury on September 29

Mercury and the moon get close on the morning of September 29! They’re easiest to see from the Northern Hemisphere or southern tropics.


Moon and Mercury shortly before sunrise

September 28 is also the day of Mercury’s greatest elongation, when the planet will be 18 degrees west of the sun on our sky’s dome. Look shortly before sunup.


Moon and star Regulus before dawn

Everyone around the world can see the moon and Regulus these next 2 mornings. From the Northern Hemisphere, you might also see Mercury.


Use Cassiopeia to find Andromeda galaxy

Many use the constellation Cassiopedia – which is easy to find, shaped like an M or W – as a jumping off point for locating the Andromeda galaxy.

The moon was almost exactly at last quarter when Jenney Disimon in Sabah, North Borneo captured this photo on July 27, 2016 (5:30 a.m. local time, or July 26 at 21:30 UTC).

Last quarter moon is September 23

Fun time to see a last quarter moon: just after it rises, shortly after midnight. Then the lighted portion points downward, to the sun below your feet.

Skywatcher, by Predrag Agatonovic.

Late September-October planet guide

Use the moon to catch Mercury before dawn in late September, 2016. Then watch as Jupiter pairs with Mercury in the picturesque glow of dawn on October 11.


Moon, Castor and Pollux before dawn

Enjoy the moon and Gemini stars, Castor and Pollux, as the moon makes its monthly journey through the zodiacal constellation Gemini the Twins over the next few days.

Image Credit: Esparta

All you need to know: September equinox

2016’s September equinox arrives on the 22nd. Happy autumn (or spring)!

Where does the celestial equator intersect your horizon?  No matter what you latitude is, it intersects your horizon at points due east and due west.  Read more about how an observer's latitude affects your visible sky.

Equinox sun rises due east, sets due west

It’s often said that – at each equinox – the sun rises due east and sets due west. And that’s true. But why? How can you conceptualize this?


Astro festivals, star parties, workshops

Looking for something to do on the weekends? At star parties, amateur astronomers with telescopes will show you the night sky. Find one near you …

This image shows the debris ring around Fomalhaut and the location of its first known planet. This is the actual discovery image, published in the journal Science in November, 2008. Fomalhaut b was the first beyond our solar system visible to the eye in photographic images. Image via Hubble Space Telescope.

Fomalhaut had first visible exoplanet

Fomalhaut is sometimes called the Loneliest Star. Its planet, Fomalhaut b, was the first planet beyond our solar system to be visible to the human eye.

The day arc of the Sun, every hour, during the equinoxes as seen on the celestial dome, from the equator. Also showing 'twilight suns' down to -18° altitude. Note the Sun in the zenith at noon and that the tree's shadow is cast straight down, i.e. it stands in the center of its own shadow.  Image via Tau?olunga at Wikimedia Commons

Sun over Earth’s equator at equinox

At tomorrow’s equinox, the midday sun will be straight overhead seen from Earth’s equator. The sun will be crossing the sky’s equator, going north to south.


Where’s the moon? Waning gibbous

The Northern Hemisphere’s Harvest Moon has come and gone. The moon is now waning and rising later at night.

Relative to the backdrop stars of the zodiac, the moon moves an average 13o eastward per day. The green line depicts the ecliptic - the sun's annual path and the moon's approximate monthly path through the constellations.

Moon sweeps through Taurus the Bull

Use the waning moon to find Aldebaran, brightest star in Taurus, and the Pleiades star cluster. Plus info on the occultation of Aldebaran by the moon.

Sunrise over Red Sea by Graham Telford

Year’s fastest sunsets around equinoxes

The sun sinks below the horizon faster around the September and March equinoxes than at any other time.


How to find Fomalhaut, the loneliest star

Go outside around mid-evening – and learn to keep the loneliest star company.

Photo Credit: Dan Bush

Daytime moon, west after sunrise

Although we’re past full moon now, the moon is still big and bright. Also, watch each morning in the west for a pale daytime moon floating against a blue sky.

Moon Sept. 18, 2013 by Amy Simpson-Wynne

2016’s close and large Harvest Moon

This year’s Harvest Moon on September 16 happens to be an especially close and large full moon. Some will call it a supermoon. Notice that it’s very bright!


What’s special about a full moon?

The September 16 full moon is the Northern Hemisphere’s Harvest Moon. But all full moons are special. Here’s why.