Skywatching Guide Archive
    April 22, 2016
  • The moon. It casts its cool glow over romantic strolls, inspires poetry, catches the eye (sometimes in broad daylight) and sends some astronomers fleeing indoors until the satellite once again departs the night sky.

    In this edition of Mobile Astronomy, we'll explore Earth's nearest natural satellite with apps that show where it is and what phase it's in (now, and in the future); apps with maps labeling the lowlands, mountains and craters; apps highlighting exploration missions; and even some free digital books about the moon that you can have with you at the eyepiece or just relaxing at the cottage this summer.

    The Earth and moon dance

    The moon, also known as Luna, is Earth's nearest celestial neighbor. At a mean distance of approximately 240,250 miles (384,400 kilometers), the light from the moon (which is reflected sunlight) takes 2.3 seconds to reach the Earth. The moon completes one orbit of the Earth every 27.3 days. Due to mutual gravitational tidal forces between the Earth and moon acting over millions of years, the moon's rotation has been slowed until it equals the satellite's orbital period. This is why Earthlings always see the same face of the moon.

    The SkySafari 5 app for Android and iOS lets you demonstrate that the moon is rotating by viewing the Earth-moon system from an outside vantage point. Open the app, search for the sun and tap the Orbit icon. The app will show the entire solar system from afar, in 3D, complete with planet orbits. At this point, you can move the model around, zoom in and out, and run time forward or backward to see the planets' motions. While still in this mode, search for the moon, tap the Center icon and then use two fingers to enlarge the moon until it becomes a globe. Use Center again whenever the moon drifts out of view. Bring up the time controls and select Day as the interval. Now, stepping or flowing time shows the moon rotating as it orbits the Earth.

    April 22, 2016
  • The smallest full moon of 2016 will light up the night sky this weekend, and you can get a sneak preview of the lunar event in a free webcast from the Slooh community observatory tonight (April 21). 

    The full moon of April, which is traditionally known as the Full Pink Moon or Pink Full Moon, actually occurs on Friday night (April 22). This year, April's full moon will be the smallest of the year because the moon will be at the farthest point from Earth in its elliptical orbit. Slooh representatives have dubbed the event a "mini-moon" and will showcase live views of the full moon on beginning at 8 p.m. EDT (0000 GMT) tonight. 

    "As the Earth and moon move to their furthest points from each other, we'll all get a unique chance to see the full moon as it appears smallest to us here on Earth … a 'mini' moon, and a Pink Full Moon at that," Slooh representatives said in a webcast announcement. You can also watch the April full moon webcast on here , courtesy of Slooh.

    During tonight's webcast, Slooh astronomer Bob Berman and host Paul Cox will be joined by Janice Stillman, editor of The Old Farmer's Almanac, to discuss the upcoming full moon, why it's known as a Pink Moon and why it is the smallest of its kind this year. Live images of the moon will be provided by Slooh's flagship observatory at the Institute of Astrophysics in the Canary Islands. 

    Viewers will be able to ask questions about the moon via Twitter by sending messages to @Slooh or by joining the webcast's live chat, Slooh representatives said.

    You can find tips on how to observe the moon in our infographic. If you need some photography tips, check out's photo guide for moon observers by veteran night sky photographers Imelda Joson and Edwin Aguirre.

    April 22, 2016
  • Once again, a skywatching hoax has gone viral.

    To go along with the infamous "Mars hoax," which claims that the Red Planet will appear as large as the full moon in the sky; the "Nibiru cataclysm," a supposed disastrous encounter between Earth and a large planetary object; and "Zero-Gravity Day," when people on Earth supposedly can experience weightlessness, we now have the "nights of the green moon."

    This latest fallacy to sweep the blogosphere claims that on Wednesday (April 20), and again on May 29, the moon will appear to turn a shade of green. The full moon of April will occur on Friday, April 22. [The Moon: 10 Surprising Lunar Facts ]

    The explanation given for the verdant metamorphosis is that several planets are going to align (wrong!), causing the moon to glow with an eerie, greenish light for about 90 minutes. This spectacle is exceedingly rare (so we are told), and last took place way back in the year 1596.
    As has been the case with the bogus Mars, Nibiru and zero-gravity hoaxes, the green-moon message implores you to "share this event!" And sadly, many people have apparently been snookered into doing just that.

    Interestingly, the date given for the first "moon of a different color," April 20, is also "National Weed Day" — a day that celebrates the smoking of marijuana and cannabis culture in general. Pot enthusiasts refer to the day numerically ("four twenty"), and the stated interval between "green moons" is said to be 420 years.

    The moon is gray. This fact will not change on April 20, 2016.
    The moon is gray. This fact will not change on April 20, 2016.
    Credit: NASA/GSFC/Arizona State University
    These may not be coincidences. It could very well be that whoever came up with the "green moon" story chose the April 20 date and/or the 420-year period as a reference to National Weed Day, whose predominant color is also green.

    The original green-moon deception indicated that Earth's nearest neighbor would change hue on May 29. The supposed explanation was that the moon would be just 4 degrees from the green-hued planet Uranus in the sky, and would somehow acquire a green sheen from the close interaction. This will not happen, of course.

    Somehow, that initial story was amended, and April 20 came into the picture as well. In any case, the nights of the "green moon" are nothing more than an urban legend. And if you're a faithful reader of, you already knew that these stories are hoaxes, because you've consulted our list of the top skywatching events of 2016. The green moon is not mentioned.

    May 04, 2016
  • For 7 1/2 hours, Mercury will be visible crossing the face of the sun. A telescope with proper solar protection and magnifying at least 60 times is needed to see Mercury’s tiny disk.
    For 7 1/2 hours, Mercury will be visible crossing the face of the sun. A telescope with proper solar protection and magnifying at least 60 times is needed to see Mercury’s tiny disk.
    For 7 1/2 hours, Mercury will be visible crossing the face of the sun. A telescope with proper solar protection and magnifying at least 60 times is needed to see Mercury’s tiny disk
    May 04, 2016
  •  Even from a big city, one can see the moon, a handful of bright stars and sometimes the brightest planets. But to fully enjoy the heavens — especially a meteor shower, the constellations, or to see the amazing swath across the sky that represents our view toward the center of the Milky Way Galaxy — rural areas are best for night sky viewing. If you’re stuck in a city or suburban area, a building can be used to block ambient light (or moonlight) to help reveal fainter objects. If you’re in the suburbs, simply turning off outdoor lights can help.