Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2018 August 13
The Pencil Nebula in Red and Blue
Image Credit & Copyright: José Joaquín PerezExplanation: This shock wave plows through interstellar space at over 500,000 kilometers per hour. Near the top and moving up in this sharply detailed color composite, thin, bright, braided filaments are actually long ripples in a cosmic sheet of glowing gas seen almost edge-on. Cataloged as NGC 2736, its elongated appearance suggests its popular name, the Pencil Nebula. The Pencil Nebula is about 5 light-years long and 800 light-years away, but represents only a small part of the Vela supernova remnant. The Vela remnant itself is around 100 light-years in diameter, the expanding debris cloud of a star that was seen to explode about 11,000 years ago. Initially, the shock wave was moving at millions of kilometers per hour but has slowed considerably, sweeping up surrounding interstellar material. In the featured narrow-band, wide field image, red and blue colors track the characteristic glow of ionized hydrogen and oxygen atoms, respectively.
Wondrous moon and Venus on August 13
Above: Last month’s moon and Venus – July 15, 2018 – teaming up to reflect off Harrie Lake in Labrador City, Newfoundland. Photo by Timothy Collins. View full image.
On August 13, 2018, look west after sunset to see the young moon and planet Venus, blazing in the evening twilight. Then keep watching in the weeks ahead, as the moon sweeps past all four bright planets now in the evening sky. The moon and Venus rank as the second- and third-brightest celestial bodies, respectively, after the sun. So they’ll pop out in the west shortly after the sun goes down.
Dazzled yet? Now look for something more subtle, the soft glow of earthshine illuminating the night side of the moon. See it on John Ashley’s photo, above? Yes, that is the night side of the moon, not Earth’s shadow on the moon. Earthshine is twice-reflected sunlight, which bounces off Earth to the moon, and then back. Earthshine on the night side of the moon is analogous to bright moonlight illuminating an earthly landscape around the time of full moon. Indeed, from the moon right now, the Earth appears in a brightly shining, just-past-full phase. Binoculars will accentuate your view of earthshine on the moon’s night side.
And don’t forget to keep watching beyond August 13. Although Venus reigns as the sky’s brightest planet, it’s hardly the only bright beacon to light up the August 2018 evening sky. Three other planets beam as soon as darkness falls. When should you look for the other planets? They are arrayed across the sky. You can see them throughout the evening.
What time should you look? On August 13, look soon as the sky begins to darken if you want to see the moon and Venus. From middle latitudes in North America on the 13th, the moon and Venus sit rather low in the west at dusk. They follow the sun beneath the horizon roughly 90 minutes after sundown. At mid-northern latitudes in Europe and Asia, the moon lurks low in the sky at dusk on August 13 and sets before Venus does.
From the Southern Hemisphere, the situation is different. The waxing moon and Venus appear higher up at dusk on August 13, and stay out well after nightfall. The reason is it’s nearly spring there now. Spring skies (from either hemisphere) bring an ecliptic – or path of the sun, moon and planets – that’s nearly perpendicular to the horizon. From temperate latitudes in the Southern Hemisphere (Chile, Argentina, South Africa, southern Australia, New Zealand), Venus is out for nearly 4 hours after the sun!
Click here for recommended sky almanacs; they can give you the setting times of the sun, moon, Venus and other planets in your sky.
Now about Mars. From anywhere worldwide, it’ll be hard to miss Mars. It’s the third-brightest heavenly object to adorn the August 2018 night sky, after the moon and Venus. Look in a southeast direction at dusk and nightfall to get an eyeful of this world that is way brighter than any true star. Above Mars you’ll find the golden planet Saturn. Although Saturn pales when contrasting it with the red planet Mars, this golden world nonetheless shines as brilliantly as a 1st-magnitude star.
Bottom line: Yes, you can see four bright planets as soon as darkness falls in August 2018. This evening – August 13, 2018 – the great celestial drama begins when the moon and Venus first pop out into the western sky at dusk.
Bruce McClure has served as lead writer for EarthSky’s popular Tonight pages since 2004. He’s a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.
Published on EarthSky
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