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 1
The Iris Nebula in a Field of Dust
Image Credit & Copyright: Franco Sgueglia & Francesco Sferlazza
Explanation: What blue flower grows in this field of dark interstellar dust? The Iris Nebula. The striking blue color of the Iris Nebula is created by light from the bright star SAO 19158 reflecting off of a dense patch of normally dark dust. Not only is the star itself mostly blue, but blue light from the star is preferentially reflected by the dust — the same affect that makes Earth’s sky blue. The brown tint of the pervasive dust comes partly from photoluminescence — dust converting ultraviolet radiation to red light. Cataloged as NGC 7023, the Iris Nebula is studied frequently because of the unusual prevalence there of Polycyclic Aromatic Hydrocarbons (PAHs), complex molecules that are also released on Earth during the incomplete combustion of wood fires. The bright blue portion of the Iris Nebula spans about six light years. The Iris Nebula, pictured here, lies about 1300 light years distant and can be found with a small telescope toward the constellation of Cepheus.
Orion the Hunter returns before dawn
Around early August, if you’re up early and have an unobstructed view to the east, be sure to look in that direction in the hour before dawn. You might find a familiar figure – a constellation that always returns to the sky around this time of year. It’s the beautiful constellation Orion the Hunter – recently behind the sun as seen from our earthly vantage point – now ascending once more in the east before sunrise.
The Hunter appears each northern winter as a mighty constellation arcing across the south during the evening hours. Many people see it then, and notice it, because the pattern of Orion’s stars is so distinctive.
But, at the crack of dawn in late summer, you can spot Orion in the east. Thus Orion has been called the ghost of the shimmering summer dawn.
The Hunter rises on his side, with his three Belt stars – Mintaka, Alnitak and Alnilam – pointing straight up.
Also, notice the star Aldebaran in the constellation Taurus the Bull. Aldebaran is the brightest star in Taurus the Bull. It’s said to be the Bull’s fiery red eye. See the V-shaped pattern of stars around Aldebaran? This pattern represents the Bull’s face. In skylore, Orion is said to be holding up a great shield … fending off the charging Bull. Can you imagine this by looking at the chart at top? It’s easy to imagine when you look at the real sky before dawn at this time of year.
Bottom line: The return of Orion and Taurus to your predawn sky happens around late July or early August every year. In the Northern Hemisphere, Orion is sometimes called the ghost of the summer dawn.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.
Originally published on EarthSky
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