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what's up for july

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dark nebulae near the center of our

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milky way galaxy hello and welcome i'm

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jane houston jones at nasa's jet

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propulsion laboratory in pasadena

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california

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the milky way looks like a river of tiny

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diamond clusters surrounding mysterious

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dark islands

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notice how the milky way divides into

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two streams overhead

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between these two streams lies a dark

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band of starlight obscuring dust

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summer is the best time of year to

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observe these dusty areas

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the milky way thickens and brightens as

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it flows southward towards the horizon

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near the constellation sagittarius

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sagittarius is easy to see in the

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southern sky this month the brightest

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stars look just like a teapot and the

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center of our galaxy looks like hot

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steam spewing from the teapot spout

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dr e e barnard made the first wide-angle

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photographs of our milky way at lick

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observatory in 1889

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he saw dark regions visible among the

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mass of stars

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earlier astronomers thought these dark

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regions were simply areas where there

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weren't any stars

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barnard thought just the opposite he

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thought that these empty areas were

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actually concentrations of matter

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blocking our view

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he was correct

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a dark nebula called barnard 86 is one

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of his discoveries a dark nebula is a

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kind of interstellar cloud so dense that

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the light from background stars or from

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a mission and reflection nebulae is

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blocked

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like fog around a street lamp a

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reflection nebula shines only because

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the light from an embedded source

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illuminates its dust

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the nebula does not emit any visible

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light of its own

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emission nebulae are glowing clouds of

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interstellar gas which have been excited

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by some nearby energy source

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usually a very hot star causing them to

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emit light

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it takes radio or infrared astronomy to

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pierce these dark clouds and see beyond

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them

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the three dark lanes of dust in the

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trifid nebula can be seen in visible

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wavelength images

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infrared images from the spitzer space

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telescope reveal bright regions of

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star-forming activity

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there are many dark nebulae visible to

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the unaided eye

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look for the pipe nebula

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the lagoon nebula

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and the great dark rift above the teapot

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of sagittarius

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then when you look at the dust lanes

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within spiral galaxies you'll be able to

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compare them to the

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overhead in our summer milky way

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towards the end of the month don't miss

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the parade of planets low in the western

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sky

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mars and saturn march towards one

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another readying for their august first

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conjunction

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