Going Loony

For years it drove me mad. I guess I should say "loony." But I'm starting to get used to it, resigned to the fact that some cartoonists just don't know their astronomy.  You've seen it: those crescent moons, whose "horns" are pointing the wrong way, like in the Mickey Mouse comic below.

 

Moon's wrong

Think about it.....the moon gets its glow from the Sun.  And if the Sun is lighting the Moon from the top, it would be up in the sky and it wouldn't be night! 

Now, I have to contend with these astronomical errors when trying to relax with a good book.  There I was, immersed in a historical novel about the 15th century English Plantagenets, when the author mentions the "waning moon rising off the horizon" at dusk. 

Waning Crescent Rising at Sunrise

Completely wrong. In that era of pitchblack nighttime skies, the Plantagenets themselves would be keenly aware how the Moon waxed and waned every four weeks—a waning Moon has its "horns" pointed up as it's rising in the East (as in the picture to the right).  That means it's being lighted up from the Sun just below it.  But, according to the novel, it's dusk, so the Sun has to be setting over on the other horizon in the west!  It can't be rising in the east at the same time.



Waxing Crescent Setting at Sunset

The author should have done their homework: a waning  crescent Moon rises just before dawn, not at sunset.  It is a waxing crescent Moon that is seen in the early evening. But it is not rising; it is setting in the west. 

How sad that in just a few short centuries, we've lost touch with the rhythms of the heavens.

Dark Matter Made Visible

I've been chasing the elusive dark matter story in astronomy for some twenty-seven years now, ever since I did an article on the "missing mass" in the (now defunct) Science Digest magazine in 1983.  I followed up with a book, Through a Universe Darkly, a decade later.  I haven't tired of the subject and still avidly follow each new clue that appears on the scene. It's mind-boggling that around 85 percent of the matter in the universe is in a form that remains invisible.

The latest evidence comes from the Hubble Space Telescope (HST).  A team of astronomers led by Dan Coe of NASA's Jet Propulsion Laboratory recently aimed a HST camera at a massive galaxy cluster known as Abell 1689, located more than two billion light-years away.  While astronomers can't see dark matter, they can certainly view its gravitational effects, especially in the way dark matter diverts light passing through the universe.  You might think of the dark matter in the cluster as a massive stone with the light passing by acting like a stream of water that comes upon the rock and is split into two or more streams.  In other words, dark matter bends light arriving from the distant galaxies behind it, much like a lens (which is why the effect is called "gravitational lensing"). What results is a funhouse view of the cluster, filled with myriad arcs, bands, and rings of light.  The amount of light bending provides the means to "weigh" the dark matter in the cluster.

This is not a new approach.  Abell 1689, due to its rich collection of galaxies, has been studied for years in this way.  But this latest image is the highest resolution yet, which enabled the astronomers to map the dark matter's distribution within the cluster. 

Galaxy Cluster Abell 1689, located 2.2 billion light-years distant

Each spot in this picture is a far-off galaxy, not a star.  The Abell 1689 cluster contains about 1,000 galaxies in all.  The light blue haze has been artificially added to indicate where the dark matter is concentrated within the cluster. 
Image Credit: NASA, ESA, and Z. Levay (STScI)

Capturing Primordial Starlight

Edwin Hubble at 100-Inch

 By 1936, Edwin Hubble was a dozen years into his search for distant galaxies. At that time, he could see out to several hundreds of millions of light-years, using the great 100-inch telescope atop California’s Mount Wilson. But even then the smudges on his photographic plates were dim, fuzzy, and next to impossible to identify.

“There,” wrote Hubble in his classic book The Realm of the Nebulae, “we measure shadows and…search among ghostly errors of measurement for landmarks that are scarcely substantial.”

Ever since, astronomers have struggled to trace the evolution of galaxies back through space-time—not just hundreds of millions of light-years but billions. For decades, all that astronomers could say with surety were that distant galaxies and clusters looked a bit “bluer,” a sign of heightened star formation as hoards of young, massive stars, flush with energy, put out more blue light.

Quasars, the brilliant cores of newborn galaxies, had long been sighted at great distances, but astronomers questioned whether they could truly understand the early universe by studying only its most active members.

But thanks to key technological breakthroughs over the last two decades—among them, the Hubble Space Telescope, the opening of giant telescopes in Hawaii and South America, and advances in telescopic detectors—more typical primordial galaxies are now being found, and at greater and greater distances.




UDFy-38135539 (circled in red) lurks within the Ultra Deep Field


The current record holder was recently discovered by a European team of astronomers using the European Southern Observatory’s Very Large Telescope (VLT) in Chile. It’s but a speck in the image, but a sensitive spectrograph allowed the observers to peg its distance. It’s more than 13 billion light-years from Earth and has been christened UDFy-38135539. That’s a mouthful for us but helpful to astronomers: the UDF stands for Ultra Deep Field (a region located in the southern-hemisphere constellation Fornax that was first closely imaged by the Hubble Telescope) and the number pegs its precise position on the sky.

The photons from this distant object started their journey when the universe was only 600 million years old. This was a time when a great fog of hydrogen gas, in which the universe was bathed, was just beginning to break up—cleared out by the fierce ultraviolet light emitted by newborn galaxies. The VLT likely sighted the new record holder through a break in the clouds, a lucky event for the astronomers and for us.  Through this fortuitous window, we get to see a bit of primordial starlight.

Picture Credits: (top) Huntington Library; (bottom) European Southern Observatory