When is the best time to see auroras? Where is the best place to go? And how do you photograph them? These questions and more are answered in a new book, Northern Lights - a Guide, by Pal Brekke & Fredrik Broms.
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CONTINUED QUIET: The sun's southern hemisphere is peppered with sunspots, but none of them is strongly flaring. Solar activity remains low. NOAA forecasters estimate a 15% chance of M-class solar flares and a scant 1% chance of X-flares on Dec. 6th. Solar flare alerts: text, voice
THE GHOST OF COMET ISON: This morning, Dec. 6th, leading researchers from the Comet ISON Observing Campaign (CIOC) held an informal workshop at the Johns Hopkins Applied Physics Lab. One of the key questions they discussed was, Did Comet ISON survive? It might seem surprising that anyone is still asking. After all, the "comet" that emerged from the sun's atmosphere on Thanksgiving day appeared to be little more than a fading cloud of dust. This movie from the STEREO-A spacecraft (processed by Alan Watson) shows the V-shaped cloud fading into invisibility on Dec. 1st:
The answer hinges on the contents of that cloud. Is it nothing more than a cloud of dust--or could there be some some fragments of the disintegrated nucleus still intact and potentially active?
A key result announced at the workshop comes from SOHO, the Solar and Heliospheric Observatory. According to the spacecraft's SWAN instrument, the comet stopped producing so-called Lyman alpha photons soon after its closest approach to the sun. Karl Battams of the CIOC explains what this means: "Without getting technical, Lyman-Alpha is a consequence of sunlight interacting with hydrogen, and if we are not seeing that interaction then it means that the levels of hydrogen (and hence ice) are extremely low. This is indicative of a completely burned out nucleus, or no nucleus at all."
"The evidence appears strong that at some point approaching perihelion - whether days or hours - Comet ISON likely began to completely fall apart," he continues. "What remains of ISON now is going to be either just a cloud of dust, or perhaps a few very depleted chunks of nucleus. Either way, it's not going to flare up at this point and we should assume the comet's show is over."
"However, we do need to verify this," says Battams. "Hopefully the Hubble team can come to the rescue! In mid-December, Hubble will be pointed in the direction of where ISON should be and they'll try and image something. If no fragments are surviving, or they are tiny, then Hubble will not be able to find anything, but that negative detection will tell us something: namely that ISON is indeed gone for good."
Comet ISON Photo Gallery
MAXIMUM VENUS: Lately, have you noticed an extremely luminous star in the southwest after sunset? That's no star. It's Venus, and tonight it is at its brightest for all of 2013. Only the Moon itself outshines the 2nd planet from the sun:
Alan Dyer took the picture from a spot near Rodeo, New Mexico, on Dec. 5th. "The clouds cleared just in time for us to catch a glimpse of the crescent Moon above Venus, now at its most brilliant for the year."
Venus registers -4.7 on the scale of astronomical magnitudes. That means it is almost 200 times brighter than a 1st-magnitude star. If you have binoculars or a small telescope, take a closer look. Like the Moon, Venus has phases and tonight it is 27% illuminated. The bright Venusian crescent is easy to see through backyard optics.
Realtime Space Weather Photo Gallery
WHO NEEDS COMET ISON? Astronomers are mourning the loss of Comet ISON, which disintegrated when it flew past the sun on Thanksgiving Day (Nov. 28). Who needs it? There is another comet brightening in the morning sky--naked-eye Comet Lovejoy (C/2013 R1). Martin McKenna sends this report from Northern Ireland: "This morning, the comet was easily visible as a fuzzy star of 4th magnitude with a long straight tail between the constellations Bootes and Hercules." He took this picture using a Canon 450D digital camera:
"I could see 5 degrees of tail with my unaided eye," continues McKenna. "Using the camera the tail was at least 10o long!"
Telescopes and longer exposures reveal much more. This image from Michael Jäger of Masenberg, Austria, shows a "disconnection event" disrupting the comet's tail on Dec. 5th. The disturbance could be caused by a gust of solar wind or perhaps an episode of vigorous outgassing in the comet's core.
Monitoring is encouraged. Comet Lovejoy is easy to find before dawn rising in the east before the sun. Sky maps: Dec. 6, 7, 8, 9.
Realtime Comet Photo Gallery
Realtime Aurora Photo Gallery
Every night, a network of NASA all-sky cameras
scans the skies above the United States for meteoritic fireballs. Automated software maintained by NASA's Meteoroid Environment Office calculates their orbits, velocity, penetration depth in Earth's atmosphere and many other characteristics. Daily results are presented here on Spaceweather.com.
On Dec. 5, 2013, the network reported 5 fireballs.
(3 sporadics, 1 sigma Hydrid, 1 Geminid)
In this diagram of the inner solar system, all of the fireball orbits intersect at a single point--Earth. The orbits are color-coded by velocity, from slow (red) to fast (blue). [Larger image] [movies]
Potentially Hazardous Asteroids (PHAs
) are space rocks larger than approximately 100m that can come closer to Earth than 0.05 AU. None of the known PHAs is on a collision course with our planet, although astronomers are finding new ones
all the time.
On December 6, 2013 there were 1443 potentially hazardous asteroids. Notes: LD means "Lunar Distance." 1 LD = 384,401 km, the distance between Earth and the Moon. 1 LD also equals 0.00256 AU. MAG is the visual magnitude of the asteroid on the date of closest approach.
| ||The official U.S. government space weather bureau |
| ||The first place to look for information about sundogs, pillars, rainbows and related phenomena. |
| ||Researchers call it a "Hubble for the sun." SDO is the most advanced solar observatory ever. |
| ||3D views of the sun from NASA's Solar and Terrestrial Relations Observatory |
| ||Realtime and archival images of the Sun from SOHO. |
| ||from the NOAA Space Environment Center |
| ||the underlying science of space weather |