|
|
Dark Sun Sizzling
| Title |
Dark Sun Sizzling |
| Explanation |
Is this our Sun? Yes. Even on a normal day, our Sun is sizzling [ http://antwrp.gsfc.nasa.gov/apod/ap970106.html ] ball [ http://antwrp.gsfc.nasa.gov/apod/ap970107.html ] of seething [ http://antwrp.gsfc.nasa.gov/apod/ap970108.html ] hot gas [ http://antwrp.gsfc.nasa.gov/apod/ap030729.html ]. Unpredictably, regions of strong and tangled magnetic fields [ http://www-spof.gsfc.nasa.gov/Education/whmfield.html ] arise, causing sunspots [ http://antwrp.gsfc.nasa.gov/apod/ap051106.html ] and bright active regions [ http://antwrp.gsfc.nasa.gov/apod/ap040726.html ]. The Sun's surface bubbles [ http://en.wikipedia.org/wiki/Granule_%28solar_physics%29 ] as hot hydrogen [ http://en.wikipedia.org/wiki/Hydrogen ] gas streams along looping magnetic fields. These active regions channel gas along magnetic loops [ http://antwrp.gsfc.nasa.gov/apod/ap050814.html ], usually falling back but sometimes escaping into the solar corona [ http://antwrp.gsfc.nasa.gov/apod/ap010408.html ] or out into space as the solar wind [ http://science.nasa.gov/ssl/pad/solar/sun_wind.htm ]. Pictured above is our Sun in three colors of ultraviolet [ http://imagers.gsfc.nasa.gov/ems/uv.html ] light. Since only active regions emit significant amounts of energetic ultraviolet light, most of the Sun appears dark. The colorful portions glow spectacularly, pinpointing the Sun's hottest and most violent regions [ http://antwrp.gsfc.nasa.gov/apod/ap060502.html ]. Although the Sun is constantly changing, the rate of visible [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html ] light it emits has been relatively stable [ http://en.wikipedia.org/wiki/Solar_constant ] over the past five billion years, allowing life to emerge [ http://www.pbs.org/wgbh/nova/origins/life-nf.html ] on Earth. |
|
Circum-axial Leaf Trails
| Title |
Circum-axial Leaf Trails |
| Explanation |
Are photographs of star trails [ http://www.astropix.com/HTML/I_ASTROP/TRIPOD/ TRIPOD2.HTM ] really evidence of the Earth's rotation [ http://www.astro.uiuc.edu/~kaler/celsph.html ] about its axis? Yes they are, and science journalist Trudy E. Bell discovered that there is a simple way to demonstrate this, if you have the stomach for it. First, find a playground equipped with a standard Merry-Go-Round [ http://scitation.aip.org/journals/doc/ PHTEAH-ft/vol_45/iss_2/85_1.html ] (MGR) located under or near a large, leafy tree. Seat yourself near the middle of the MGR platform. Ask a local playground expert (KID) to get you spinning very, very fast. As the scenery flashes by at a dizzying rate, point your camera skyward and take a picture with a slow shutter speed setting. The result will be similar to this excellent image of concentric, arcing leaf trails centered at a point corresponding to the MGR's axis of rotation - a convincing imitation of circumpolar star trails [ http://antwrp.gsfc.nasa.gov/apod/ap061202.html ] recorded in hours-long exposures [ http://antwrp.gsfc.nasa.gov/apod/ap060915.html ] of planet Earth's night sky. Then, just stand up and walk away ... if you still can [ http://youtube.com/watch?v=bWKUjKQxg0A ]. |
|
Diamond Ring in the Sun
| Title |
Diamond Ring in the Sun |
| Explanation |
Today, earthbound skygazers can celebrate a solstice [ http://www-spof.gsfc.nasa.gov/stargaze/Sseason.htm ], a new Moon [ http://aa.usno.navy.mil/faq/docs/moon_phases.html ], the closest approach [ http://mars.jpl.nasa.gov/ ] of planet Mars since 1988 ... oh yes, and a total eclipse of the Sun, the first total solar eclipse [ http://sunearth.gsfc.nasa.gov/eclipse/TSE2001/TSE2001.html ] of the third millennium. Of course for some, today's most spectacular celestial views will be of the eclipsed Sun [ http://science.nasa.gov/headlines/y2001/ast19jun_1.htm ] from along the path of totality as the new Moon's shadow tracks across southern Africa and Madagascar [ http://www.madagascar-eclipse2001.com/eclipse_.htm ]. This picture from the August 1999 total solar eclipse captures the shimmering solar corona just as that eclipse's total phase ended, as seen from eastern Turkey. The first rays of bright sunlight shinning through edge-on [ http://sunearth.gsfc.nasa.gov/eclipse/TSE2001/TSE2001fig/ TSE2001fig08.GIF ] lunar mountains and valleys create the fleeting appearance of glistening diamonds set in a ring around the Moon's silhouette. Do you want to see today's solar eclipse? Eclipse expeditions are offering live webcasts [ http://www.bit-net.com/~pauer/eclipse01/ ]. |
|
The Heart in NGC 346
| Title |
The Heart in NGC 346 |
| Explanation |
Yes, it's Valentine's Day [ http://antwrp.gsfc.nasa.gov/apod/ap020214.html ] (!) and looking toward star cluster NGC 346 [ http://www.seds.org/~spider/ngc/ngc.cgi?346 ] in our neighboring galaxy the Small Magellanic Cloud [ http://www.seds.org/messier/xtra/ngc/smc.html ], astronomers have noted this heart-shaped cloud [ http://chandra.harvard.edu/photo/2003/ngc346/ index.html ] of hot, x-ray emitting gas in the cluster's central region. The false-color Chandra Observatory x-ray image also shows [ http://xxx.lanl.gov/abs/astro-ph/0212197 ] a strong x-ray source just above the heart-shaped cloud which corresponds to HD 5980, a remarkable, massive binary star system that lies within the cluster. HD 5980 [ http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/stars/ hd5980_chandra.html ] has been known to undergo dramatic brightness variations, in 1994 briefly outshining all other stars in the Small Magellanic Cloud, and has been likened to the luminous, eruptive variable star Eta Carinae [ http://antwrp.gsfc.nasa.gov/apod/ap021010.html ] in our own Milky Way galaxy. At about 100 light-years across, NGC 346's [ http://www.asnsw.com/observing/clouds/tsmc5.htm ] heart-shaped cloud is probably the result of an ancient supernova explosion. Alternatively it may have been produced during past eruptions from the HD 5980 system, analogous to the nebula associated with Eta Carinae [ http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/ eta_car.html ]. |
|
|
