The short video above clearly describes how the tilt of the Earth’s axis causes the seasons.
We’ve come to the end of February and tomorrow will tiptoe into March. Traveling at 66,487 miles per hour aboard spaceship Earth, you and I have traveled over 110 million miles around the sun since the first day of winter. That’s far enough to see a new set of constellations surge into the eastern sky as well as to change our hemisphere’s orientation with respect to the sun. No longer is the northern hemisphere pointed directly away from the sun as in December. Spring, the time of equality of light for both hemispheres, is just three weeks away. You’ve probably already noticed that the sun is considerably higher now at noon; it also rises and sets further north. We’ve gained a full hour of daylight in the morning and an hour and a half in the evening. Even with bright moonlight, I could still see the blue tint of twilight in the west yesterday at 7 o’clock.
The star Sirius sparkled in the southeastern sky when I photographed it at 7 p.m. in moonlight last night. Details: 35mm lens at f/2.8. 15-second exposure at ISO 800. Photo: Bob King
Speaking of twilight, two people asked me this week what that bright star is in the south just as the sky gets dark. Although we’ve visited with this star several times over the winter, it doesn’t hurt to return to it again in case you’ve forgotten. It’s Sirius in the constellation Canis Major and the brightest star in the entire night sky. No photo can quite capture its searing, magnesium-white flame. Sirius is 1.75 times the sun’s diameter and about 25 times brighter. Combined with its relative proximity to Earth of just 8.6 light years, it’s no wonder it shines so brightly. Sirius remains prominent in the southern sky throughout March.
Face the moon to find Saturn over the next couple evenings. Created with Stellarium
The moon will be full tonight and conveniently positioned midway between Leo the Lion’s brightest star Regulus and the planet Saturn. Tomorrow night it’s even closer to Saturn. If you’ve been wondering just how to find the ringed planet, let the moon be your guide.
Supernova (SN) 2010Y is an exploding star in the galaxy NGC 3392 not far from the bowl of the Big Dipper. The light from the stellar explosion is so intense it shines as brightly as the galaxy’s entire nucleus which is packed with millions of stars. NGC 3394 is another spiral galaxy in the same field of view. Credit: William Wiethoff
Champion supernova photographer William Wiethoff of Port Wing, Wisconsin sent me some photos of recent supernovas he photographed with his 14-inch telescope Friday night. At any particular time, there might be a dozen or so supernovas visible in galaxies beyond the Milky Way. Most are very faint and difficult to see visually but show up well in long time exposure photography. 2010Y was the 25th supernova discovered this year and was found by amateur supernova hunter Giancarlo Cortini of Italy on February 8. The host galaxy, NGC 3392 is located about 150 million light years from Earth. This one is bright enough to see at high power through larger amateur telescopes. Supernovas come in two basic varieties: supergiant stars that run out of nuclear fuel in their cores which leads to collapse, implosion and then explosion or white dwarf stars that "put on" too much weight and explode like titantic thermonuclear bombs.
Early this week spacecraft will make close flybys of three planetary moons. On March 2, Cassini will take closeup photos and "sniff" Saturn’s moon Rhea for unusual particles it might be giving off, while on the 3rd it will photograph the small moon Helene. Also the 3rd, the European Mars Express craft will take the closest pictures ever of Mars’ moon Phobos. We’ll have images to share as they arrive.