Astro Bob

  A thin layer of cells at the base of each leaf stem literally cuts the leaf off from the tree. Gravity assists in the process.  Bob King I've spent a lot of time in the forest lately watching leaves fall. When the wind blows they spiral, seesaw, twirl and drop to the ground. Leaves also fall when there's no wind. On an utterly still day this September I listened to the scratch and clatter as one leaf here and one leaf there broke free and tumbled earthward, guided by gravity. We know that leaves change color because the chlorophyll that drives photosynthesis breaks down and exposes other pigments that have been there all along. But why exactly do leaves fall? It turns out that trees simply get rid of them. They're baggage that might otherwise drain resources from the plant when the weather turns cold.  In response to a decrease in sunlight a tree makes special abscission cells that form along the juncture of the leaf stem and branch and slowly push the leaf away, cell ...

These photos depict the two hemispheres of Mars with a few of the most prominent features labeled. Olympus Mons is the largest and tallest volcano in the solar system with a height of 16 miles (25 km) and diameter of 374 miles (624 km). The hazy, white patches are clouds. North is up. Left: Damian Peach (Oct. 12). Right: Anthony Wesley (Oct. 4) Today, Oct. 13 is a special day for Mars. It's at opposition to the Earth and very close to us. If you go out tonight and look off to the southeast after 9 o'clock you can't miss it. Mars is so brilliant that sometimes I find myself just staring at it, amazed. We won't see it as good until 2035. Heck, I'll be 82 then. I'm not going to waste a mesmerizing minute. On Oct. 11, Mike Sangster of Duluth, Minn. used an 8-inch telescope to capture this photo of Mars and its two moons, Deimos and Phobos. Mars is so incredibly bright compared to the moons this was not an easy photo to take.  Michael Sangster At opposition, the Eart...

Venus, the lunar crescent and Regulus join forces at dawn tomorrow morning (Oct. 13) in the eastern sky. Stellarium I love October. The sun rises late which means you can get up early. For many of us sunup occurs between 7 and 7:30, making it easier to see pretty happenings in the dawn sky. For instance, tomorrow morning (Oct. 13) the waning crescent moon will join 1st magnitude Regulus, Leo's brightest star, and brilliant Venus in the east to make an attractive sight.   If you're up around 6 a.m. you'll see the trio in the growing light and may find it's just what you need to start the day. The moon is three days from new and will look like a bright rind edging the bottom of the darker, earth-lit disk. Direct sunlight illuminates the crescent; light reflected from the Earth dimly brightens the remainder.    Venus is a tiny gibbous "moon" in a telescope this month. Stellarium     As ever, Venus has a magnetic draw on the eyes, while dimmer Regulus completes...

  Mars can help us find the variable star Mira in the constellation Cetus the sea monster. The two are currently just a fist and a half apart. Mira is a pulsating variable star that physically expands and contracts, brightening and fading over a period of 332 days. Bob King The Red Planet squares off with a red giant this month. Mars is currently just 15° (a fist and a half) above and to the left of the one of the best-known variable stars, Mira the Wonderful. Mira gives cause for wonder because it occasionally glows as bright as the North Star and but then disappears from naked-eye view a few months later.  Mira animation. Merikanto / Wikimedia Commons. CC BY-SA 4.0 Mira's light varies because it pulsates. and changes in size which affects its temperature and brightness. Picture blowing up a balloon, letting out some of the air and then blowing it back up again. When Mira contracts it heats up and brightens, and when it expands it cools and fades.  You need a small tel...

Astro Bob entries on the Duluth News Tribune website today (Oct. 9). Before I share sky events I wanted to update you about the Astro Bob blog. I started writing it Feb. 2008 when I was a photographer and photo editor at the Duluth News Tribune. It became part of my daily work and contribution to the website. When I retired in 2018 I continued writing the blog as a freelancer for the newspaper, for which I'm grateful. Recently, the blog was transferred to a new weblink  where you can read the current entry and the full archive back to 2008. But there's a caveat. Not long ago, the newspaper website changed from free access to a paid subscription. Those of you who've tried to read the blog recently may have run into the "paywall."  With a digital subscription you can read Astro Bob anytime you want. Without one, access is limited to three visits a month. For the time being you'll still be able to read the blog on Blogger, Facebook and Twitter for free, but that...

A poplar tree in full fall regalia frames the waning gibbous moon this morning. Bob King I've written about seeing the moon in the daytime sky before. I hope you don't mind if I take another swing at the topic. Did you see the moon this morning? Just amazing. It caught my eye around 8 a.m. high in the southwestern sky couched in deep blue and framed by autumnal colors. Portrait of the full moon if the sun's light were suddenly extinguished. Can you find it? Stellarium with additions by the author For the next two hours as I went about errands it hung in clear view opposite the sun, illuminated by the light kindled by fusing atoms in its core. At a glance you could see one of the most important differences between a planet (or moon) and a star. A star makes its own energy and beams it across space in all directions. Moons and planets reflect a small portion of that light back, which renders them visible. Otherwise they'd appear as black silhouettes against the stars.  Th...

Mars leaves a bright glitter path on Lake Superior near Duluth, Minn. on a recent night. Bob King All eyes are on Mars this week. On Oct. 6 it will reach it's minimum distance from Earth of 38.6 million miles (62.1 million km) and shine incredibly bright, besting even mighty Jupiter. The two planets won't be this close again nor will Mars be as brilliant until September 2035. A week later on Oct. 13 Earth and Mars will be at opposition, precisely lined up together on the same side of the sun and only slightly less close. When the faster Earth laps Mars every couple years, the two planets come closest and Mars is said to be  at opposition . It lies directly opposite the sun in the sky — rising at sunset and setting at sunrise — and remains visible all night. Due to Mars's more strongly elliptical orbit (see below) some oppositions, like the current one, are closer than others. The closest are called perihelic while distant ones are aphelic. NASA Earth is the faster orbiting ...