Astro Bob A look at celestial happenings in the Northland and beyond Bob King View my profile Click here to view previous posts or additional resources

Making a cup of tea on the moon

Don't forget to watch for the International Space Station tonight. For those of us living in northern Minnesota / NW Wisconsin it will first appear in the southwest at 6:42 p.m. and cross directly in front of Orion's Belt as it moves eastward over the next five minutes. This will be one of its brighter passes in the coming week with an estimated magnitude of -3.0 -- nearly the equal of the planet Venus. Tomorrow I'll update the blog with a full week's worth of times and where to look.

The moon pays a visit to Antares in the scorpion tomorrow morning. Antares is a red supergiant star about 800 times larger than the sun or some 688 million miles in diameter. If you put Antares in the center of the solar system, we'd be orbiting inside the star and get fried to a crisp. Created with Stellarium

Planning on being up tomorrow morning between say 5 and 6? If so, direct your eyes to the moon in the southern sky. It will be in last quarter phase just to the left of the bright, red-hued star Antares in Scorpius the Scorpion. The terminator -- the border line between day and night on the moon -- has been slowly advancing to the left (eastward) since full phase. Tomorrow it will divide the moon exactly in half with one hemisphere in darkness and the other in sunlight.

Since we're both the same distance from the sun, the Earth and moon receive the same amount of light and energy so why is our planet so much friendlier to life? The answer is swirling around in your lungs at this very moment -- Earth has an atmosphere and the moon doesn't. Sunlight warms the ground and the heat that rises gets trapped by the air above. This warms our planet enough to allow water, essential for life, to exist as a liquid.  Oceans also play a major role in retaining and distributing solar energy. With no warm, fuzzy blanket of air for protection, the moon shoots from one extreme to the other. Under perpetually cloudless skies, daytime highs on the moon's surface rise to 225 degrees Fahrenheit while typical nighttime lows drop to 300 below.

The last quarter moon is resplendent with craters and mountain ranges that show beautifully in even a small telescope. The dark oval at top is the crater Grimaldi. Credit: Jim Misti

Earth rotates once on its axis in 24 hours giving us an average of 12 hours of daylight followed by 12 hours of night. The moon takes 27.3 days to complete one rotation so any particular spot on its surface is bathed in sunlight for 13 1/2 days followed by 13 1/2 days of night. No surprise then that it gets so hot. I happen to like tea a lot, especially the dark, malty Indian Assam varieties. You could boil water for tea at noon on the moon in seconds provided it was in a pressurized container. Just putting out a cup filled with water wouldn't work because with no atmospheric pressure, the water would quickly boil right out of the cup into the lunar vacuum.

At the other extreme, consider that the temperature of dry ice (frozen carbon dioxide) is 109 below. That seems mighty cold but 300 below is nearly the temperature of liquid nitrogen (-320 F). You might be familiar with liquid nitrogen -- doctors use it as a treatment for freezing and removing warts. 

One last thought about lunar temperatures and something to consider the next time you look at the moon. With no atmosphere, the transition between day and night would be very sudden. Temperatures would plummet hundreds of degrees in a very short time until hitting bottom during the long lunar night. 

The zodiacal light was visible this past Wednesday night. The cone or wedge-shaped glow is subtle and extends from the treetops at lower right up toward the Pleiades, the clump of stars at top left. Details: 20mm lens at f/2.8, ISO 1600 and 30" time exposure. Photo: Bob King

If you've never seen the zodiacal light, now is the best time to spot it in the western sky beginning around the end of twilight. The large, diffuse glow is sunlit comet dust in the plane of the solar system. It's centered on the zodiac -- the sun's path in the sky -- and visible for about an hour after twilight ends from a dark sky site. Try to get well away from the city to see this faint apparition. Presently the top of the glow touches the Pleiades or Seven Sisters star cluster. We see it best on dark, moonless March evenings because the sun's path is at a steep angle to the horizon this time of year. That places the zodiacal light relatively high up in the sky away from the lower atmospheric haze. Since it's dim, try sweeping your eye back and forth across the western sky to see it in better contrast to the dark sky around it.

Posted by: rking@duluthnews.com on 3/6/2010 at 9:13 AM | Comments (0) | Permalink | Edit

Tags: daily updates, space station, zodiacal light, astro bob, life, moon, antares, scorpius, temperature