NASA’s LADEE Probe Reaches Moon; Lunar Crescent And Venus Pair Up At Dusk

LADEE will explore the makeup of the moon’s flimsy atmosphere and test a cutting-edge communications system

NASA’s Lunar Atmosphere and Dust Environment Explorer spacecraft (LADEE) safely entered lunar orbit yesterday and will soon test its futuristic laser communications system. The Lunar Laser Communications Demonstration aboard LADEE will link up with ground stations in New Mexico, California and the Canary Islands, sending data packets back to Earth at the rate of hundreds of megabits per second.

A small sample of moon dust collected by the Apollo 17 astronauts looks like black powder. The vial is housed at the Laboratory for Atmospheric and Space Physics in Boulder, Col. Credit: Kevin Baird

After the testing is complete, NASA will lower LADEE’s orbit to begin its 100-day mission measuring the composition of the moon’s extremely tenuous atmosphere, where atoms are so few they never collide. LADEE will also explore the dust environment closer to the surface. Scientists hope to explain what causes the mysterious glow along the sunrise and sunset horizons seen by Apollo astronauts back in the 1960s and 70s. A leading theory holds that dust gets electrostatically levitated after being charged by solar radiation.

The crescent moon pairs up with Venus tonight and tomorrow at dusk. The map shows the sky about a half hour after sunset facing southwest. Created with Stellarium

As the spacecraft begins its mission, we can turn toward the crescent moon, now making its return to the evening sky at dusk. Tonight and tomorrow night it joins Venus – don’t miss the opportunity to see the two brightest nighttime sky objects together against a colorful twilight sky.

Crescent moon shortly before sunrise in the eastern sky on Oct. 2. The horns point up and to the right or west. Credit: Bob King

Every month we get two opposing crescents – one in the evening after sunset, with the crescent’s horns pointing to the left or east, and the other at dawn shaped like the letter “C” with horns pointed west. These two crescent regimes flank either side of the new moon phase, when the moon lies almost directly between the sun and Earth. Except during a solar eclipse, we can’t see a new moon because it’s nearly in the same line of sight as the sun and lost in the glare of day.

Dueling crescent moons are visible on either side of new moon phase when the moon passes between Earth and the sun in its orbit. Illustration: Bob King

A day or two before and after new, the moon lies far enough to one side of the Earth-sun line for its edge to turn into the sunlight. We see a shining crescent. As the moon continues along its orbit, the angle it makes to Earth and sun widens, and its phase waxes from crescent to half to full before returning to morning crescent and new.

With tonight’s crescent a brand new cycle begins. Watching the moon’s changing phases we become more familiar with its orbital motion and spatial relationship to the Earth and sun.

11 Responses

  1. Edward M. Boll

    I just bought the Fall magazine of Discover. It was all about Comet ISON. What I like about it is the every day assessment, telling how many minutes before sunrise ISON will rise before sunrise every day from Nov. 1- Dec. 31, which by that time will be circumpolar. Using my own magnitude figuring, I calculated that at present rate of brightening, ISON could be in the magnitude 2-3 range and brighter from Nov. 22- Dec. 5. Using the info of minutes before sunrise, I am happy to say that for those of us who know what we are doing the comet may be seen every day. But for the general public, the comet will be difficult to see over those 2 weeks. The magazine has a magnitude of -8.2 on Nov. 28. There is a possibility it could be much brigther than that at the immediate point of perihelion, although if it is I expect it to fade fast within 24 hours. Then it would be a daylight object if we shield it from the Sun.

    1. astrobob

      I think 2-3 mag. in late November is reasonable though a far cry from estimates made earlier in the year. Right at perihelion on Nov. 28 it could become very bright, but -8 might be pushing it. Again, it’s an open question since we’re dealing with comets, changeable and unpredictable beasts by nature. If it does reach -4 (Venus brightness) that would mean that immediately before and after perihelion it would shine around -1 to +1 — briefly. ISON will also be very close to the sun at that time, so great precaution will be needed for anyone attempting to see it. I observed ISON this morning under very dark skies – it’s presently around mag. 10.7.

  2. Edward M. Boll

    From Nov. 26 through Dec. 1, it is around .2 AU from the Sun or less. I am predicting that the very best that we can expect the comet to be on those outside dates would be around magnitude -1.

  3. Steve B.

    Hey, Bob!
    I got to watch the crescent moon and Venus pair drop slowly towards the horizon on my drive to Moose Lake this evening. At first I wasn’t sure, but then I realized that I could see a faint crescent of light on the OPPOSITE limb of the moon as well! I was wishing that I had my camera and tripod, and a chance to get a picture. Star/moongazing is tough to do while driving.

    1. astrobob

      Thanks Steve for writing in. I had to photograph a hockey game at 7 this evening but took 10 minutes first to enjoy and photograph the moon and Venus over the I-35 freeway. How scenic!

  4. Edward M. Boll

    With Venus, so low, Jupiter may be seem brighter. ISON may outshine Jupiter at perihelion but it won’t seem like it in the daylight.

  5. Giorgio Rizzarelli

    The use of the word “crescent” you make in English is curious for us Italians. The Italian word “crescente” as well as the Latin original “crescens” is the present participle of the verb “crescere” (Latin and Italian) meaning “growing”. So we apply this term only to the *waxing* Moon.

    For the waning Moon we use “calante”, meaning “decreasing”, and indeed sometimes we also use “decrescente”, like in a proverb… You mentioned the “C” shape. Well, an Italian proverb-memo says the Moon is liar, because it’s Decrescente (decreasing, waning) when drawing a C, and Crescente (waxing) when drawing a D.
    If it sounds confusing, luckily for us we have a better proverb-memo, much more popular, based on rhymes: “Gobba a ponente Luna crescente, Gobba a levante Luna calante”, with literal translation (except for rhymes) “Hump toward West (or at sunset) waxing Moon, Hump toward East (or at sunrise) waning Moon”.
    The fact that people watches sky more often in the evening than in early morning, and so sees more often the evening (waxing) moon which we call Crescente, is probably the reason why English adopted the word Crescent and not the one for waning.

    Our use of the word “crescente” also means we *don’t* use it for the crescent-shape phases (illumination <50%). Interestingly, although we in Italian have a scientific term for the gibbous phases ("gibbosa"), we don't have one for the (less observed) crescent-shape phases. However in colloquial language we call the crescent-shape (also as a general shape, not only for the Moon) "falce" or "falcetta" meaning sickle, or small sickle, or "mezzaluna" which means "half-moon", even when it is <50%. We Italian eat Croissants and sometimes use that French word, but most Italians ignore its connection with the word "crescent".

      1. Giorgio Rizzarelli

        Well, I though it was interesting for you also because the origin of the word – how it passed from meaning “waxing” in Latin, to today’s English usage.

        1. Sean

          many English speakers who have at one point played an instrument or otherwise studied music in a more formal manner, and no doubt some other members of the public, are quite familiar with the musical terms crescendo and decrescendo, since music is one area where Italian words have made it into English relatively unchanged. b4 reading ur post tho, Giorgio, i had never thought about their relation to the words crescent or croissant. grazie for the insight!

      2. Giorgio Rizzarelli

        And let me correct myself, when I wrote we don’t use the word “crescente” for crescent-shape, I mean we don’t use it specifically for that shape. Crescente for us (and the original Latin Crescens) simply means waxing (with any % of illumination).

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