Saturn disappears, Mercury appears during ‘night of the planets’


Saturn covered and uncovered by the moon earlier today by Dave Herald, Murrumbateman, Australia

Enjoy the video. Dave Herald did a great job recording this morning’s Saturn occultation. The images are very sharp. I always find it remarkable how atmosphere-less the moon is. There’s not a hint of softness in the planet as it’s devoured by the lunar limb. If there were substantial air, the planet would gradually soften and fade.

For a moon or planet to be completely without air is next to impossible. The solar wind knocks atoms from minerals on the lunar surface and sends them reeling into the virtual vacuum above the surface. Studies have found potassium, sodium, helium and argon in the moon’s exosphere, the name given to the lunar atmosphere. Bombardment of the moon’s surface rocks by micrometeorites and the solar wind release potassium and sodium; helium and argon probably bubble up from radioactive decay of those same rocks. Helium may also arrive via the sun’s wind.

Glow from sodium in the lunar atmosphere. The light from the moon has been blocked by the telescope, but the size, position and phase of the Moon are shown by the superimposed image in the center. Rayleighs are a measure of brightness. Credit: NASA

At sea level on Earth, we breathe in an atmosphere where each cubic centimeter contains 10,000,000,000,000,000,000 (10 quintillion) molecules; by comparison, the lunar atmosphere has less than a million molecules in the same volume.

Comets and meteoroids striking the surface temporarily enhance the amounts of other atoms and molecules. But the sum total of all the sputtering and interacting is an atmosphere equal to the amount of air you’ll find 250 miles high where the space station plies it orbit. Not much.

Mercury stands all by itself low in the northwest in this photo taken about 50 minutes after sunset last night. Credit: Bob King

At my house, we saw no occultation of Saturn, but the two did stand together in the southeastern sky at dusk. On the opposite end of the heavens, Mercury made a fine naked eye appearance in the northwestern sky.

Jupiter glows over Amity Creek last night. Both the creek and the sky were lit by the light of the full moon. Credit: Bob King

I first caught it around 9:15 p.m. some 40 minutes after sunset and watched it for at least a half hour. Capella and Jupiter – both higher up in a darker sky – made for great sight lines to the planet.See yesterday’s map for details.

Jupiter in Gemini remains the most brilliant object in the western sky at dusk during early evening hours. I watched it from a nearby creek that rushed with water from snow melt and recent rains.

Mars stood between Jupiter and Saturn. This week the ‘boring’ hemisphere – the one with fewest dark markings – is turned toward western hemisphere observers.

The Moon, Mars (upper right), Saturn (lower left), Spica (immediate right of moon) and Arcturus (top) as seen from Dayton, Ohio on May 12. Credit: John Chumack
Dayton, Ohio

But there’s still much to see – enough to easily stay up past your bedtime. The north polar cap on Mars remains visible despite the seasonal summer ‘heat’, and white clouds topping the planet’s major volcanoes are visible along the planet’s western edge. Check it out.

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

9 thoughts on “Saturn disappears, Mercury appears during ‘night of the planets’

  1. I can get pics of the 4 prominent moons of Jupiter with the 300mm lens on my camera, making up for my lack of magnification with a little exposure time. Can the same be done with Mars and Saturn? Or, are they just not bright enough?

    • Hi Guy,
      Mars will be impossible – they’re much too faint and too close to the planet. With Saturn, you might be able to get Titan (mag. ~8.5 or 2.5 mags. fainter than Jupiter’s moons) when it’s at greatest elongation from the planet. Greatest elongations occur about every 8 days. Another of Saturn’s moons, Iapetus, gets as bright as 10th magnitude at greatest western elongation only (occurs every 79 days – this month is not good). That’s a tougher one but might be possible with your setup.

      • That’s right Bob. I got too Titan at 300mm.

        And you’re right about Iapetus: at W max elongation it’s 10th magnitude, while at E max elongation only 12th and much more difficult to see, even in telescope.
        Already Cassini realized this difference and correctly guessed it was due to the two very different hemispheres of the moon, one icy, one dark. It’s interesting that, even when resolving a moon at one pixel, we can “see” such surfaces features.
        Here are two photos I got in telescope two years ago (the detailed Iapetus face photos are of course NASA pics) showing the big difference: at E (left) elongation it’s barely visible (also because postimage service lowered quality).
        http://postimg.org/image/khxa1zuuz/

        Yes this month is not good… The next Iapetus W elongation will be at beginning of Juli: Saturn at night will be rather low on horizon, due to summer’s long twilight, and Saturn being past opposition.

        Rhea is brighter than Iapetus but much closer to Saturn: at 300mm it’s probably covered by Saturn’s glare.

        Good luck Guy whatever moons you get!

        • Giorgio,
          Wow, that’s great you picked up Mimas in your telescopic photo of Saturn. I’ve tried for years to see Mimas but no luck. I regularly see Enceladus and have found Hyperion as well. The toughest solar system moons I’ve ever seen are Phobos and Deimos (used a C-11 and occulting bar) and Jupiter’s Himalia.

          • Yes a Star Wars fan cannot miss the Death Star. Ha, but this is in photo. And I hope it wasn’t camera noise – even in the original (not postimage degraded) I couldn’t exclude at 100% it wasn’t noise. These were single shots at mid ISO. Probably trying again these days, that I can use movie/stacking method, I could get rid of the noise.

            Respect about Phobos and Deimos! I was very impressed of the photos of them posted a few weeks ago by an amateur on spaceweather, and I couldn’t imagine you could get them in visual. Could you post some detail about the occulting bar (external obstacle or black tape in eyepiece – measures?)

          • Giorgio,
            I cut a little slice of aluminum foil and tape it across the middle of field stop of an older Orthoscopic eyepiece. When looking through the eyepiece, one sees a sharply defined opaque bar. Next I position Mars behind the bar in the correct orientation so the planet is completely hidden. This allows me to study the immediate area either side of Mars to find the moons. Deimos was rather difficult, but not nearly as hard as Phobos, which is closer in to the planet. I’ve seen Deimos a few times, Phobos just once. All the observations were made with Mars at perihelic oppositions. Neither moon is visible through my equipment during aphelic oppositions like the one we’re having now.

          • Thank you very much Bob. I must try this technique. It may be useful for other subjects too, like other planets and some difficult double stars.

          • Giorgio,
            Yes, it really works well for the moons of Uranus as well as Neptune’s Triton. Some modern eyepieces don’t have a field stop area that allows you to place an occulting bar at the sharp focus position, that’s why I use the older Ortho. I can also put it in a Barlow for more magnification.

  2. Small typo here too, do you mean Mars *North* polar cap? PS great pic the one of Jupiter at moonlight with river

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