Return Of The “Pink” Planet

This map shows the sky from mid-northern latitudes facing west about a half hour after sunset tonight Feb. 12, 2013. Mercury lies about “two fists” below the moon in bright twilight. Fainter Mars is a few degrees below Mercury. Created with Stellarium

Don’t look now, but there’s a new planet creeping up from the western horizon. Mercury makes a special guest appearance at dusk for the next week or so. Tonight the moon can help you find this elusive planet. What makes it a hard catch? Well, it never strays far from the sun, appropriate behavior given that Mercury is, after all, the innermost of the eight planets. Typically it stands just two fists held at arm’s length above the horizon after sundown. If trees or buildings get in the way, you won’t even notice it.

Tonight it shines brighter than Rigil in Orion and nearly matches Canopus, the second brightest star in the entire sky. But you’d never know it. Trapped near the horizon, the little planet must compete against the orange glow of dusk and the greater thickness of air there.

Mercury (top) and fainter Mars shine together at dusk as seen from the Gulf of Trieste along the Adriatic Sea on Feb. 10, 2013. The photo nicely captures their naked eye appearance. Credit: Giorgio Rizzarelli

As we know from personal experience, the sun’s light is more tolerable near sunrise and sunset. Likewise, the rising moon is considerably fainter than one seen overhead. Dust and air molecules absorb and scatter light, especially when we direct our gaze horizon-ward where the air, water vapor and dust are thickest. Astronomers call this phenomenon atmospheric extinction. It’s the reason they wait for stars to get high enough to clear the thickest air before gathering data.

By the time Mercury becomes visible a half hour to 45 minutes after sunset, air and dust have dimmed it by more than a magnitude, making it similar to Betelgeuse in brightness. If all this talk of extinction makes you pessimistic about seeing the planet, I apologize. Mercury’s not hard to spot if you’ve got haze-free skies and an unobstructed western horizon. Don’t be afraid to cheat a little with binoculars. I sometimes use them to find a twilight planet early so I know better where to look once the sky gets darker.

Mercury photographed by NASA’s MESSENGER spacecraft. The generally gray globe is mostly blanketed by volcanic rocks. Credit: NASA

If you want a real twilight challenge, try finding Mars below Mercury. It’s not only fainter but being lower, even more of its light is sucked up by the air. Binoculars are essential for this one.

As a kid I always thought Mercury was a red-hued world and saw it that way whenever it would make one of its twilight appearances. Truth is, the planet is quite gray, much like Earth’s moon. Photographs from the MESSENGER spacecraft show a surface covered in ancient volcanic rocks. Only later did I realize that my pink planet gathered it color from the very twilight itself. What color does it look to you?

18 Responses

  1. Lynn

    Great blog Bob, worth the wait and that is a stunning picture from Georgio, the photos you put on your blogs never ceases to amaze me, i’ve had quite a few favorite ones from you. Thanks

      1. Giorgio Rizzarelli

        Thanx Lynn, it’s really a poor quality (“noisy”) photo – it wan’t easy to catch in camera also Mars. As Bob said in the blog, due to atmospheric extinction at low altitudes in sky, Mars requested binoculars to be observed.
        Mercury instead, especially when it was enough darker, was quite well visible at naked eye. Due to its gibbous phase it had magnitude -1 almost like Sirius, the brightest star in sky, but the low atmosphere extincted it to 0 like Rigel (thanx Bob for underlining this), which is anyway still much!
        You find more details in my comment under the Mars-Mercury blog of Feb7.

    1. Giorgio Rizzarelli

      Thanx for the update. So in few weeks we here in N will have something more interesting to watch at dusk!

  2. James

    Bob, I live in west fargo, nd and my son and i were out @ 6:30 this evening. Looking south we saw a bright planet and and orange planet underneath. Off to the east a short distance was orion. These planets would have been mercury and mars right?
    Also at the timed we were watching the planets the space station raced across the sky with a satellite not far behind. Sky was amazingly clear. A crescent moon was in the west. Just beautiful.

    1. astrobob

      Hi James,
      Sounds like a great night. The bright planet you saw to the south was Jupiter. The orange “planet” underneath was actually the star Aldebaran. To find Mercury you needed to look well below the moon in the western sky around 6-6:30 p.m.

  3. H.Bob

    Excellent photo from Girorgo, I am not sure which I like better, the sky or the Adriatic. What a great place to live.

    It is a bit confusing, however, that Mercury, the smaller planet and further planet appears larger and closer than Mars? Even the fact that Mercury is above Mars seems odd. I suppose that is from thinking (erroneously?) that the planets of the solar system lie on a plane. I have to say that although I have an excellent “sense of direction” on terra firma, it seems to elude me when looking skyward.

    1. astrobob

      They planets do lie approximately in a plane, however that plane appears at various angles to the horizon depending on the direction you’re facing, your location and Earth’s axial tilt. If we could see Mars and Mercury when they’re due south at midday they would be nearly on a horizontal east-west line. By the time they’ve moved into the west, they “tip over” to the side.

      1. H.Bob

        Thanks AstroBob, that’s good to know, but will have to think about it more until I get a real sense of three dimensional space. I wonder if it is natural for the planets to be in a plane or why that happened? It seems that since the sun is spherical, they could also orbit in different planes like electrons in an atom.

        1. astrobob

          The planets lie in a plane because the spherical cloud from which the sun and planets formed flattened as it condensed towards its center (where the sun eventually formed) and sped up. It’s the same way a skater speeds up when she pulls in her arms.

          1. Giorgio Rizzarelli

            Yes, as the cloud shrinks for gravity, for the “skater effect” (which physicists call “angular momentum conservation”) it acquires rotation, and this for centrifugal force makes it flattening.

            Your point is interesting H.Bob, as various exosystems, though probably originating from a protoplanetary disk (we saw many of them), are not as such. In these systems the orbit planes of the planets have big inclinations one respect the other: the ecliptic, or plane of the system, which we take for granted, is not always present.

            Even for galaxies the rotation plane, though common, is often not defined.

    2. Giorgio Rizzarelli

      Thanx H.Bob. Mars is fainter because is now almost on the other side of the Sun. Mercury is instead near the Sun; really “lateral”, so appearing to us at “max elongation” angle from Sun. See the Solar System chart here:
      Also, in those days Mercury was particularly brilliant because of its gibbous phase.

      As for the Solar System plane, I quote A-Bob: we see the plane projected on the fixed-stars sphere, as a line called “ecliptic”. Most Solar System bodies (Sun, Moon, planets) stay approximately on this line. As the sphere rotates daily (the apparent effect due to Earth’s rotation), the ecliptic, “sticked” on it, also moves respect horizon.
      A good way to see this is installing the free software from Set your location, press the comma key to see ecliptic, watch at horizon at dusk, then change hour and season.

      A steep ecliptic is, together with max elongation along the ecliptic, a necessary condition to see Mercury at naked eye, because this results in Mercury being enough high on the horizon after sunset, to avoid losing it in the mist. As consequence we can see Mercury at naked eye only few weeks per year. In this season, we at mid N latitudes have currently a very steep ecliptic, which makes this the best week of the year to see Mercury.

      Additionally, the planets (and Moon) have really an inclination respect the average Solar System plane, so they usually don’t appear exactly on the ecliptic. In this case this summed to the steep angle effect, making the planets appearing one almost above the other.

      1. H.Bob

        Thanks for your detailed explanation Giorgio. That solar system chart makes a lot of sense, I don’t know why I did not consider that Mars could be at a further point because of its orbit. Maybe I will have to try Stellarium at some point to get an idea of how things move. I already use a couple of sky-watching apps on iPad which I find invaluable for learning the motion of the shy and identifying objects. I will have to try and catch Mercury this February if British skies ever re-present themselves! (It’s been cloudy.)

        1. Giorgio Rizzarelli

          Oh you’re British, so a fellow European. Love England.

          We amateurs know well that Mars is distant now, because it’s not interesting in scope. To see details of Mars you need the period when it’s at close approach (the opposition).

          You find Stellarium also for iphone & ipad (google it) and it’s very fast to install and use.

  4. Edward M. BOll

    Thanks to your info, I saw Mercury and Mars last night. I had not seen Mars in several months. I saw that Mars set at 7:04 and Mercury at 7:23. So, I went out at 6:45 and Mars was half of Mercury’s altitude. I could not have done it without 20 power binoculars.

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