The smallest and largest planets dance in the west tonight

By Phil Plait | March 14, 2011 7:00 am

If you have good eyes and a flat horizon, then you can spot Jupiter and Mercury this week as they pass each other in the night twilight.

As the planets orbit the Sun, we see their position in the sky change. Right now, Jupiter is (apparently) getting closer to the Sun every day, setting in the west a bit earlier every night. Mercury, on the other hand, is apparently moving away from the Sun, getting higher off the horizon with each passing day. On the evenings of March 14 and 15th the two planets will pass each other, with a closest approach of roughly 2° — about 4 times the width of the full Moon. That’s actually pretty close, and they’ll make a pretty pair in the west just after sunset.

And I do mean just. When the Sun sets, the two planets will be only about 10° off the horizon, where the sky will still be bright from twilight. Even though Jupiter will be shining at a magnitude of -2 (making it the fourth brightest natural object in the sky after the Sun, Moon, and Venus), and Mercury at -1, they might be a bit tough to see depending on your local conditions. Binoculars might help, but make sure the Sun is gone before scanning for the planets!

The image above is a rendering using software of what the scene might look like for you. This shows the view just after sunset, with the pair labeled. Funny, too: when I made this, I saw just how close the Sun was to setting due west. That means spring is almost here! The Sun sets due west on the equinox, which is March 20 this year.

Anyway, if you get the chance to see the two planets, take it! Jupiter will be a morning object after this, and won’t be visible unless you get up at the wee hours. Mercury moves rapidly day after day compared to other objects, and never gets very high off the horizon. Most people have never seen it, so you should grab this opportunity… after all, it’s not often the solar system’s most extreme planets flirt this way.

CATEGORIZED UNDER: Astronomy, Cool stuff
MORE ABOUT: Jupiter, Mercury

Comments (30)

  1. What’s the big W on the ground?

  2. Messier Tidy Upper

    But the smallest planet isn’t Mercury it’s Pluto, no, Makemake, no, Haumea no, *Sedna* isn’t it? ;-)

    After all, dwarf planets are still planets just as dwarf stars are still stars & those who say different can take a long walk off a short jetty far as I’m concerned! :-P

    Oh & does that mean they’ve discovered “Tyche”* which is supposed to be larger than Jupiter albeit *much fainter too?! ;-)

    * See :

    http://blogs.discovermagazine.com/badastronomy/2011/02/14/no-theres-no-proof-of-a-giant-planet-in-the-outer-solar-system/

    &

    http://en.wikipedia.org/wiki/Tyche_(hypothetical_planet) for more.

  3. rob

    first time I saw Mercury was last year when it was close to Venus. Gonna go look tonight if it is not cloudy! Thanks for the heads up Phil!

  4. I got to see Jupiter and Mercury Friday and Saturday nights as I found myself driving during the late twilight hours. I was on the road again Sunday night, but there were more clouds in the sky, and while I saw Jupiter, I missed Mercury.

    I should note that I saw Mercury while driving a Mercury!

  5. RwFlynn

    Oh boy. It’s gonna hurt not knowing where my old binoculars went. I know just the place to go search the skies from too!

  6. Gus Snarp

    Too hilly around here, not a chance of seeing this for me.

  7. Buxley

    @1: It’s either West or we’ve finally located ‘The Big W’ from “It’s A Mad Mad Mad Mad World”. =)

  8. kevbo

    Biggest planet? Isn’t that Tyche?

    :-/

  9. benj

    What software did you use to render the picture?

  10. Lupine

    I saw those two just last night and was wondering about them.

  11. jjgboulder

    Hey Phil, When you say due west, don’t you mean at the equator? Us folks in the frozen tundra, aka Boulder, would see it a bit more south, wouldn’t we?

    John

  12. Conshycrush

    Saw them sunday night out my back window looking west. Beautiful! First time i’ve ever seen Mercury! Even my girlfriend was in awe… then she was like “ok, i’m going back to watching One Tree Hill”… women!

  13. JohnK

    The MESSENGER Spacecraft enters Mercury orbit on 3/17, this Thursday.

  14. Hum,
    Clouded out here, but i’ll try tomorrow to see the allusive ‘big W’.

  15. Jeff

    #11

    I doubt that the latitude will matter because it is near the vernal equinox, when the sunsets due west everywhere

  16. Josie

    Hopefully it won’t be too froggy tonight over the ocean. While i get stunning sunsets from my balcony i often miss low horizon objects due to haze/fog/smog whatever low over the ocean.

    btw for anyone else who is sky object challenged such as myself I can recommend the SkyWalk app for the iPhone. It’s all of $3 and it’s a handheld planetarium. It’s a great set of trainnig wheels for folks who don’t have anyone to instruct them on what’s what when you look up.

  17. Franco

    Hi all!!!
    I love this site! I hope we’ll have at least a day of clear weather to see the duet :-) here has been fraking cloudy for 2 months.. in Milan, it’s a pity cause mi window (&my telescope) points to S/W,
    seeya!!
    bye from Italy

  18. Josh

    “Binoculars might help, but make sure the Sun is gone before scanning for the planets!”

    This is good, rough advice, but the sun is by no means a magical eye-destroyer. If the sun is on the sea-horizon, it’s perfectly safe to look at it directly through binoculars:

    http://mintaka.sdsu.edu/GF/vision/Galileo.html

  19. andy

    then she was like “ok, i’m going back to watching One Tree Hill”… women!

    Ah, the stench of cheap misogyny.

  20. Josie

    @ andy

    Maybe he just needs a bigger telescope to keep her interested longer :)

  21. Sili

    But the smallest planet isn’t Mercury it’s Pluto, no, Makemake, no, Haumea no, *Sedna* isn’t it?

    After all, dwarf planets are still planets just as dwarf stars are still stars & those who say different can take a long walk off a short jetty far as I’m concerned!

    If you wanna be cute, please note that Ceres is a mere 950 km in diameter.

  22. Joseph G

    @21 Josie: Size isn’t that important – it’s how you mount it that counts.

  23. Messier Tidy Upper

    @22. Sili : Oops! D’oh! Yes indeed. Well spotted. I should’ve thought of that. :-)

    I have seen Vesta (530 km mean diameter) suggested for dwarf planet status as well too – it would be “round by own gravity” but for its giant south polar crater, which it can hardly be blamed for!

  24. Stephanie

    Thanks for the info. I am currenly working on a science journal as we speak and am excited to see the two planets and be able to include this in my sightings.

  25. Claire

    Yes! That’s just how I saw Jupiter and Mercury this evening at about 18.50 GMT in England. Mercury looked quite bright, the brightest I’d ever seen it.

    Mercury is the smallest planet. The other bodies referred to, ie Ceres, Pluto, Sedna, etc are dwarf planets to distinguish them from the larger 8 planets

  26. Sudro

    Unfortunately, too much low cloudiness on the Pacific horizon tonight in SoCal. I’ll hope for better luck tomorrow!

  27. Josie

    @Sudro –in San Diego we got a brief glimpse of them between clouds but they were practically on top of each other. Here’s hoping for a clear horizon tonight!

  28. that is so cool but as time goes by in 200 years you will see a light in the sky as clouds block the light it seemes to get darker and lonly but you need to know that the time will go by fast god will make time go as fast as you know it i am 9 years old

  29. Conshycrush

    Size isn’t that important – it’s how you mount it that counts

    That’s funny!

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