Mars Meets Kaus Borealis Tonight

Mars passes very close to Kaus Borealis (a.k.a. Lambda Sagittarii) tonight. If your skies are clear, take a look during evening twilight about an hour after sunset low in the southwestern sky. Source: Stellarium

Just a quick heads up. I always like to report when a planet and star pair up in the night sky. That happens to happen tonight (Nov. 3) when Mars passes just 1/2° north of Kaus Borealis, the star at the top of the Teapot of Sagittarius.

To spy this temporary “double star”, go out about an hour after sunset and look low in the southwestern sky. That bright red-orange object is Mars. Immediately to its lower left, you’ll see Kaus Borealis deliciously close.

The sky facing southwest on Nov. 18, 1984 shortly before Venus occulted Kaus Borealis. The map shows the sky from Duluth, Minn. during evening twilight. Source: Stellarium

Kaus Borealis, a name combining the Arabic word for ‘bow’ and the Latin word for ‘northern’, refers to the bow of Sagittarius the Archer, the constellation’s formal name. At magnitude +2.8, the star is easy to spot with the naked eye. Since it lies near the ecliptic, the path followed by the Sun, Moon and planets, it’s occasionally occulted by one of these bodies. Back on the evening of November 18, 1984, Venus passed directly over the star and blanked from view for a time. What a scene! Not only did the star blank out, but Jupiter, the sky’s second brightest planet, shone nearby in the same constellation.

Mars won’t occult Kaus, but for a fun activity tonight and over the next few nights, compare the colors of Mars and the star. Kaus Borealis is an orange subgiant star (not quite as big as Arcturus, an orange giant) 2.3 times as massive as the Sun and 52 times brighter. Is Mars more red or are they nearly the same? Have fun getting acquainted with a star we might otherwise ignore were it not for Mars’ proximity.

3 Responses

  1. Kamal Lodaya

    Kaus Borealis, then Kaus Medius, then Kaus Australis. The second picture gives the wrong name. Also, comet Churyumov-Gerasimenko (magnitude 19) on which there is a landing on the 12th, is close to Tau Sagittarii in the “handle” of the teapot..

    1. astrobob

      Thanks Kamal! I heard about the error earlier but when I got home to correct it yesterday evening, the Internet was down and stayed down until 15 minutes ago! It’s fixed now.

  2. Edward M. Boll

    I remember Nov. 18, 1984. That was 6 months before I became involved with astronomy. We had a great delicious harvest dinner at our church. And then I drove 200 miles to the twin cities to visit friends.

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