NASA Science News

A Christmas Star for SOHO

The planets Venus and Jupiter will pass less than 42 arcseconds apart on May 17. Because the pair is so close to the Sun, only the Solar and Heliospheric Observatory will have a good view of the close encounter.

May 16, 2000 -- If someone could turn off the Sun for a while on Wednesday, star gazers would be treated to a remarkable sight. The two brightest planets, Venus and Jupiter, will pass less than 0.01 degrees apart at 1030 UT on May 17. Unfortunately, the close encounter will take place just 7 degrees from the bright Sun, making it impossible to see with the naked eye.

Nevertheless, you can still monitor the encounter thanks to the ESA/NASA Solar and Heliospheric Observatory (SOHO). SOHO has an advantage over most stargazers. Coronagraphs on the satellite can block out the Sun's bright light in order to see nearby stars and planets as well as the Sun's faint corona. The conjunction will be easy to see in images from SOHO's wide field coronagraph that are posted on the SOHO realtime images web page ( "If Jupiter and Venus were farther from the Sun on May 17, the conjunction would be a real eye-catcher," says astronomer Dr. George Lebo, a 2000 Summer Faculty Fellow at the Marshall Space Flight Center. "The human eye can distinguish objects separated by angles greater than 50 arcseconds, but Venus and Jupiter will only be 42 arcseconds apart. At closest approach the pair would appear to merge into a single brilliant star." This close conjunction has already been compared to the 2 B.C. conjunction of the same planets that is often identified as the "Christmas Star" reported in the book of Matthew.

In "The Star of Bethlehem: An Astronomical and Historical Perspective," Susan S. Carroll writes:

On June 17, 2 BC, Venus and Jupiter joined .... in the constellation Leo. The two planets were at best 6" (arcseconds) apart; some calculations indicate that they actually overlapped each other. This conjunction occurred during the evening and would have appeared as one very bright star. Even if they were 6" apart, it would have required the sharpest of eyes to split the two, because of their brightness.

The Conjunction at a Glance

  • Jupiter and Venus will pass 42 arcseconds apart at 10:30 UT on May 17.
  • Both planets will be full phase with apparent polar diameters of 9.8 and 30.8 arcseconds.
  • At closest approach their limbs will be separated by only 22 arcseconds.
  • The Venus-Jupiter conjunction takes place 7 degrees from the Sun.
  • The last time Jupiter and Venus were so close was in 1859; the next time will be in 2065.

    Venus-Jupiter conjunctions like the one on May 17, 2000, are not terribly rare, notes John Mosley of the Griffith Observatory in an essay on Planetary Alignments in 2000. According to Mosley, the last time Venus and Jupiter were closer than on May 17, 2000 (separated by less than 42 arcseconds) was at 3:47 on July 21, 1859, when their centers were 32 arcseconds apart (there was no partial occultation). The next time will be at 12:45 on November 22, 2065, when their centers will be 16 arcseconds apart and the northern edge of Venus passes in front of Jupiter.

    Although Venus and Jupiter will appear to be very close together on May 17, there's no danger of a collision. The two are really very far apart. Venus will be 257 million km from Earth, while Jupiter will be 896 million km away. The two are separated from each other by a comfortable 639 million km.

    As Venus passes by Jupiter on May 17 the five classical planets (Mercury, Venus, Mars, Jupiter and Saturn) will span just 19 25'. The cluster is too near the sun for naked-eye observations, but it's perfect for SOHO coronagraphs, which will be able to see all of the planets except Mars.

    SOHO is a cooperative project between the European Space Agency (ESA) and NASA. The spacecraft was built in Europe for ESA and equipped with instruments by teams of scientists in Europe and the USA.

    Space Weather News for May 16, 2000

    On May 15 a coronagraph on the ESA/NASA Solar and Heliospheric Observatory captured rare images of a full halo coronal mass ejection with 4 planets and the Pleiades in the field of view. Material from the eruption could arrive in the neighborhood of Earth on May 17 or 18.

    For more information and animations, visit


    May 15, 2000

    Venus enhances SOHO's unique picture of planets beyond the Sun

    Mercury, Venus, Jupiter, Saturn and the Sun all appear in the same image sent to Earth today (15 May) by the SOHO spacecraft. The picture with four planets is another scoop for SOHO.

    More at:

    NASA Science News for March 30, 2000

    Next Thursday, April 6, three planets and the thin crescent Moon are going to put on a memorable sky show when the quartet converge inside a circle 9 degrees across. The grouping is just the prelude to a grander alignment of planets on May 5, 2000. Is doom at hand, as many mystics assert?

    Find out by reading the FULL STORY at Planets for Dessert

    Also, for kids and kids-at-heart, a younger person's version of this article is available at the NASA Kids web site:
    The Planets Line Up

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