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A Christmas Star for SOHO

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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.

Above: On May 15, 2000, SOHO's wide field coronagraph recorded this image of the Sun surrounded by Mercury, Venus, Jupiter and Saturn. A well-known asterism The Pleiades is also visible in the upper left of the image. The blue disk blocks out the Sun's bright light; the white circle near the center shows the true size of the Sun. At 1030 UT on May 17, Venus and Jupiter will be less than 0.01 degrees apart.


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"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.

Watch the Venus-Jupiter conjunction at the SOHO Realtime Images page!

Above: This computer animation shows the relative positions of Jupiter and Venus as seen from Earth on May 17, 2000. The six-frame sequence begins at 0830 UT and ends at 1330 UT. The minimum separation between the two planets occurs near 1030 UT. Also shown are the Galilean satellites Io, Europa, Ganymede, and Callisto. The horizontal field of view is approximately 15 arcminutes (the angular separation between Callisto and Jupiter is approximately 7').

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.

Web Links

SOHO home page -real-time images, screen savers, and more

The Star of Bethlehem: An Astronomical and Historical Perspective -- by Susan S. Carroll

Planetary Alignments in 2000 -- from the Griffith Observatory

Venus enhances SOHO's unique picture of planets beyond the Sun -- from the European Space Agency

SOHO Hotshots -- from NASA


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