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New Comet to be Naked-Eye Next July!

The LINEAR minor planet search machine has turned up a new comet. Dubbed C/1999 S4 (Linear), it is coming in from the outer Solar System to round the Sun in mid-July, 2000. When closest to the Sun, Linear will be just inside the orbit of Venus. At almost the same time, it will be at its closest point to the Earth. Even though the comet will be between the Earth and Sun, it will be high enough above the ecliptic to give northern hemisphere observers a good view of Linear.

C/1999 S4 is already north of the ecliptic and will continue to slowly drift northward as it hurtles toward the Sun. Shortly before Christmas, it will stop moving north and begin the southward leg of its orbit. The Earth and comet will both be heading in roughly the same direction, but toward opposite sides of the Sun. As the Earth moves to one side of the Sun and the Comet to the other, the comet will drift through the evening sky toward the Sun, but staying well north of it. Swinging over the Sun in late April, Linear will then appear in the morning sky in late May. Linear will continue to get higher in the morning sky as it comes toward us from the opposite direction of our motion around the Sun.

In late June, Linear reaches its highest point in the morning sky and begins to retreat toward the Sun. As it approaches both the Earth and Sun, it will be visible all night low in the northern sky. After perihelion, C/1999 S4 will rapidly move west of the Sun to become an evening object. It will also start diving southward, becoming no longer circumpolar. This should be the time of its best display for northern hemisphere observers. By the middle of August, Linear will have disappeared below the western horizon. It will move into the constellation Corvus and remain there through the remainder of the year.

How bright will Linear get? It is far too early to tell, but may be as bright as third magnitude. Only time will tell. It is currently 16th magnitude and slowly brightening. Right now, Linear has a tail that is around twenty seconds of arc long in p.a. 220° and a coma of 10". Only time will tell what its tail will be like at perihelion.

C/1999 S4 was discovered by the LINEAR machine on September 27 and noted to be non-asteroidal by D. Durig (Sewanee, TN) and by J. Ticha and M. Tichy (Klet). The Central Bureau for Astronomical Telegrams of the International Astronomical Union made the announcement on Circular 7267. The following parabolic orbit is from Circular 7335 (1999 December 18) (and MPC 37026):

    T = 2000 July 26.1053 TT         Peri. = 151.0719

                                     Node  =  83.1520  2000.0

    q = 0.763984 AU                  Incl. = 149.3583

This looks like a gem of a comet for northern hemisphere observers that should have a nice tail and be reasonably bright. Start planning your observing  and photography now!

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This page is maintained by Matt Ganis for the Astronomical League. Comments, corrections, and suggestions can be addressed to This page last updated January 1, 2000.
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