A quote from David Levy (comet discover, comet observer, writer and my very good friend): "Comets are like cats. They have tails, and they do precisely what they want."
How to Find Hale-Bopp (Without Charts) (3/19/97)
Finder Charts for Hale-Bopp from
Dale Ireland (3/6/97)
Visibility of Hale-Bopp from the
Southern Hemisphere (3/6/97)
How to Photograph the Comet (3/19/97)
General Information on Comets
The Discovery of Hale-Bopp
The Orbit of Hale-Bopp (3/7/97)
How Big is Hale-Bopp?
Dust Jets from Hale-Bopp's Nucleus
How fast is Hale-Bopp's Nucleus Rotating? (3/14/97)
What are the Hoods or Ripples Seen in Hale-Bopp's Coma? (3/14/97)
How Bright will Hale-Bopp Become? (3/14/97)
Hale-Bopp's light curve! (3/14/97)
What to Expect?
Links to Images (1/31/97)
Hale-Bopp and the Total
Solar Eclipse of March 9, 1997 Results (3/18/97)
Links to Other Hale-Bopp Home Pages (2/25/97)
Little Green Men and Other Hoaxes
Rather than redo what other people have already done, links are provided below to some excellent sources of general information on comets. These include:
the comets section from The Nine Planets and
the comets section from Views of the Solar System
This comet was discovered on July 23, 1995 UT (Universal Time = Greenwich, England time, which astronomers use as a common time for reporting observations) by Alan Hale, New Mexico, and Thomas Bopp, Arizona. This is the first discovery for both, although Alan Hale is one of the top visual comet observers in the world having seen about 200 comet apparitions. The discoverers' comments about their discovery can be found here.
The orbit of this comet is of long period (~4200 years since the last appearance and because of gravitational tugs by the planets, particularly Jupiter, the next appearance will be in about 2380 years). It has been through the inner solar system before. That is, it is not a new comet from the Oort Cloud. Its orbit is a very long, stretched out ellipse and the comet is part of our solar system in orbit around our Sun.
The comet reaches its closest point to the Sun (perihelion) on April 1, 1997. At that time, it will be about 0.914 astronomical units from the Sun (one AU = about 93 million miles or 150 million kilometers -- the distance between the Sun and the Earth) or roughly 85 million miles (138 million kilometers) from the Sun. This is not a particularly close approach to the Sun. Some comets, like Comet Ikeya-Seki in 1965, have literally skimmed the surface of the Sun (and others have actually gone right into the Sun). Nonetheless, any comet that comes within 1 AU of the Sun has a chance to put on a nice show.
It has been suggested by some people that this comet may pose a threat to the Earth...
The comet will make its closest approach to the Earth on March 23, 1997. At that time, the comet will be more than 120 million miles (194 million kilometers) from Earth -- not even a very close approach! Will the comet "cross" the Earth's orbit? Well, yes and no...the comet will come closer to the Sun than the Earth, but it will never actually physically cross any point in space that is occupied by the Earth -- it can't hit the Earth!
The orbit is inclined nearly 90 degrees from the ecliptic (the plane of our solar system in which the planets orbit). The comet will come up from the south, go over the top of the Sun and then plunge down again. This means that the comet will be best seen from the Southern Hemisphere (and lower Northern latitudes) EXCEPT when it is expected to be at its brightest. In March and April 1997, it will only be easily visible from the Northern Hemisphere.
A note about comet orbits...as new positional observations are obtained, the orbital parameters of a comet, any comet, are updated and they will change - typically by a small amount. This does not mean that the comet has undergone a "course correction" as has been suggested in some postings on USENET.
Note: the "recurrence period" that is discussed below (and some time ago) is not the rotation period of the comet's nucleus. If the comet's rotation is complex... that is it rotates on more than one axis (this is called precession), the comet can have a shorter "rotation period"...Hale-Bopp does.
There have been jet(s) of dust (and gas) detected from the comet's nucleus by professional telescopes since its discovery and more recently by amateur astronomers using large telescopes. Such jets are not unusal, but it is rare for a comet this far from the Sun to display them. The jets can tell us a lot about the rotation of the comet's nucleus.
On IAU Circulars 6223 (September 8, 1995), 6240 (September 29, 1995), and 6248 (October 20, 1995), Z. Sekanina, Jet Propulsion Laboratory, discusses the observed jets and what it means with respect to the rotational period of the nucleus. His results indicate that the "rotation" period is indeterminate, but not greater than ten days. However, the nucleus is apparently not only spinning on its axis, but the axis is also precessing. This type of complex rotational state was also suspected for Periodic Comet Halley in 1986. Sekanina points out that the approximate time between observed jet events was five weeks between the first two events, but only half this for the last two events. Thus, the recurrence period of the jet is probably 18 days (longer than the pure rotation period because of the precssion of the axis). This implies that the jet does not always develop given the five weeks (and not 18 days) between the first two events.
Sekanina states "One can infer that C/1995 O1 might be (relatively) CO-rich and, at the same time, dust-rich. If such CO supplies would last until perihelion, then the comet could indeed become very bright. Yet, it does not have to have an excessively large nucleus." CO is carbon monoxide, which can sublimate (turn from solid to gas) at great distances from the Sun. When comets are closer to the Sun, water ice (H2O) is normally the primary component that sublimates.
In a paper entitled "Activity of Comet Hale-Bopp (1995 O1) Beyond 6 AU from the Sun", submitted to Astronomy & Astrophysics, Sekanina uses visual nuclear (m2) magnitude estimates by seven visual observers (Bortle, Hale, Mikuz, Modic, Morris, O'Meara, Roques, and Seargent) and one CCD observer (B. E. A. Mueller) to determine the time of the on-set of the August jet.
Mark Kidger, Instituto de Astrofisica de Canarias (Spain), has modified his views on the rotation of the nucleus of Hale-Bopp. His current views (December 19, 1995), which are still in disagreement with Sekanina, can be found in this link.
Mark Kidger, Instituto de Astrofisica de Canarias (Spain), provides comments on the recent near-nucleus activity of Hale-Bopp (6/11/96)
IAUC 6583 (March 11, 1997) reports that L. Jorda, Max-Planck Institut fur Aeronomie; J. Lecacheux, Observatoire de Paris, Meudon; and F. Colas, Bureau des Longitudes, have determined a rotation period of 11.47 +/- 0.05 hours, but show a periodic oscillation of this period between 11.20 +/- 0.10 hr and 11.65 +/- 0.10 hr with a superperiod of 22 +/- 2 days. You can see the rotation from an animation of their images.
We are apparently looking down on the pole of Hale-Bopp's nucleus. As it spins about twice a day, the dust jets shoot out dust. This dust forms arcs as the nucleus spins and the dust moves away from the nucleus. These arcs, hoods or ripples are the end result.
In order to follow the progress of the comet's brightening, take a look at the comet's light curve.
A wonderful collection of images has also been compiled by Ron Baalke (JPL).
The Stuttgarter Hale-Bopp Homepage (in German) has recent images and observations of Hale-Bopp.
Y. Chimura in Japan has an extensive collection of Hale-Bopp images (text in Japanese).
Abrams Planetarium (Michigan State University) provides more specific information on where to find the comet for Northern Hemisphere Observers.
Unless otherwise noted, these finder charts have been supplied by Dale Ireland. Dale's astronomy page (comets, eclipses, etc.) is excellent.
Hale-Bopp will pass a number of nebulae and clusters as it moves through the sky. The following are detailed charts from Dale Ireland of some of these close passes. (More will be added later.)
Additional charts can be found on Charles Boley's Comets On-Line.
For the more experienced observer, the ephemeris page provides positions for Hale-Bopp and other comets. The comet's position can then be plotted on your own star charts for a given night.
Comet Hale-Bopp may be visible during the total solar eclipse that runs through Mongolia and eastern Siberia on March 9, 1997. Further details are available through this link.
Observation from the eclipse...
1997 Mar.10.01UT: m1=-0.2, DC=8.5, Tail 2deg...6x30B....Vladimir Dinets (Tynda Highlands: 55,5deg.N;126deg.E) [Solar eclipse, central path, 3 min. Weather conditions as if specially designed. Corona typical for low activity, but very symmetrical and beautiful,resembling the vulture-winged Sun of Ancient Egypt paintings. Comet not well seen due to red glow on the horizon]
Ron Baalke (JPL) maintains a comprehensive list of links to other Hale-Bopp Pages.
The Central Bureau for Astronomical Telegrams has a wonderful information sheet on Hale-Bopp (and comets in general).
Russell Sipe has an excellent Hale-Bopp Page
Sky & Telescope has an excellent page on comets that includes information on Hale-Bopp.
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Charles S. Morris / csm@encke.jpl.nasa.gov