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Information on Comet Hale-Bopp for the Non-Astronomer

Last Updated: 17 April 1997

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."

What's new? Check out the following:

Ode to Comet Hale-Bopp (4/15/97)
How to Find Hale-Bopp (Without Charts) (3/19/97)
Finder Charts for Hale-Bopp from Dale Ireland (4/15/97)
Visibility of Hale-Bopp from the Southern Hemisphere (4/15/97)
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! (4/17/97)
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

General Stuff about Comets

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
In addition, this page provides a list of definitions that should prove useful.

The Discovery of C/1995 O1 (Hale-Bopp)

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 C/1995 O1 (Hale-Bopp)

At perihelion on April 1, 1997 (13 Kbytes)
Courtesy: Dale Ireland

Relative postion of the comet and Earth om March 1, April 1, and May 1, 1997 (73 Kbytes)
Courtesy: Eric Frappa, Saint-Etienne Planetarium, France

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...

This comet will NOT hit 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.

How "big" is it?

There have been reports that this comet is very large. Actually, the heart of the comet, the nucleus, is obscured by the dust and gas that forms the head of the comet. Nobody knows how large the nucleus is. We can't see it! The nuclei of comets range in size from a few miles (kilometers) or smaller to over 100 miles (~160 kilometers) in diameter. The brightness of the comet is not always directly related to the size of the nucleus. This is because typically only a fraction of the surface of a comet's nucleus is active. It is possible that this comet has a small nucleus with most of its surface emitting dust and gas. It is also possible that this comet has a large nucleus with only a small active region. Recent estimates of the nucleus size, based on the amount of material being generated by the comet, put the nucleus at about 40 km (about 25 miles) in diameter. However, this is just an educated guess. For comparison, Comet Halley's nucleus, which we did see via spacecraft observations, looked like an irregular potato 8 x 8 x 16 km (5 x 5 x 10 miles).

The coma or head of a comet, the dust and gas that surrounds the nucleus, can reach several 100,000 kilometers in diameter. This size varies with the comet's distance from the Sun. The tail of a comet, like Hale-Bopp, can reach many millions of kilometers long.

Jets Coming from the Nucleus

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)

How fast is Hale-Bopp's Nucleus Rotating?

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.

What are the Hoods or Ripples Seen in Hale-Bopp's Coma?

(3/14/97)

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.

How bright will it get in March and April, 1997?

It now seems likely that the peak brightness of the comet will be about magnitude -0.8 magnitude). This means that the comet, which will look like a bright, fuzzy, star with a tail low in the northwest sky in the evening, should be brighter than any star in the evening sky except Sirius and the planet Mars.

In order to follow the progress of the comet's brightening, take a look at the comet's light curve.

What to expect:

Late April - June 1997: In late April, the Moon will interfere. Comet will move south and closer (in the sky) to the Sun. It will also fade significantly, but the tail development should peak in May or June. It will be lost by the general public in the Sun's glare. Experienced observers might be able to follow it. Northern Hemisphere observers lose the comet during May.

July - September 1997: Moves away from (but is still close to) the Sun in the morning sky. Comet is moving rapidly towards the south and continues to fade.

October - December 1997 - Comet is lost from naked eye visibility. (It may be lost earlier due to its location close to the Sun.) Comet continues to be a binocular object for Southern Hemisphere observers.

What does it look like?

Images of the comet can be found here.

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).

How Can You Find the Comet?

The comet can now be seen in the evening sky. As it gets dark (and you see the stars come out), look towards the northwest (1/8 turn towards the north from where the Sun set.) The comet will be ~25 degrees above the horizon (~2.5 fists held at arm's length) and the brightest object in that area of the sky.

Abrams Planetarium (Michigan State University) provides more specific information on where to find the comet for Northern Hemisphere Observers.

Finder Charts for Hale-Bopp

Unless otherwise noted, these finder charts have been supplied by Dale Ireland. Dale's astronomy page (comets, eclipses, etc.) is excellent.

Finder chart for C/1995 O1 (Hale-Bopp) provided by Dale Ireland. The major constellations and stars are indicated. (Click on image for larger view.)
These charts, which were provided by Dale Ireland, show the where Comet Hale-Bopp is in the sky at one hour after local sunset for observers at 40, 20, 0 degrees latitude. (Click on image for larger view.)

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.

o Chart showing Hale-Bopp going past M-14 October 28 - November 1, 1996
o Chart showing Hale-Bopp going past M-71 February 6-7, 1997

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.

Viewing from the Southern Hemisphere

These charts, which were provided by Dale Ireland, show the where Comet Hale-Bopp is in the sky at one hour after local sunset for observers at -20 degrees latitude. (Click on image for larger view.)
These charts, which were provided by Dale Ireland, show the where Comet Hale-Bopp is in the sky at a specific time (6pm local standard time) for observers at 30 and 35 degrees South latitude. Note that even five degrees further south hinders the viewing of the comet. (Click on image for larger view.)

Comet Hale-Bopp and the Eclipse of March 9, 1997

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]

Links to Other Hale-Bopp Home Pages

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.

AGRUPACIÓN ASTRONÓMICA DE GRAN CANARIA maintains a page that provides information on Hale-Bopp in Spanish.

Little Green Men and Other Hoaxes

It seems that whenever there is a newsworthy comet someone takes advantage of it and promotes ideas that simply are not true. Hale-Bopp has had more than its share of hoaxes. Hale-Bopp is only a comet...an intrinsically bright comet, but only a comet. It has been suggested that an object is moving with the comet...this isn't true. These images (or their interpretation) are hoaxes. See the following links for a discussion of the subject.

o Link to Russell Sipe's page on the subject
o Link to Alan Hale's explanation of the "object" (on Russell Sipe's page)

Go To:

Comets Currently Visible
Recent News and Observations
Comet Light Curves
Ephemerides for Current Visually Observable Comets
Comet Definitions
Comet Images
Other Pages Featuring Comet Images
Comet Observation Home Page

Comments?

Charles S. Morris / csm@encke.jpl.nasa.gov