Information on Comet Hale-Bopp for the Non-Astronomer

Last Updated: 6 February 1997

A quote from David Levy (comet discover, comet observer, writer): "Comets are like cats. They have tails, and they do precisely want they want."

What's new? Check out the following:

How to Find Hale-Bopp (Without Charts) (2/5/97)

Finder Charts for Hale-Bopp from Dale Ireland (1/29/97)

General Information on Comets

The Discovery of Hale-Bopp

The Orbit of Hale-Bopp

How Big is Hale-Bopp?

Dust Jets from Hale-Bopp's Nucleus

How Bright will Hale-Bopp Become?

Hale-Bopp's light curve! (2/6/97)

What to Expect?

Links to Images (1/31/97)

Hale-Bopp and the Total Solar Eclipse of March 9, 1997

Links to Other Hale-Bopp Home Pages

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

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)

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

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 bright will it get in March and April, 1997?

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

What to expect:

February - early March 1997: Comet is low in the east just before dawn. The comet is a fuzzy star to the naked eye. First-time observers may need assistance finding the comet, particularly early in the period. Sharp-eyed observers in dark skies might see the tail with the naked eye. Binoculars show a parabolic shaped coma and several degrees of tail.

late March - early April 1997: Comet should be at its best. It is expected to be near its peak brightness (~0 magnitude), and is at its farthest declination north. The best dates for observing the comet should be March 26 - April 12. During this period the Moon will not interfere (significantly). The comet will be in the northwest after sunset. The comet should display a noticable tail that extends for more than ten degrees.

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.

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. Northern Hemisphere observers lose the comet during this period.

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?

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 be currently found by looking east about 30 minutes prior to dawn. Hold your fist at arm's length. The comet is slightly north of due east and about two fists above the horizon. The comet will slowly move northward each day.

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.

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.)

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.

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.

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.

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)

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