Observation of Comet Hale Bopp from Hawaii in March 1997 – by Albert Lim

I) Background Information

When news broke that a new comet was discovered on the morning of 23^rd July 1995 near M70 in Sagittarius by 2 independent observers, my pulse quicken and I asked myself the same question I did many years ago - is it going to be another disappointment like Comet Kohoutek ( C/1973 E1 ) in 1974 ? Initially called “Comet of the Century” in magazines such as the Reader’s Digest, Comet Kohoutek was barely visible to the naked eye from Singapore skies at perihelion.  Even Halley’s Comet  (1P/Halley 1985-86 ) did not live up to what many observers had hoped for. Would this newly discovered comet outperform Comet West ( C/1975 V1) which put on the best visual display to date when it became as bright as Sirius in the morning sky of  February to March 1976?

The new comet was named Comet Hale-Bopp or C/1995 O1 ( C denotes orbital periods greater than 200 years while O1 implies that it is the first comet to be discovered in the second half of July of 1995 ). It was discovered independently by astronomer Dr. Allan Hale who holds a Ph.D in astronomy since 1992 from New Mexico State University in Las Cruces and Mr. Thomas Bopp who is an amateur astronomer for over 25 years who was observing from a spot in the Arizona desert near Stanfield some 90 miles South of Phoenix. Both discoverers were using Newtonian telescopes in excess of 40cm aperture.

The discovery of Comet Hale-Bopp was announced in IAU circular number 6187 dated 23^rd July 1995 with the comet reported at magnitude 10.5 to 10.8 and slowly moving West North West. Although J. Stephen’s name was also mentioned jointly with T. Bopp’s in this IAU circular as an observer, the new comet was named only after its discoverers Hale and Bopp.

By 24^th July 1995, it was discovered that Comet Hale-Bopp displayed no parallax from simultaneous observations made from Japan and Australia. It became established mid-day 26^th July 1995 that the new comet was well beyond the orbit of Jupiter at 6.7 AU !
( with refined computation from 208 precise measurements, Brian Marsden was later    to confirm in August 95 that the comet was in fact at a distance of slightly over 7 AU at the time of discovery ! ) This suggested incredible intrinsic brightness. Perihelion estimated at that time to be early 1997. The big question then on everyone’s mind was would this comet possibly become brighter than Venus and become one of the brightest comet in recorded history ?

It was discovered about end July or early August 1995 that renown comet observer Rob McNaught actually had an image of Comet Hale-Bopp when it was still at a distance of over 13 AU taken with a telescope at Sliding Spring Observatory in NSW, Australia dating back to 27^th April 1993 ! About this time, Brian Marsden issued another IAU circular providing Rob’s 1993 position of the comet. It was also established that Comet Hale-Bopp was not a new comet from the Oort Cloud but have orbited around the sun at least once before. This implied better chances of it being spectacular during perihelion.

By March 1996, it was established that Comet Hale-Bopp will pass perihelion 3.30 UT on April 1^st 1997 at 0.914 AU or 137 million kilometers but its closest approach to the Earth will occur on the 22^nd March 1997. Even so, it would be at a substantial distance of 1.315 AU or 197 million kilometers. By December 1996, Brian Marsden of the Central Bureau for Astronomical Telegram had computed and concluded that the orbit, absolute initial brightness, perihelion distance and placement, inclination and period of Comet Hale-Bopp is extremely similar to the Great Comet of C/1811 F1 and there is a good possibility that Comet Hale-Bopp would perform spectacularly as C/1811 F1 did.

In conclusion, Marsden stated that Comet Hale-Bopp probably passed its last perihelion 4200 years ago and following it’s 1997 apparition, is not expected to return to the inner solar system until some 2,380 years after.

Orbital elements of Comet Hale-Bopp computed based on 1522 precise positions obtained during the period of 27^th April 1993 to 16^th December 1996 were as follows :

The whole world predicted, waited and anticipated this spectacular comet. I was no exception - plans were well on the way by early 1996 to observe Comet Hale-Bopp.

II) Where and When To Observe Comet Hale-Bopp ?

Using Dance of the Planet Software and inputting the above orbital elements, I was able to produce an accurate path of Comet Hale-Bopp in 1997 through the sky. This was circulated through to the Press for publicity as well as to members of The Astronomical Society of Singapore ( TASOS ).

The path showed that from March to April 1997 when Comet Hale-Bopp is nearest Earth and passing perihelion, it will be in the Northern part of Andromeda moving through Perseus before finally reaching Taurus by end April 97. Specifically, it is within approximately 5 degrees North of the great M31 galaxy between 25^th and 26^th of March 97 and will proceed to pass within approximately 2 degrees of M34 on the 6^th and 7^th of April 97. We desperately needed to catch the comet in March of 1997.

What was terrifying to amateur astronomers in Singapore was that the visibility for Comet Hale-Bopp in March 97 was such that those living South of the Earth’s equator would not see the comet at all because it rises after and sets before the sun does. ( Although we are not South of the Equator, Singapore is only 1 degree plus North so the implication is practically the same. ) The only way we can hope to observe this once in a lifetime comet we reasoned was to move North. The question is where to ?

We knew that at 45 degrees North and above in March 97, the comet would be circumpolar and visible throughout the night. The lower the latitude, the more correspondingly less time we have to observe it. Ideally, the best site should be situated 45 degrees or more North. A variety of factors such as working leave,  available sites and phases of the Moon affect the final decision for the observation site. We decided the ideal site would be Mauna Kea on Big Island, Hawaii targeted at 14^th - 16^th March 1997. While it is not as far North as I like it to be, I was sure that the high elevation ( 13,796 feet ! ) plus the almost certain good observing conditions and excellent transparency would ensure that we would not miss this spectacular comet. Besides we were dying to visit our dream observatories on that famous mountain !

We finally made the trip to Mauna Kea in mid March 1997. 18 TASOS members form the comet observing team and it turned out to be a most memorable trip. In addition to observing, documenting and securing hundreds of spectacular images of Comet Hale-Bopp, we also had the opportunity to observe with Mr. Stephen James O’Maera – author of Sky books “Messier Objects” and “Caldwell Objects”. James O’Maera also writes for Sky & Telescope and is the first observer on Earth to glimpse Halley’s comet visually on its last apparition. He conducted an interview with us and later wrote an article about our trip to Hawaii to observe Comet Hale-Bopp. This article was published in the July 1997 issue of  Sky and Telescope and is titled “Seeking the Soul of the Night” – it was reproduced with permission on TASOS website at http://tasos.org.sg.

III) Observational Information

IV) Subject Information ( as of 15^th March 1997 )

V) The Observation Timing Decision

Our targeted date 14^th - 16^th March 1997 was selected in part due to the school holidays, I had wanted my children ( and wife ) who were schooling to come along to Hawaii to view this spectacular comet. Otherwise observing the comet on the 9th March ( about a week earlier than 14^th of March 97 ) would be more favourable since the comet would actually be higher in the sky and for longer periods. The first day Moon on the 9th March 97 would pose no problem since crescent moons set within a few hours of sunset. What pushed the final decision for 14^th - 16^th March 97 was the fact that it was much nearer to the 22^nd March 97 date when the comet would be closest to the Earth. The quarter Moon on the 15^th March 97 sets about midnight and should not interfere with early morning observations of the comet.

VI ) Comet Hale-Bopp Observational Data 14^th - 16^th March 1997

a)  Photographic Documentation - Our comet team acquired over a hundred images of Comet Hale-Bopp during this expedition. Plans to capture the comet’s inner nucleus utilising our SBIG ST-4 as imaging cameras was unsuccessful due to failure of the ST-4 – possibly due to the power supply at extremely cold temperatures. ( minus 10 degrees C ).

Comet Hale-Bopp from Hawaii 14^th March 1997.
Time : 0525 - 0535 am local time. 10m exposure.
Genesis 4 inch 540mm FL on TS EM200 Mount
manual guided on comet nucleus. Nikon F3 and
Kodak P1600 slide pushed ASA800. Albert Lim.
Other Comet Hale-Bopp images from Hawaii is
available our TASOS website.

Comet Hale-Bopp displaying dust and blue Ion tails
on 14th March 1997. Time : 0520 hrs - 0535 hrs.
From : Mauna Loa Volcano 11,000ft. Exposure :
15 mins on Kodak P1600 slide, processed at ASA
800. Carl Zeiss 45mm F2.8 Yashica FX2000 Body.
Guided on Takahashi EM200 Mount. Astrophoto
by : Mr. Soh Kim Mun.

Wide Field Comet Hale-Bopp and North America
Nebula on 13th March 1997. Time : 0515- 0530 hrs.
From : Kilauea Volcano Summit 4,200ft. Exposure :
15 mins on Kodak P1600 slide, processed ASA 800.
Olympus 28mm set F2.8 on Olympus OM1 body.
Guided with Celestron C5+ and SBIG ST4.
Astrophoto by : Mr. Ang Poon Seng

b)  Visual Observations  
Total visual magnitude estimate of the coma was done using the Morris method. We had to defocus substantially before the comet appears uniform in brightness because of its extremely bright nucleus. It was very difficult to do this at high powers with telescopes. Comparisons were thus made using low power binoculars because of the coma’s size and brightness. Comparisons made with defocused Deneb and Vega ( magnitudes 1.25 and 0.03 respectively ) showed that Comet Hale-Bopp was much brighter. We had problems as there was no brighter stars for comparison so we had to resort to Mars and Jupiter ( -1.2 and -2.0 respectively ) to estimate m1 for the comet. “Winter” Atmospheric Extinction factor of 0.14 based on 3,000m elevation and z = 20 degrees altitude for the comet to horizon. The estimate made by an individual observer ( i.e. myself ) is - 0.85 for the 15^th of March 1997. This translates to 0.71 magnitude after taking off the above 0.14 magnitude. Since the elevation is closer to h = 4 instead of h = 3 ( i.e. 4,000m instead of 3,000m elevation) and there are no factors available for h=4, I am tempted to interpolate the extinction factor as 0.13 since h = 1 is 0.20, h = 2 is 0.16 and h = 3 is 0.14. If such is the case, then the reported magnitude for 15^th March 1997 should read really read - 0.72 instead of - 0.71.

The cometary nucleus was extremely bright almost starlight and clearly distinct within its circular coma. The degree of condensation (DC) was estimated at 7. No spikes were observed in the nucleus but there were at least 3 distinctive envelopes shaped like shock waves around the pseudonucleus. These 3 envelopes seem to go a quarter arc around the nucleus and have diameters estimated via a Celestron Microguide eyepiece at 20”, 40” and 75”. (The method of timing a star cross its nucleus was not successful due to technical reasons) The innermost envelope seems like it is about to split into 2 fountains. It is strictly incorrect to describe these as shock waves ( such as caused by rapid motion of the comet ) since they are results of active vents on the comet’s nucleus.

The dust tail branch off from the comet’s head at an approximate 30 degrees angle from the ion tail. The ion tail was distinctly blue and less obvious than the dust tail with the naked eye. It was however clearly visibly in 7 x 50 binoculars extending as much as 6 degrees. The brighter dust tail exhibited more than a dozen streamers. Photographic documentation encountered many problems due to power and equipment failure of the ST-4 autoguider. Manual eyeball guiding on the comet’s head which was larger than the crosshair circle unlike normal stars presented a different challenge. Despite the difficulties and extreme cold and altitude, we really enjoyed the crystal clear superb viewing and conditions on Mauna Kea where Comet Hale-Bopp was truly a beautiful sight to behold.