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Comet Hale-Bopp

Particle Physics and Astronomy Research Council

Royal Greenwich Observatory
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Special Information Leaflet No. 16: 'Comet C/1995 O1 (Hale-Bopp)'


How, where, what?

Comet Hale-Bopp is named after two amateur astronomers Alan Hale and Thomas Bopp who independently discovered the comet on July 22 1995. At that time it was 560 million miles from the Earth, further than the orbit of the planet Jupiter. It is most unusual for a comet to be discovered at such a great distance from the Sun and immediately astronomers were excited that Hale-Bopp might become the brightest comet in living memory. However, we were wary. Comets often do not live up to expectations.

The nucleus of a comet, often described as a dirty snowball, is typically a few kilometres in size and is thought to arise from the debris remaining after the formatiom of the Solar System. (See the leaflet on Comets).
Comet C/1995 O1 (Hale-Bopp) is typical of the group of comets with very long orbital periods (in this case of order 3,500 years) which originate in the so-called Oort Cloud, a vast spherical cloud of material some 30,000-100,000 Astronomical Units (AU - the Earth-Sun distance) from the Sun. If the orbit of one of these objects become disturbed then it may fall in towards the Sun to be seen by us as a comet. The path of these comets through the Solar System may be inclined at almost any angle to the plane of the Earth's orbit (the ecliptic), unlike the shorter period comets whose orbits more nearly lie in this plane. Comet Hale-Bopp's orbit is inclined at almost 90 degrees to this plane.

As the comet approaches the Sun its outer layers evaporate, and an extended coma develops around the nucleus. Grains of dust are released which lag behind the orbit of the nucleus and become visible by reflected sunlight as the brilliant tail. A gas tail may also be seen, which is ionised material blown outwards from the Sun by the Solar wind.
Astronomers have had unprecendented opportunities to take spectra of Hale-Bopp in the optical, infra-red and radio wavelength ranges as the comet has evolved, and have detected a wide range of moleculular compounds of carbon, hydrogen, oxygen, nitrogen and sulphur.

So far astronomers have not been disappointed. The comet has continued on its way in towards the Sun, travelling at a million miles a day and gradually brightening as it comes.


How and where to see it:

As from mid January 1997 the comet moves from a position to the right of the bright star 'Altair' in the constellation Aquila, slowly moving north and east to the left of the constellation Cygnus over the following month. At the end of February it lies about 15 degrees to the left of 'Deneb' - the brightest star in Cygnus.
In the UK this will mean that it will initially be visible in the morning sky, but from late-February can also be seen in the evening sky.

It will remain low in the west in the evening sky for some weeks, but will be difficult to see unless you have a clear view of the western horizon in an unpolluted sky.

In the morning sky the comet can be seen rising progressively earlier each day; at about 05:30 in mid January, 04:00 at the end of January. By mid February the comet will rise at about 03:00 in the NE and by 06:00 in the morning it will be due East at an altitude of about 30 degrees.

By mid March the comet is just circumpolar - that is, it will not set during the night. Appearing just below the 'W' of the constellation Cassiopeia and in Andromeda it will drop low towards the northern horizon before rising again in the north-eastern hemisphere.

The comet is closest to the Earth on March 22, but at a distance of about 120 million miles, there is absolutely no chance of it colliding with the Earth.
It passes through perigee (ie is closest to the Sun) on April 1 1997. As it approaches the Sun it should get brighter and its tails should develop and this is the time (from late March to early April) when it is expected to be at its best for observers in the UK.


ARVAL's note:
The above paragraphs refer to the northern Latitudes of the UK. For the Equatorial Latidudes of Venezuela, please refer to the weekly pages on Astronomía Caraqueña (in Spanish).


The Moon:

There will be most interference from the Moon, for the comet's observation during the second half of the Lunar cycle, from the Full Moons of January 23, February 22 and March 24.
Note that there is a partial eclipse of the Moon on March 24.



How bright will it become? Will Hale-Bopp become as well known as Halley or Shoemaker-Levy? We don't know, but it might become a spectacular sight in the night sky during the next few months.

[Sky Chart] Click here for a sky chart for the location of the comet:
From May 20 '96 to March 7 '97 (18KB)
From February 15 '97 to April 6 '97 (20KB)
From April 6 '97 to August 14 '97 (19KB)

These charts, produced by Dafydd Wyn Evans are available with better definition here. See, respectively, halebopp1.ps.gz (56KB), halebopp2.ps.gz (61KB) and halebopp3.ps.gz (61KB)


[Hale-Bopp Apparent Magnitude] The varying comet brightness, as observed by a number of different professional and amateur astronomers worldwide and reported in IAU circulars, has been plotted by Geoff Buswell and Robin Catchpole (8 KB).

They have used a simple model to predict how bright the comet may become and this indicates that Comet Hale-Bopp should reach 0.6 magnitude by the end of March.
Click here for more information (Hale-Bopp Brightness page in ARVAL).

There are lots of images of comet Hale-Bopp available. Some of the most spectacular have been taken by Alan Fitzsimmons and collaborators using the British telescopes on La Palma.
See also this Fitzsimmons Image of Comet Hale-Bopp.

Produced by the Information Services Department of the Royal Greenwich Observatory.

Originally written by PJA in August 1995, updated by MJP.
Latest version February 10 1997.

Royal Greenwich Observatory Webmaster:

webman@mail.ast.cam.ac.uk

Updated: March 1 '97, June 23 '14

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