Pictures

This 10sec exposure of comet Hale-Bopp was obtained by Bill Vacca using the 2.2m telescope of the University of Hawaii telescope at Mauna Kea, through a filter centered on the emission line of the CN molecule, in the near Ultra-Violet.

The field of view of this image is 1.5 arcminute in diameter, 1/20th of the apparent diameter of the moon; it shows only a very small section of the comet which extends on many degrees (North is up, and East is to the left). The image has been processed to correct the sensitivity variations of the CCD detector (this steps are described in another document), then has been enhanced to make the jet structure more visible (a mean radial profile has been partially subtracted). The seeing (degradation of the image quality by the turbulence) was quite high.

Hale-Bopp for the non-astronomer. Hale-Bopp ephemeris.

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.

Hyakutake orbit

ESO Hale-Bopp

Of particular interest in these observations is the evolution of the Sodium emission line observed in the core of the comet. The corresponding spectral region is seen on these spectral tracings [GIF; 12k]. The line is clearly visible on top of the spectral continuum (the reflected sunlight from the dust) in the last two runs (21 and 24 April), just after the discovery of the Na tail (cf. the 23 April Update).

Note that this sodium doublet (in our spectra it is blended due to the low resolving power) seems to appear already in the first spectrum obtained on March 9, 1997. However, its presence in that spectrum may be due to the background light of the close city of Freising or the Munich Airport which were located at angular distances of about 60o and 80o from the comet, respectively. Still, we believe that this is a real emission line from the comet since the exposure times were relatively short (around 80 sec). Unfortunately for this specific observation we have no nearly simultaneous, recorded sky exposure to confirm this assumption. On the following spectra, the Na line is not present (1, 7 and 8 April, 1997).

Kepler's Laws (Honolulu Comminity College)

Planets have elliptical orbits with the sun at one focus orbits are not circles Aristotle's cosmology required circular orbits sun is not the center

Equal areas swept in equal times orbits are not at constant speed Aristotle's cosmology required constant speed

Period squared is proportional to distance cubed called The Harmonic Law period is the time required for one orbit distance refers to the average distance from the sun planets further from the sun move slower Aristotle's cosmology required all planets to move at the same speed the relationship (harmonic ratio) is the same for earth and planets, except the moon table shows relationships

Pictures of the two comets

These photos were taken by John Chumack of Galactic Images

Hyakutake tail

That's about where the similarity ends. Hale-Bopp is a dusty comet, Hyakutake was dust-poor. The nucleus of Hale-Bopp is thought to be huge, about 20-30 kilometers in diameter, while Hyakutake's is small, only about 1-2 kilometers across. Hale-Bopp was discovered a year-and-a-half before closest approach, and has been in our skies for months; Hyakutake appeared virtually "out of nowhere", and the show was over almost before we had time to react. Hale-Bopp must have appeared in our skies 2500 years ago, while Hyakutake last showed up (if at all!) over 50,000 years in the past.

So, why did Hyakutake put on such a great show, when it is merely "peanuts" compared to the current comet? For one thing, Hyakutake came nearly four times closer to the Sun than will Hale-Bopp - 0.23 AU compared with 0.91 AU. For another, we got to see Hyakutake broadside, while Hale-Bopp will be viewed from, at most, an aspect angle of 45 degrees. But most important of all, Hyakutake came close to us - very close - missing the Earth by a mere 0.1 AU - while Hale-Bopp will, at best, be over 9 times further away. So even though it wasn't a "great" comet in its own right, it sure appeared that way to us!

What this all means is that Hale-Bopp won't produce nearly as long of a tail as Hyakutake - which produced a 52 degree-long tail as seen by this observer, with some reports of 70 degrees or longer. Hale-Bopp's tail will probably appear more like 10 degrees long - 20 degrees at most. On the other hand, we expect Hale-Bopp to be bright since it should spew out lots of "stuff" into a smaller region (from our vantage point) of the sky. So even though the total overall brightness may be roughly the same, it should be more concentrated, and hence easier to spot, with Hale-Bopp.

Sodium tail

The picture on the left is the discovery image of the sodium tail in Comet Hale-Bopp taken on the 16th April 1997. The tail appears as a very straight narrow feature extending from the head of the comet to the upper left. The picture on the right is an image of Comet Hale-Bopp showing the ion and dust tails of the comet, taken a few minutes before the discovery of the sodium tail. The dust tail is the broad tail pointing straight upwards, while the ion tail is the filamentary structure to the left. Comparison of the two images shows how the sodium tail has a completely different appearance to the other tails of the comet.

Astronomical Society of the Pacific

Stars with trains of fire. For King Harold and the Saxons, the appearance of a comet in 1066 was a portent of doom; for Duke William and the Normans, the same comet was a blessing from heaven. Later that year, William's army defeated Harold's forces at the Battle of Hastings. William's wife, Queen Matilda, commissioned this tapestry, the famous Bayeux Tapestry, to commemorate her husband's victory. Today we know that the comet was Halley's comet on one of its recurring visits.

Callisto crater chains

A portion of a chain of impact craters on Jupiter's moon Callisto is seen in this image taken by the Galileo spacecraft on November 4, 1996. This crater chain on Callisto is believed to result from the impact of a split object, similar to the fragments of Comet Shoemaker- Levy 9 which smashed into Jupiter's atmosphere in July of 1994. This high- resolution view, taken by Galileo's solid state imaging television camera during its third orbit around Jupiter, is of Callisto's northern hemisphere at 35 degrees north, 46 degrees west, and covers an area of about eight miles (13 kilometers) across. The smallest visible crater is about 140 yards (130 meters) across. The image was taken at a range of 974 miles (1,567 kilometers).

Oort cloud

"Comets are like cats. They have tails and they do precisely what they want." David Levy

Comet cartoon

metshow

small comets NASA's Polar Spacecraft Confirms ... Small Comets are Pelting Earth Part 1 A series of spectacular images produced by state-of-the-art cameras on NASA's Polar spacecraft have confirmed that Earth is being pelted by thousands of small comets each day. These never-before-seen images establish the physical reality of the house-sized "snowballs" that weigh tens of tons, break up as they approach Earth, and deposit large clouds of water vapor in the upper atmosphere.

This image, for example, which was taken on Dec. 31, 1996 by the Low-Resolution Visible Camera aboard the Polar spacecraft, is composed of three consecutive snapshots of a cometary water cloud taken about six seconds a part.

These Earthbound comets, however, represent no threat to either people on the ground or in orbit as these objects disintegrate far above the Earth's atmosphere. "In fact," says Louis A. Frank, the University of Iowa space physicist who first proposed the existence of these small comets more than a decade ago, "this relatively gentle cosmic rain and its possible simple organic compounds may well have nurtured the development of life on our planet."

In the Polar images the atmospheric holes appear as clusters of pixels, or picture elements, rather than as single pixels as in the Dynamics Explorer images, which had much less spatial resolution. The atmospheric holes are measured to be 25-to-50 miles across. The Earth camera on Polar detects these atmospheric holes at a rate that suggests Earth is being bombarded by 5-to-30 small comets per minute, approximately the same frequency recorded by the Dynamics Explorer imager.

A spectacular disruption of a small comet the size of a two-bedroom house took place 5,000 to 15,000 miles above the Atlantic Ocean at 2228 UT on September 26,1996. A view of Earth at the time of the event has been superposed onto the far-ultraviolet image as a frame of reference. This unusually bright and long-lived trail, which was captured by the Earth Camera aboard NASA's Polar spacecraft, ends over Germany. Images like this one show that there is a large population of objects in Earth's vicinity that have not been previously detected.

Chicxulub

Fig.1. Surface geology, ring locations from gravity data, and wells near the Chicxulub impact basin. The three wells that penetrated impact melt rocks and breccias beneath the carbonate cover rocks are C1 (Chicxulub 1), S1 (Sacapuc 1), and Y6 (Yucatan 6). Other well sites shown are Yucatan 1 (Y1), Yucatan 2 (Y2), Yucatan 5A (Y5A), and Ticul 1 (T1). The Yucatan 4 (Y4) well site is located off the map, ~65 km east of Y5A. Carbonate units at the surface are Q (Quaternary; <2 Ma), Tu (Upper Tertiary; ~2–35 Ma), To (Oligocene; ~25–35 Ma),Te (Eocene; ~35–55 Ma), and Tpal (Paleocene; ~55–65.0 Ma). The crater center is indicated by ×. Hatchured lines represent the Ticul fault system. Dashed lines indicate trend of ringlike zone of water-filled sinkholes.