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Comet Hyakutake (1996 B2)



At long last we again have a comet to be excited about: Hyakutake (1996 B2). (And possibly Hale-Bopp, and another Hale-Bopp site, within a year!)

One fact that makes Hyakutake so exciting is that it will pass within ten million miles of the Earth! On the day of closest approach, March 25, it will move across 17 degrees of sky. Hyakutake is an infrequent visitor with an orbital period currently estimated at 16,400 years.

The next couple of weeks should give us a great show, the skies willing. With the aid of The Starry Night I have tried to produce some graphics of interest and usefulness for observing and understanding Hyakutake.
One big trick to observing possibly faint objects, such as Hyakutake's talk, is to use "averted vision": not looking directly at something, but rather slightly to the side (or above/below) of it. "There are two kinds of light sensitive cells in the retina, rods and cones. The cones give us the highest definition and also provide color vision while the rods are very much more light sensitive. Most of the retina has a mixture of the two types of cells but in the center are only cones. We naturally use this high definition region for reading and other detailed work. Averted vision causes the image (in this case, of the comet) to fall on the more sensitive rods." (Thanks to Kevin Patfield for the writeup.)

For organized Chicago area viewing, there are events:
near Palatine and at Adler Planetarium

Also, Adler Planetarium has a new sky show: Comets are Coming

If you can, I really urge you to get out to a "dark sky" site (away from our light-polluted cities) and get a true look at this comet. (No, I have not had the pleasure yet. Sigh.) While you are there, take a moment to look around the rest of the sky. You will be surprised at what we lose thanks to our wasteful ways:

Robert's Observations and What to Expect

Friday March 15th:
I was finally able to observe the comet from Chicago skies (limiting magnitude about 4 that night). If you knew right where to look, you could tell that something was there. The comet was trivial to observe in low-power binoculars, with a slight hint of a tail.

Thursday March 21st:
The afternoon sky was wonderfully clear, but unfortunately some scattered clouds and haze moved in for the evening. Even so, the comet was a very obvious object in the eastern sky while standing in a parking lot. Relocation to a slightly better site (but still Chicago skies) showed a one-degree wide coma (comet nucleus plus gas shell) quite well with elongation (hint of a tail) towards two o'clock.

For those who would like a realistic idea of what to expect, I have attempted to sketch what the naked-eye comet looked like tonight. The comet is the oblong blob towards the bottom of the graphic. Arcturus is the bright star towards the top. (Arcturus' size is exaggerated for viewing purposes. The comet is ten degrees below Arcturus, and I sized the comet's appearance to match that scale.)

Friday March 22nd:
I made it to an almost dark sky site (limiting magnitude 5.5 straight up, 4 closer to the horizon) a few miles south of Joliet. Tonight, the comet would be near Izar, with any tail pointing back towards Arcturus. The comet really had moved in the sky since the previous night. In fact, the comet's motion over the course of a couple hours was easily noticable.

While the comet was visible to the naked eye in Evanston, no tail was visible (even with binoculars), just a slight elongation. At the darker site, the comet was easily visible to the naked eye. In addition, a five degree tail was initially visible with averted vision. After dark adaptation, a fuller tail was visible, extending about fourteen degrees(!), passing just above Arcturus, ending near Muphrid.

Again, I have made an image of my observations. The top frame shows what the view was like from Evanston, the bottom frame is the view that the semi-dark sky site provided.

Monday March 25th:
By the time I was ready to go to bed the skies had finally cleared. Grabbing my binocs, I went downstairs. From the front of the apartment building the comet was quite visible. A tail of at least seven degrees was visible in my binoculars.

Tuesday March 26th:
Hyakutake was near Polaris (the North Star) tonight (about 3.5 degrees away). The nucleus is not as distinctly visible as it was previously (more active closer to the Sun? longer line of sight through the coma now?). With averted naked-eye vision, a tail of about 7-8 degrees is now available even with the city sky.

(Due to differences in monitors, comet images will be slightly brighter or darker on your monitor than what I intended, though the general idea will still be communicated.)

Hyakutake's Path Through the (Chicago) Sky

(The general location in the sky should be valid for any site.)

I have put together an animation of Hyakutake's path through the Chicago night sky from Marth 15th through April 15th. The green line is the comet's path on the sky since March 15th. The yellow, connect-the-dots lines are the constellations.

Hyakutake on the sky: AVI (695kb)
Hyakutake on the sky: QuickTime (750kb)

You can also view individual frames for specific dates.

(Need QuickTime? Check out Cross-platform QuickTime.)

The label in the upper left gives the local (Chicago) time and location in the sky, for that particular view.

The Comet Hyakutake Diary from Abrams Planetarium provides excellent written descriptions on finding the comet.

The comet and stars will move together across the sky during the night as the Earth rotates. Additionally, around the time of closest approach (March 25th), the comet will show motion against the background stars over the course of just a single night. Because of this motion you should just utilize the images here as a guide for where in the sky to start looking, with the emphasis on the constellation background. Finding the comet from March 20th-28th should not be difficult due to its brightness.

Hyakutake's Path Through the Solar System

The orbits of the planets about the Sun all lie in roughly the same plane; the plane of the Earth's orbit has a special designation: the Ecliptic.

The orbit of Hyakutake (purple) lies in a plane nearly perpendicular to the Ecliptic (green). (The bright star is the Sun.)

A picture of the comet's path (purple) through the inner solar system shows that it came up through the ecliptic between the orbits of Mars (red) and Earth (green).

(The comet's path will of course be a smooth parabola, rather than a sequence of straight lines.)

After passing near Earth on March 25th, the comet will then pass by the Sun on May 1 and swing back down through the Ecliptic, after which it will no longer be viewable from the Northern Hemisphere.

I have prepared two animations of Hyakutake's voyage through the inner solar system from the comet's viewpoint.

In the first animation we ride the comet from March 18th through May 13th while watching the Earth.
Hyakutake in the inner solar system: AVI (525kb)
Hyakutake in the inner solar system: QuickTime (670kb)

The second animation shows the comet's voyage starting from October 21, 1995 through early summer 1996 with the focus on the Sun.
Hyakutake through the solar system: AVI (4Mb)
Hyakutake through the solar system: QuickTime (3.4Mb)

(Need QuickTime? Check out Cross-platform QuickTime.)

Further exploration

For further exploration, you can visit one of many Comet Hyakutake (1996 B2) web pages:
A quite good article from the Chicago Tribune.
Hyakutake at JPL.
Night of the Comet!
Comet Photography for Everyone
Hyakutake from University of Washington
The March, 1996 Appearance of Comet Hyakutake
What is a Comet? and The Motion of Comets from the Comet Shoemaker-Levy 9 Educator's Guide
Comet Introduction from Views of the Solar System

You may also want to explore the virtual night sky yourself:
The Starry Night (Macintosh) (Check out the balloon help!)
Skymap (Windows) (Orbital elements for comets.)

(For Northwestern University users I have provided a local mirror of the installation files.)

Netscape HTML Checked! March 26, 1996 - Robert Lentz (

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