Irene Worthington Baron



Comet ISON is still orbiting the Sun. By 1 June 2013 it will be inside the orbit of Jupiter, meaning it will be closer to the Sun than Jupiter. By the 1 August, it will be halfway between the orbits of Mars and Jupiter. By 1 October, it will pass within 7-million miles of Mars. By 1 November, Comet ISON will be closer to the Sun than Earth. By 11 November, the comet will be closer to the Sun than Venus. By 23 November, it will be closer to the Sun than Mercury. It is at this date that it should be easily seen from Earth. The end of November finds the comet at perihelion, at its closest point to the Sun. As it loops around the Sun, it will begin the outward trip in its orbit back into space. On 26 December it will be at its closest point to Earth.

According to past predictions, those of us in the northern hemisphere should see the comet tail at its largest between 23 November and 14 December, according to predictions. If you have looked at the trajectory of the comet across our skies, it appears to be low on the horizon. For me, that means leaving my backyard viewing site and venturing to a hill top free of trees. There is an excellent viewing site at a local state park where many persons congregate to watch meteor showers.

When persons interested in comets try to find information about ISON, they most likely will ask about emissions of material, such as sublimation of ice to gas. Sublimation is the process of a material like ice turning directly to a gas without going through the water/melt stage, such as the sublimation of frozen carbon-dioxide (dry ice) to gas.

The comet is moving in the vacuum of space. When ice particles within it heat up and expand, the vacuum of space with no pressure allows venting or outbursts. The outbursts are created when the ice begins to sublimate and turn into gas. The increased pressure of the process has nothing to stop expansion. The gases may then stream out into space or occasionally burst into space. It would be interesting to see a video image of a huge outburst on a comet.

The rotation of the comet is also questioned, for the different sides of the comets make for different images when the comet is photographed. I do not have any special photographic equipment except for a couple of great Canon cameras, one digital EOS60, but am interested in seeing the infrared imaging of ISON. Other items of interest that may be used to compare ISON with other comets are:

1. Nearby fragments orbiting with the comet

2. Volatile materials which expand with heat from the Sun (water, snow, ice)

3. Spectral images of the dust to examine what elements are present in the reflective light

4. Infrared images to see the differing temperature areas as they change

5. Tail of the comet changes with length, width, and shape

6. Atmosphere surrounding the head of the comet which continually changes due to escaping gas

7. Images via x-ray, ultraviolet, infrared, hydrogen, etc.

8. Dust to gas ratio changes which may be rapid

9. Dust molecules (mixtures of Hydrogen, Carbon, Nitrogen, Oxygen and Sulfur, Magnesium, Silicon, Iron, Nickel, Chromium, etc) and their production rates as they change daily

10. Albedo compared to other comets (albedo: percent of light comet reflects)

11. Outbursts of material caught on film

12. Changes observed as it passes close to the Sun.

This is a NASA link to an Applet animation of Comet ISON. It shows the orbits of the planets and the orbit of Comet ISON. The planets are white lines and the comet a blue line. The Orbit Viewer applet was originally written and provided to NASA and interested comet fans by Osamu Ajiki of AstroArts and further modified by Ron Bealke of JPL. This link is one easily used by most anyone, even children. Check it out at:;orb=1;cov=0;log=0;cad=0#orb

Since the comet is coming soon, it would be a good idea to educate your family members and friends as to expectations. I have had adults tell me they hid under their bed when the media reported a comet was visible in the sky. Reassure others that the comet is not going to hurt them.

Eventually we may go through the orbit of the comet, such as when we go through the orbit of Comet ISON in January 2014. When we do pass through a comet orbit, any fragments left behind in its orbit may be seen as they pass through our atmosphere as a meteor. If a meteor would hit Earth, it would be called a meteorite. The only difference in the name is the location. When the rock fragments remain in space and do not approach Earth, they are called meteoroids. When we have meteor showers on Earth, a display of "shooting stars," we are usually passing through the orbit of a comet.

If Earth passes through the orbit of a comet, does that mean we may collide one day? It’s probable. However their orbits are usually so large, it doesn’t happen very often. I’m sure some of the craters found on earth may have been from comet debris or small comets. ISON is only a few miles in diameter. Is that dangerous? Any collision is dangerous. Basic information about comet impacts can be found at:

In our recent past, many witnessed comet fragments hitting Jupiter. That experience brought home the fact that Earth could be impacted by comets. Links to view the Jupiter impacts include:

The Discovery Channel (excellent video):


Here in Ohio is a state park called Serpent Mound. At that impact site, ancient Indians built an earth mound to show what hit the area to cause the damage. The impact crater is about 7-miles in diameter. The image shown here looks like a snake holding a ball. Astronomers suggest it is the head of the comet with the comet tail behind it. Links to information concerning that impact site include:

Ohio Historical Society:

Arc of Appalachia Preserve System:

The Metropolitan Museum of Art:

As Comet ISON approaches, more information will be available throughout the Internet, astronomy magazines and other media. Since this comet is predicted to be the largest one to ever pass Earth, I hope it is spectacular. Keep looking up!

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