Each month I will describe sights of interest in the night skies of South Carolina. These sights will be broken down into three sections: what you can see with the naked eye, with binoculars, and with a small telescope. The best time to view the night sky is at and around the times when the Moon is not visible, what is known as a New Moon; which will occur this month on November 3rd. For November, your best viewing nights will be from November 1st to the 7th, and November 23rd to the 30th. The Star chart below is set for Florence, SC on November 15th at 9 pm.
Astronomy magazines, planetariums, and all the news media will be heavily focused on the approach of Comet ISON late this month. As the comet comes closer, astronomers may also be able to predict by mid-month if Comet ISON will be spectacular, or unimpressive. However, these early predictions may not hold true because the comet will make a rare close encounter as it swings around the Sun; called perihelion. At perihelion, the combination of the intense heat of the Sun, and the intense gravitational forces involved may result in an impressive flare up of the comet, or it tear the comet apart, or no effect. The bottom line is that we will have to have our Thanksgiving turkey before we find out the true nature of Comet ISON.
Many people do not get up before sunrise which does not fit well for viewing Comet ISON. You will notice in the comet orbit image below that ISON’s arrival and exit from the Sun occurs in front of the path of the Earth.
Therefore, the best views will be on the morning side versus the evening side of the Earth. The good news is that at and near perihelion, ISON will be so close to the Sun, it should be visible before sunrise and after sunset. This sets up the following scenario: Best view of ISON; Morning, Nov 20th to the 27th. Morning and evening, Nov 30th to Dec 1st. Morning, Dec 2nd to Dec 10th. If ISON does turn out to be a brilliant comet, it should be visible before Nov, 20th, and after Dec. 10th.
Last March I discussed the arrival of Comet Pan-STARRS, which was not bright at all. In that column I also gave a general overview of comets. With the awaited arrival of Comet ISON, I am repeating some of the comet overview from the March column.
A comet is often described as a giant frozen snowball several miles across, containing water, gases and rocks. It is believed that comets are objects leftover after the formation of our solar system, and reside in an area orbiting the Sun beyond the dwarf planet Pluto. This area contains two regions known as the Kuiper Belt and the Oort cloud, shown below.
Note, the symbols AU on this image mean astronomical units. One AU is the distance from the Earth to the Sun; 93 million miles. Therefore, the Oort Cloud is 93,000,000 X 55,000 miles away!
The Kuiper Belt is like the asteroid belt in that it lies in the plane of the planets in our solar system. It is unlike the asteroid belt because it contains mainly snowball-like objects, and not rocky asteroids. It also contains three dwarf planets; Pluto, Haumea, and Makemake.
The above image does not give an accurate representation of the Oort Cloud. The Oort Cloud is not a belt of objects, but a sphere. A better image is as shown below.
If a comet’s orbit is near the plane of our solar system, then it is likely that it originated from the Kuiper Belt. If a comet’s orbit is well out of the plane of the solar system, then it originated from the Oort Cloud. Comet ISON’s out of plane orbit implies that it came from the Oort Cloud.
Let’s return to the origin of the comets. As leftovers from the formation of our solar system, comets always resided in this distant place never feeling the heat of the Sun. Periodically, some unknown object hits or disturbs their orbit, and they “fall” toward the Sun. As they hurdle past the orbit of Jupiter, for the first time in 3-4 billion years they feel; heat! Once exposed to heat, comets now start to boil away gases such as carbon dioxide. As the journey toward the Sun continues additional gases and then water-ice starts to boil off. Actually the ice does not boil away; instead it is converted directly from solid ice into gas, a process known as sublimation. As this sublimation continues, solid debris imbedded in the ice begins to crumble off, and once the comet passes by the Earth’s orbit, and nears its closest approach to the Sun, called perihelion, the comet has now reached its most unstable state. The heat and energy of the Sun can tear the comet apart, but the most impressive effect is the comet can form a huge trail of rock, ice and gases millions of mile long; which we call the comet’s tail. An interesting property of the tail is that it always points away from the Sun. Outer space is devoid of almost all matter, so as the comet moves in its orbit, there is no friction from space itself, so the force of the solar wind can easily blow the comet’s debris away from the Sun.
Below is a computer generated image of the best possible ISON scenario looking west from ScienceSouth on November 30th.
Naked Eye Sights: Comet ISON, we hope, beginning about November 20th in the east before sunrise. At the end of the month it should be visible both at sunrise and at sunset, and then in early December visible only before sunrise.
Binocular Sights (7 to 10 power): Comet ISON
Telescope Sights (60-100mm): Comet ISON, best viewed at wide field and at low power through a reflecting telescope.
Happy Thanksgiving! See you next month.