# head of NASA’s ISON Observing Campaign

Astronomy.

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in by | Comet ISON News Links.
October 1, 2013 in by | 2 comments “The Life and Death of Comet ISON”  — Will comet ISON die on Nov 28.
(Discover Magazine).
NASA Comet ISON Toolkit.

## Could Comet ISON Still Become the ‘Comet of the Century? (space.com)

### Potentially Dazzling Comet ISON: 8 Essential Facts (space.com)

#### Comet ISON: A Viewing Guide from Now to Perihelion (universetoday.com)

Comet ISON passing Mars today.
October 1, 2013 in by | Permalink Comet ISON will pass Mars at around 1600 GMT (noon in the eastern USA) today at a distance of about 7 million miles.
Unfortunately.

#### It is right beside the moon this morning in Leo

so it would be quite difficult to see even with a telescope.
(The moon will be out-of-the-way after Oct 5).
I made a video and a Mathematica demonstration showing the path of ISON through the solar system, but there is a much nicer interactive viewer at solarsystemscope.com.
Comet ISON, Perihelion, Mars, and the rule of 13.3.
September 9, 2013 in by | 2 comments Comet ISON passing Mars Comet Ison passing Mars (Wolfram Alpha) I just got back from the Black Forest Star Party where Dr.
Carey Lisse, head of NASA’s ISON Observing Campaign, gave a speech on comet ISON.
Comet ISON (see [1], [2]) is passing by Mars soon (Oct 1) and it will be “grazing the sun” before the end of the year, so I wondered if there was some relationship between the orbital period of a planet and the time it takes a passing comet to go from the planet to the Sun.
Turns out there is a relationship.
Here’s the approximate rule: Time to sun $\approx$ Orbital Period / $3 \pi \sqrt{2} \approx$  Orbital Period / 13.3.
In the case of ISON and Mars, Time to sun $\approx$ 687 days / 13.3 $\approx$ 52 days.
But Oct 1 + 52 days is Nov 22, and perihelion is on Nov 28.
Why so far off.
Well, .

#### Turns out that Mars is farther from the sun than usual

If we correct for that, then the formula estimates perihelion to within 1 day—much better.
For those that like derivations, here is the derivation for the 13.3 rule.
The orbital period of a planet is $T_p = 2 \pi \sqrt{ r^3 \over {G m_S} }$ where $m_S$ is the mass of the Sun, $r$ is the radius of the planet’s orbit (or, more precisely, the semi-major axis of its orbit), and G = 6.67e-11 is the gravitational constant.

#### The speed of a comet from the Oort cloud is derived from its energy

Kinetic Energy = -Potential Energy $\frac12 m v^2 = G m m_S / r$ $v = \sqrt{ {2 G m_S}\over{r}}$ where $r$ is the distance from the comet to the sun.
So the time for a Sun grazer to go from distance $r_0$ to the sun is about $$T_S = \int_0^{r_0} {1\over v} dr$$ $$= \int_0^{r_0} \sqrt{ r\over{2 G m_S}} dr$$ $$= \frac13 \sqrt{ 2 r^3 \over{G m_S} }.$$ Finally, $$T_p/T_S = {{2 \pi \sqrt{ r^3 \over {G m_S} }}\over{ \frac13 \sqrt{ 2 r^3 \over{G m_S} }}} = 3 \pi \sqrt{2} \approx 13.3.$$ A New Dalton Minimum.
(Off topic).
April 2, 2013 in by | 1 comment Seemingly weak Solar Cycle #24 A long time ago I was a meteorologist at the Joint Typhoon Warning Center in Guam.
One of my forecasters had a friend that used solar images to forecast wheat futures.
I wonder what those people are predicting these days.

#### The Dalton minimum occurred between 1790 to 1830

If the sun does not perk up, .

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