**** Edit, appearently, Latex is not working right now. Here's my best effort to duplicate this post without Latex: ***(adsbygoogle = window.adsbygoogle || []).push({});

In the following journal paper:

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1995AJ....110..420M&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf [Broken]

the top of page 424 contains this formula

a(t)=a_{f}-delta a exp(-t/tau)

which if I'm not mistaken is the same as

a(t)=a_{f}-delta a e^{(-t/tau)}

It gives an object's semi-major axis at time t for an object that is migrating from the orbit where it formed, to where it is in the current epoch.

tau is the timescale of the migration

and a_{i}can be computed by

a_{f}-delta a

It would make sense to me that a(0) should equal a_{i}, and a(tau) should equal a_{f}.

My first assumption is correct. a(0) does equal a_{i}since e^{0}=1.

But my second assumption can only work if e^{-1}= 0, which it does not.

Does anyone care to guess what I'm doing wrong?

*** The Latex version for when TEX starts working again ***

In the following journal paper:

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1995AJ....110..420M&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf [Broken]

the top of page 424 contains this formula

[tex]a(t)=a_{f}-\delta a exp(-t/\tau)[/tex]

which if I'm not mistaken is the same as

[tex]a(t)=a_{f}-\delta a e^{(-t/\tau)}[/tex]

It gives an object's semi-major axis at time t for an object that is migrating from the orbit where it formed, to where it is in the current epoch.

[tex]\tau[/tex] is the timescale of the migration

and a_{i}can be computed by

[tex]a_{f}-\delta a[/tex]

It would make sense to me that a(0) should equal a_{i}, and [tex]a(\tau)[/tex] should equal a_{f}.

My first assumption is correct. a(0) does equal a_{i}since e^{0}=1.

But my second assumption can only work if e^{-1}= 0, which it does not.

Does anyone care to guess what I'm doing wrong?

**Physics Forums - The Fusion of Science and Community**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Help me understand this equation

Loading...

Similar Threads - Help understand equation | Date |
---|---|

B Help me understand light traveling through vast distances in space | Jul 28, 2017 |

I require help with understanding beginner astronomy questions. | Oct 18, 2014 |

After help understanding black drop effect | May 22, 2013 |

Astronomy paper help - professor doesn't understand my wording | Feb 28, 2013 |

Help understanding the Tillotson equation of state | Sep 26, 2011 |

**Physics Forums - The Fusion of Science and Community**