Astronomy

[eak227]

Hey guys, I'm not really sure how useful this will be for Div C astronomy, but I was at a lecture yesterday from someone who helped create this.

Check out theWorldwide Telescope. Give it a shot and let me know how useful it is for DSOs and stuff. Even if it's not good for the event, if you really love Astronomy, you'll definitely appreciate this.

[walkingstyx]

I find a laptop is safer for regionals and similar low-level competitions because those tests don't always stick to the rules and tend to take stars that aren't on the syllabus but showed up in various material that they have bought or been given, stars that you didn't bother to research because they had no right to be there, but are labelled in the alt-texts of pictures on common resources. Our last invitational had a few inappropriate stars that we only found by comprehensively search our laptop for the choices. Having a laptop is safer at small competitions, but, as the same man wrote the rules and the national test, a binder is equally good or better for nationals.

[tad_k_22]

woman*

[binary010101]

Is there anything for the math portion?

[Glacierguy1]

Could someone post a link about how to make an O-C diagram, because every time I search for one I get a link to the Orange County webpage.

[Sheogorath]

I've been looking for a lab on how to make them. But just to help you they're called Observed Minus Calculated Charts.

Post a link if you find anything.

[binary010101]

Can you post a link for the logarithmic formulas?

[Glacierguy1]

http://daniel.eastern.edu/depts/physsci/ephemerides.doc

This may help, but if it does, it's way over my head

[binary010101]

Thanks.

[eak227]

O-C Diagrams
One very useful tool for finding period changes is to compute what is called "O-C" ("O minus C") diagrams. It is based on the following idea: if a star is perfectly periodic, then every period is exactly the same. In that case, we can predict its cycles in advance. If one maximum occurs on, say JD 2450000, and the period is precisely 332 days (and never changes!), then the next maximum will occur on JD 2450332. Then we can compare our predictions with future observations. By observing the star, we can calculate the observed time of maximum and compare it with our predicted time of maximum by simply taking the difference between the observed and computed times of maxima. These are the "O-C" or "observed minus computed" values. After you have determined the O-C values, you can plot O-C as a function of cycle number.

When the O-C values lie on a straight line which is horizontal, the system is periodic and agrees with the calculated value of the period. If the O-C values lie on a straight line that is not horizontal, the system is periodic but the estimated period is not correct and the slope of this line is the difference between the true and estimated periods. When the O-C values change from one straight line to another which has a different slope, the period has changed and the slope of each line is the difference between its period and the estimated period. Finally, when the O-C values do not follow a straight line, the system is not perfectly periodic. Credit: Hands-On Astrophysics, Chapter 13

Taken fromAAVSO

Here is another source saying generally the same thing.