Friday, January 19, 2007

Horizons, Part 2

Ok, so, now you've figured out how to connect to the Horizons database. What do you do from there? Well, there are several things to do once you connect. The first thing you do is search for what you want. For example, lets pick poor old Pluto. Now, type pluto into the prompt line.

Horizons> pluto
Press enter. You should now get this:

Multiple major-bodies match string "PLUTO*"

ID# Name Designation IAU/aliases/other
------- ---------------------------------- ----------- -------------------
9 Pluto Barycenter
999 Pluto 134340

Number of matches = 2. Use ID# to make unique selection.
Select ... [F]tp, [M]ail, [R]edisplay, ?, :

This is something that is peculiar to this database, especially with planets and dwarf planets. The first entry is the barycenter, which only has meaning if the (dwarf) planet has moons. The barycenter is basically the point where the (dwarf) planet and the moon revolve around. The (eight) planets are so heavy, that the barycenter actually lies INSIDE the surface of the planet. So, there usually isn't that much of a difference. This probably has a use for scientists who need to know the barycenter of planets to launch probes or stuff, but for us, we just want "#999 Pluto". So, type in the number "999" (without quotes) and press Enter. You should get this next:

Select ... [F]tp, [M]ail, [R]edisplay, ?, : 999
Revised: Mar 24, 2005 134340 Pluto 999

Solution update to support Charon's 2005-Jul-11 occultation of 15th magnitude
star UCAC2 26257135. Fit to all available observations.

PHYSICAL DATA (updated 2006-Feb-27):
Mass Pluto (10^22 kg) = 1.314+-0.018 Density Pluto:
GM (planet) km^3/s^2 = 870 (R = 1137+-8 km) = 2.06 g/cm^3
Mass ratio (Mc/Mp) = 0.12 Radius of Pluto, Rp = 1151 km
Surface gravity = 65.5 cm/s^2 Geometric albedo = 0.3
Sidereal orbit period = 247.92065 yr Orbit velocity = 4.749 km/s
Escape velocity (km/s)= 1.3
Select ... [E]phemeris, [F]tp, [M]ail, [R]edisplay, ?, :

Now you have a whole bunch of data on Pluto. Now you can select one of several options. You enter "e" to get ephemeris, which are basically coordinates for where Pluto is. Getting these are a long arduous process that I'm not going to elaborate on now, probably because I have no clue how this works either. Now, you can enter "f" to store the data temporarily to retrieve it later from an ftp server (which I don't think you have much of a need for). Press "m" to e-mail the data to someone (or yourself). And press "r" to redisplay the data. When you're finished and want to search for something else, just press Enter and you'll be able to enter in another object.

Now, these are only a few options you can use. For other objects, you get other options. One thing to remember is, whenever you need help, just type "?". If that's not enough, then type "?!" for more details. Now, there's my summary on the Horizons service. Hope you all enjoyed it.

1 comment:

Science Thinker said...

so i can use this to find info on any star/object that i choose? thanks!