MadSci Network: Astronomy
Query:

Re: In which conste;llation could you find the minor planet 719 Albert?

Date: Thu Jun 14 00:21:31 2001
Posted By: Paul Filmer, Staff, Geosciences Directorate, National Science Foundation
Area of science: Astronomy
ID: 992197453.As
Message:

Question: In which constellation could you find the minor planet 719 
Albert?

Well, since Albert is really zipping along, it depends when you look. This 
summer it will actually be in a pretty good position for observers in the 
Northern hemisphere – but even though it will pass pretty close to Earth, 
it’s pretty small (between 3 and 6 km radius) so it will be very dim and 
only observable through a large telescope.

Today, June 13 2001, Albert is in Delphinus, but by tomorrow it will have 
moved into Equuleus. Albert moves on into Pegasus by June 18, where on 
July 31 it will reach its highest point in the sky. Albert will move into 
Andromeda by August 8, where it then starts to go into retrograde motion 
as the Earth overtakes it (where it looks like it’s moving backwards, like 
a car you are overtaking, even though both of you are still moving 
forwards). By August 18 it will cross into Pisces, and by September 1 it 
is in Aries, where on the 5th it will reach its closest approach to Earth, 
about 43 million kilometers.

OK. Tell me more. Albert has an interesting history. The number 
(719) refers to the fact that it was number 719 in a list of asteroids 
that astronomers started making over two hundred years ago. It was 
discovered in 1911 by an Austrian, Johann Palisa, who was working in 
Vienna, and it was also seen by a Danish observer within a few days after. 
But then they lost it!

How can you lose an asteroid? Aren’t these things big? Umm, well, 
yes, but space is even bigger, and there’s a lot of it out there. Even 
something as big as 6 km across looks pretty small when it is several tens 
of million of kilometers away! Also, we need to observe objects several 
times (and be sure we are actually seeing the same one) to be able to 
figure out their orbit – and the two times Albert was seen in 1911 were 
not enough to give us a good estimate of the real orbit. In fact, the next 
time we looked for it, we were off by several degrees, which, when you 
look though a big telescope, is a HUGE error.

So, how did we find it again? An astronomer in Arizona called 
Jeffrey Larsen observed an object on May 1, 2000 that he called 2000 JW8, 
which was tracked by Larsen and several others for several days to better 
determine its orbit. By May 9, Gareth Williams of the Minor Planet Center 
was able to determine that 2000 JW8 was in fact the long-lost Albert. (You 
can run the 2000 JW8 orbit “backwards” and tell that it was in the right 
place in 1911).

So how do you know where it is now? To tell where any orbiting 
object is, you need seven pieces of information. The best way to think of 
it is as follows: you need three to tell you where it is (x, y, z) and 
three more to tell you how fast it is moving (Vx, Vy, Vz), and one more to 
tell you what time it was when you took these measurements (t). In real 
life, measuring orbits using x, y and z is REALLY HARD, so astronomers use 
another set of seven measurements that sound really strange (see below), 
but they are essentially giving us the same information. Then you use the 
laws of physics to tell you how the object will move either in the future 
or the past. It turns out that Albert orbits between the Earth and 
Jupiter, and will come ‘close’ to both planets on this time round the Sun. 
Albert takes about 4.28 years to orbit once, and comes close to Earth 
almost exactly every 30 years (...1911, 1941, 1971, 2001...).

I’m game – gimme the full set of numbers in all their gory detail 
OK, here goes. These are also called the “Orbital Elements.” You can use 
these in a lot of astronomy software for computers to see pretty much 
where Albert will be anytime. That’s how I figured out where it was over 
this summer – I just plugged these elements into a pretty simple astronomy 
program on my Mac and presto!

Semi-major axis (a):  2.636667 a.u.
Eccentricity (e): 0.548273
Inclination (i):11.3095
Longitude of Ascending Node: 184.9305 (Epoch 2000.0)
Longitude of Perihelion:154.2885
Epoch (T): 2001 August 21.2582
Mean Motion (n): 0.2302084

Here are two good articles on 719 Albert that cover its history and 
rediscovery: http://cfa-
www.harvard.edu/cfa/ps/pressinfo/Albert.html http://neo.jpl.nasa.gov/ne
ws/news102.html

And here is the technical bulletin that gives the gory details: http://cfa-
www.harvard.edu/iauc/07400/07420.html

An interesting website is the Spacewatch project of the Lunar and 
Planetary Observatory of the University of Arizona, who watch for 
asteroids all the way out to the orbit of Neptune: http://www.lpl.arizona.edu/sp
acewatch/

Hope this helps you Sam!


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