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2010 CA261 Close approach
Hi All,

This is a weird object that I found using the DBPS after updating the MPC elements for NEAs at Today's Epoch today. It's very bright & now moving retrograde WRT earth at 0.03 AU. The mag is currently 10.8, but ST4v estimates it will brighten to 9.5 mag between Sep 3-10 as we overtake it. It's not moving very fast & its orbit is close to earth's.

Might be worth a look if anyone's interested. I'm surprised it didn't appear in previous DBPS searches. It's also not listed on the CNEOS page at JPL.

Good hunting,

Phil S.
In the databases I searched (Horizons and, it has an H of 99.99 with Horizons listing its magnitude over the next 27 days as 93! No decimal point! If you edit the rock, what H does it show? I'm showing 16.6, not 100.

Is it a captured asteroid or an earth orbiting satellite? Unable to find much on it but when importing from the MPC, shows an H=16.5 vs Horizons H=99.99. I've done several searches for it and have come up empty.

In order to get the magnitude tonight and tomorrow morning to be 10.7, I have to change the H to 18.0

I was attempting to run an ephem for tonight and get this - an 8 hour run starting at 22:00 tonight. Should be up ~11 at 10PM but does not show the position. Yes, there is moonlight them but it 10.7 mag, well withing reach of the 13 incher. And I ran the ephem for the 24.


Here are the elements that I downloaded from MPC (NEAs at Today's Epoch on Aug 11): [attachment=1979]

Here's the ephemeris calculated for those elements at the Texas Star Party (TSP) location (the closest site I have that's near you): [attachment=1980]

Finally, here's the trail of 2010 CA261 in the IA at the TSP: [attachment=1981]

It's in retrograde motion & really shows the wiggles caused by the earth's rotation. If you can't see it with a 13", something's wrong with the predicted positions. The eccentricity is very low for this MP, but the inclination is 0.327 - pretty high.

I'll try to image it with one of the iTelescopes. So far that hasn't worked very well for me.

Phil S.
I've made finder charts and ephemerides for tonight from midnight til 6am for our local clubs that agree with those from Horizons. There appear to be only 10 observations of this "rock" in 2010. Also some notes that it could be space junk, a rocket body or an artificial satellite. I'm planning to search the FOV with the 13" in the morning as it is high in the south ~4am. My elements are for 4am on Aug 15th so slightly different.

I've attached a file of elements for 2010 CA261 for the next 10 days from HORIZONS. The time interval is 6 hours.

Hope this helps,

Phil S.
Thanks Phil. Appreciate that. drako
Have to attempt another night as we are totally clouded in SE Texas.

I took 6 30 sec images on iTelescope T16 (150mm refractor) last night. Initial examination of the images didn't show anything that looks like an 11th mag MP. I'm trying to get the images to plot in ST4v, but I didn't request that the images be plate solved. Now I'm playing with Astrometrica to see if that will give the location of the image centers. I seem to be going backwards at present.

According to the Exposure Calculator in ST4i a mag 10.7 object should be easily detectable with 30 sec exposure on this scope: [attachment=1983]

The .FITS image is 65 MB (too big to post here).

At least I'm learning new stuff,

Phil S.
Fun stuff! If you're not in a hurry, an online fits converter is at I've used it a few times. They really compress it small, about 1/10th size but you lose a lot of contrast range. You can also get Fits Liberator and convert to a TIF and then use something else to convert to a jpeg. Keeps a quality image at least. It will still be large but at least manageable and can be uploaded to Dropbox or something.
Did you get it plate solved? I think that will do it for you.

Since Horizons has the H=99.99 as does Lowell but when doing the single minor planet download in ST, it seems to be 16.60, I thought I would experiment. Horizons does not have "Close Approach Data" for 2010 CA261 and has a "Condition Code" = 9 (highly uncertain orbit). So I played around. Looks as if from my location, the rock is close (0.026AU or 10LD) and well placed (180az, 49° up @2:27CDT) in the early morning hours (5-9 UT) on Sept. 1. It's 98% illuminated and the Moon is under 10° up in the ENE. Similar conditions the last few days of August but slightly more Moon interference. Run it for your location.

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