Close Miss This Morning 2021 OD1

[bigmasterdrago]

Had an unseeable this morning pass just 255,386Km out at possibly 15-16 mag. Was slightly below my horizon and after daylight so not even a possible witness. The discovery observations had it near opposition moving from north to south but inside lunar orbit so great phase angle. Moving quickly into southern hemisphere at 4'/m to 6'/m. A real screamer - Pegasus to Grus - 70° in 24 hours. Not a big rock at possibly 13 meters. When it was in a dark sky, too faint and moon. But cool to track anyway. Good practice.

[PMSchu]

Hi BMD,

For some reason 2021 OD1 wasn't in my MP DB as of yesterday. I did have 2021 OY. Had to do a special download of 2021 OZ from the MPC to get that one as it wasn't downloaded with the NEOs at Today's Epoch.

It went right past the Helix Nebula ~0300 EDT. Just detectable in the 13".

Phil S.

[bigmasterdrago]

Wasn't sure which rock went past Helix. Funny as OZ and OY pass just 14° apart in a few hours but OZ is 5,498,000Km away while OY is 3,972,000Km away

[PMSchu]

It was 2021 OD1 this AM that passed Helix.

Phil S.

[bigmasterdrago]

I just re-ran the ephem for 2021 OY & 2021 OZ. They appear in my sky to be visually separated by 12° while up 37° and 49° respectively at 05:18 CDT 8/1/2021. The difference in their distance from me is 1,366,26Km with OZ being the farther away but the brighter @16.4mag. Both have a phase angle of ~90°. This shows how different the rocks are - OZ is much larger at 62-140 meters! At the noted time, both are moving across my line of vision ~22.5"/minute. Fun stuff and nice to have software making this an adventure.

[PMSchu]

Hi BMD,

2021 OD1 was a perfect candidate: very fast & bright enough to be observable from 30°N. For some reason it wasn't in my download of NEOs at Today's Epoch done on 29 July.There were many after 2021 OD1 up to 2021 OY.

Frustrating, they aren't that frequent. Hated to miss this one.

Phil S.

[bigmasterdrago]

So, so often we see this discovery and string of observation AFTER the closest approach. And even if we get a bit of warning (day or two), the arc is so short that getting a good set of elements is tricky. And with the gravitational perturbations of both the Earth & Moon, tracking and locating get real tricky for software that will need a close set of osculating elements. But I'm sure liking the chart output in ST4. It's fun working the problems out and using all the tools we have at our disposal. It becomes time critical and sharing an ephemeris is impossible due to the parallax from different locations. And then most are at our visual limit or beyond. Still fun!

[PMSchu]

Accprding to the CNEOS website there are 3 more close approaches of 2021 OA1, OB1 & OE1. These weren't part of the NEOs at Today's Epoch of 2021 Jul 29. I'll see what they look like.

Phil S.

[bigmasterdrago]

I think I ran those as a practice run and all were ~faint 18th mag. at closest to me. 2021 NY1 jumped out at me due to its size and 4LD pass distance but it looks to be daylight when close and 15th mag. Too faint still for me. Keep looking up.