2002 NY 40 Flyby

by Philip C. Steffey

The small asteroid was observed visually, in exceptionally clear skies, with an 8-inch reflecting telescope, on August 16-17 and 17-18 (when it was nearest--about 350,000 miles). But a good deal of preparation was necessary, beginning in early August with computation of the expected celestial path for observation from near my home in Daytona Beach. This was achieved using the online Ephemeris Generator provided by the Minor Planet Center, which was accessed via the Jet Propulsion Laboratory’s homepage on the Internet. Equatorial coordinates at half-hour intervals from dusk to dawn, were obtained for Aug. 15-16, 16-17 and 17-18, when the asteroid was predicted to be at bright 12th, bright 11th, and mid 9th magnitude respectively, and excellently located for my observing site. Considering also the rate of motion relative to the stars, which would reach 1° per hour on the 16-17th and 8° per hour during nearest approach to Earth, charts much more detailed than in popular atlases would be required for efficient visual acquisition and tracking.

Using the AAVSO Variable Star Atlas, I found that the asteroid’s path would take it fairly near several variables, some familiar to me and some not. For Aug.15-16, RW and SW Aquarii were the best candidates, but the only available charts for them covered star fields too small to be useful. For the 16-17th, a barely useful chart for FZ Delphini, an eclipsing binary, was obtained from the AAVSO’s online Charts Library. The asteroid would cross the chart’s extreme northeast corner in just a few minutes, so I observed that area 24 hours early, in a hazy sky, and again 2 to 3 hours early, in order to recognize the intruder.. The latter preparatory work paid off, as did preliminary observations of two familiar variable stars, the Miras W and S Lyrae, through whose “b” chart fields the asteroid would move during its closest approach period. During a 2+ hour interval between these passages, it would cross the field of V Lyrae, another Mira which was new to me. I obtained a b-scale chart for this star, but it was a “reversed” version, for users of Schmidt-Cassegrain or refracting telescopes with erect fields of view. Although it was converted to normal format (South up, West left) by my computer, magnitude values were left unreadable and the new chart would have to be used upside-down because the star field would be north of my zenith when the asteroid passed through it. With only one brief opportunity for preliminary observation of V Lyr’s field, I was ill-prepared for that passage.

On Aug. 17 I acquired FZ Del at 12:45 AM, near the prime meridian and at 65° altitude, and centered a 74X eyepiece with a 48 arc-minute real field somewhat southeast of 2002 NY40’s plotted position for 1:30. (See Chart 1.) Just after 1:00 the asteroid was sighted, near its expected track but approximately 5 minutes “fast,” not surprising since the predicted positions were from an ephemeris over two weeks old. The magnitude was estimated at 10.9 using comparison stars for the variable, and the motion was discernable in under a minute at 140X. The color was pale, dull yellow. I followed the object until 1:40 when its magnitude was 10.8, a little brighter than the predicted 10.9 and a good omen for the next evening.

By dusk on the 17th my equipment and charts were ready, but observation of the asteroid got off to a rough start. A fat gibbous Moon in Sagittarius, while not a severe sky-brightner where I was viewing, shone on the right side of my face and a little into my telescope. With no time to erect a blocking screen, I had to deal with the resulting glare with my right hand while moving the ‘scope with my left one. This disturbance caused me to misdirect the ‘scope downtrack of the expected 9:30 P.M. position plotted on the S Lyr “b” chart (Chart 2), and I recovered barely in time to spot the asteroid there, some 5 minutes early. It was unexpectedly dim, bright 10th magnitude instead of mid-9th, and racing into the area covered by my oddball V Lyr chart. Apparently still in a temporary fade, it eluded me after only 7 or 8 minutes and could not be reacquired as late as 10:15. I quit and treated mosquito bites and rested indoors for almost 2 hours, when another good sighting chance was due and the Moon would be very low. My main concern was for the sky to remain clear.

At 11:55 the asteroid appeared 1° south of Kappa Lyr, on the W Lyr “b” chart (Chart 3), now brighter than expected, white and moving sensibly in 5 seconds at 74X. I followed it to the WSW edge of the chart’s field, estimating its magnitude as 9.0-9.3 maximum but with three dimmings to near 10.0 lasting up to 2 minutes. Leaving W Lyr, the asteroid entered northeastern Hercules and I watched it until 1:10 A.M. on the 18th, still at bright 9th mag. most of the time and easy to recover if ignored for several minutes. A predicted drop of average brightness two to three hours hence was beyond my energy level to observe.

In over 50 years of telescopic observation, I have seen only one moving starlike object as fascinating as 2002 NY40 in its flyby, and it was manmade: Apollo 13 outbound to over 20,000 miles from Earth in April 1973, viewed with my 8-inch ‘scope when it was only 6 years old. Alas, I regret having no actual pictures of the asteroid for this account.


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