Great photos, Jia Hao! I especially like the animated gif.
As stated earlier, I will now add a few more details about our observing experience of Asteroid 2012 DA14's fly-by of Earth (on 15 February 2013 UTC time / Sat 16 February 2013 Singapore time):
- How did Asteroid 2012 DA14 look like in the eyepiece? Well, to me it appeared just as a pin-point white dot, similar in appearance to a star of equivalent magnitude. I could not detect any size or shape to the object whether at 143x or 300x. This is unlike, for example, the main moons of Jupiter which are seen as a distended disc at high powers, esp with larger scopes. Colour-wise, the asteroid appeared as plain white or grey, with no trace or hint of a hue. That was different from many man-made satellites seen with the unaided eye or through the scope, which appear yellowish.
- The brightness of the asteroid changed a lot in the span of that 3 hours. We first saw it in the eyepiece of my LX-90 at around 2.05am (which I recorded as the time of first sighting) when it was at a southerly declination of -62 deg in Centaurus, to the right of Acrux, with an elevation of 25 degrees above the southern horizon and mired in thin cloud cover. At that time, it was at around mag 9, quite faint but readily viewable with direct vision. The moment of first sighting was quite exhilarating!
Later on, when it was near the point of closest approach at 3:24am in Crater (near the border with Leo and Virgo), it was obviously much brighter and contrasty at around mag 6+; that part of the sky was also clearer for the most part. It was then at an elevation of around 80 degrees, almost overhead of us (it was then overflying nearby Sumatra). I managed to view the asteroid into 3:24am, but a few seconds later it dimmed out and was no longer seen; I think it was due to cloud cover rather than the asteroid entering into Earth's shadow. It was at this time that it also moved fastest, crossing the whole field of view of the 14mm eyepiece in 27 seconds.
When we last saw the asteroid at around 4:50am, it had very noticeably dimmed a lot, and was moving at a much slower rate. By then, the asteroid was in the north at declination +50 deg and in Ursa Major (near the Big Dipper), and at an elevation of 34 deg above the northern horizon.
Therefore, in that roughly 2 hours and 45 mins, we saw the asteroid traverse through around 112 degrees of declination (-62 dec to +50 dec): only in the tropics! Now that's a really fast moving natural object still in orbit around the Sun!
- As stated before, we had to constantly use the arrow keys on the Autostar handbox to keep the asteroid in the field of view of the eyepiece, even though the telescope was then doing its normal tracking at sidereal rate. It was like playing some computer game, called "Follow the Asteroid". I set the speed on the Autostar to number 4 (16x sidereal), which was ideal. Whenever anyone was about to let another person take over viewing the asteroid, he had to place it at the edge of the field of view, so that it would be somewhere near the center when the other person took over the viewing and the controls. I think Zong Hao was the most heroic, having once followed the asteroid for around 10 mins as it jumped in and out of clouds. I think I managed a 5 min continuous stretch of viewing.
- It was also quite intriguing watching the asteroid head towards some stars in the eyepiece. I had hoped to see an actual occultation, but the closest I saw was the asteroid whisking by a star at a "close approach" of around 1 arc sec. I think Jia Hao saw an occultation, not sure. I had earlier hand-plotted the path of the asteroid on my Sky & Telescope Pocket Star Atlas and identified some bright star occultation candidates. Unfortunately, the cloud cover was too variable, and the process of bringing the asteroid into the field of view too time-consuming, for me to follow up on that.
- The process of locating the asteroid was as follows: I had earlier generated minute-by-minute celestial coordinates of the asteroid using the NASA JPL Horizons interface (
http://ssd.jpl.nasa.gov/horizons.cgi), set for our precise viewing location at East Coast Park, and stored it as a .txt file on my Android phone. I had generated an updated set of coordinates just a few hours before the viewing sesson. When we wanted to view the asteroid, I would use an atomic-clock app to ascertain the correct present time, e.g. 3:05am. Then I would key in the asteroid's coordinates for about 3-5 mins later, e.g. 3:08am. The Autostar would then point the scope at a nearby star for a "High Precision" centering in the eyepiece; once done it would then slew to the keyed-in coordinates for the asteorid. We then awaited the asteroid's appearance in the eyepiece near the appointed time. And then, bingo! There it is, the asteroid entered into the field of view! This process worked about 8-10 times, and there was perhaps 1 or 2 failures for unknown reasons.
- To tell the truth, I had all-along prior to first spotting the asteroid harboured a slight doubt that NASA had done its calculations correctly, e.g. my moon-gravity effect question. If their calculations were wrong, then our region would be the region of impact, considering the asteroid's approach from the south for a closest approach over nearby Sumatra. So an impact into the Indian Ocean off western Australia, generating a huge tsunami, was considered a possibility. If it crashed into the South China Sea south of Singapore, then hopefully Batam island would shield our sea-side observing site!
I even said that if we saw the asteroid in the sky with unaided eyes getting very bright, then it was time to run for cover. Perhaps down into the MRT tunnels!
However, of course, as we viewed the asteroid in the eyepiece exactly where it was predicted to be, and no brighter too, I felt assurred that there would be no surprises. But what if it crashed into a satellite and got deflected off-course? Ooops.
Anyway, our observations proved to us that NASA's calculations and assumptions were correct, at least down to a few arc minutes.
- When we were viewing the asteroid, I think it was then under the influence of Earth's gravitational field (its orbit was then being perturbed by it) and was getting a significant slingshot-effect boost. As we bid the asteroid farewell at 4:50am, we felt quite safe as it was then heading away from Earth. See you asteroid 2012 DA14, and thanks for the show!
- Finally, I wish to pay tribute and express thanks to NASA-JPL for so kindly making their Horizons interface available to the public around the world. Our viewing would not have been quite possible without those precise coordinates, certainly not at 143x magnification! I also wish to pay tribute to my reliable 12 year old Meade LX-90 8" SCT for its very stable, accurate and precise goto capabilities. Another American product! Below is a photo of the scope taken that night at the field. I had bought and taken delivery of the new LX-90 (the "Classic" model) in January 2001, just a few months after the product launch.
- And right below is a .gif animation made with 7 frames taken through the telescope at prime focus (2000mm). Canon EOS 60D dSLR. Each frame at ISO 3200 and 5 seconds.
