Although the primary purpose of the Centennial Observatory is to provide visitors with opportunities to experience the universe visually through telescopes, the facility is also used for astronomical research. The main research focus is the determination of asteroids' sizes and the refinement of their orbits via stellar occultation.
The method is straightforward: A precise measurement of how long a distant star's light is occulted (blocked) by a passing asteroid, together with the asteroid's previously-determined distance and speed, allows the asteroid's diameter to be calculated (by distance = rate x time). This measurement is accomplished via video photometry: video from a high-sensitivity camera attached to the telescope passes through a GPS-based device which "stamps" each video frame with the time (down to millisecond precision), to video recording devices (VHS and direct-to-hard drive). The video is analyzed with software that precisely measures the intensity of the target star in each video frame and assigns it a numerical relative brightness value. The light curve (a graph of brightness vs. time—see fig. 3, below) reveals the duration of the occultation.
With several astronomers observing the same event from various locations around the globe, the size and shape of the asteroid's shadow (identical to that of the asteroid itself, since stars are so distant that their light reaches Earth on essentially-parallel paths) may be mapped out.
Since asteroids' exact orbits (like all measured quantities) are imperfectly known, their shadows (cast by starlight) take paths across the Earth whose exact location is uncertain. While many asteroid occultation observers utilize small, portable instruments which allow them to travel to locations where a given asteroid's shadow is most likely to pass, this option is not available for the Centennial Observatory's permanently-mounted 24" (0.6m) telescope. Therefore we observe many occultations, with probabilities ranging from near-certainty (weather notwithstanding) to less than 1-in-2000, to increase the frequency of success. To date, roughly one out of every fifteen occultation observations conducted at the Centennial Observatory (not including those which were clouded out) has resulted in seeing the target star temporarily vanish as an asteroid obscures it. It should be noted that a close miss is still scientifically useful, as it can also help constrain the asteroid's shape and path (e.g. the red chord at far left in fig. 2).
The Centennial Observatory's first asteroid occultation observation was conducted on 24 August 2012, when asteroid (1585) Union cast its shadow from the star TYC 5777-010444-1 onto the Earth. No occultation was seen (i.e. the shadow missed Twin Falls). All subsequent "positives" (timings performed when the Centennial Observatory was in an asteroid's stellar shadow) are listed below, in reverse chronological order.
Click on the date for a map of the asteroid's predicted shadow path. Click on the asteroid name for a profile of the asteroid showing all observers' chords (star tracks relative to the asteroid as seen from different locations). Click on the star name for a graph of the photometric data. Click on the observers' names for a map of all observers' locations. (Use the "back" button to return to this page.)
|15 Dec 2019||(979) Ilsewa||UCAC4 516-030661||15.8%||C. Anderson||First measurement by occultation since discovery (1922).|
|17 Nov 2019||(163) Erigone||UCAC4 361-199049||62.8%||C. Anderson, A. Holesinsky, K. Snell|
|02 Nov 2019||(120) Lachesis||UCAC4 555-046398||1.7%||C. Anderson|
|30 Sep 2019||(547) Praxedis||UCAC4 441-118948||10.8%||C. Anderson|
|25 Sep 2019||(493) Griseldis||HIP 40716||53.9%||C. Anderson||Video|
|02 Sep 2019||(1259) Ógyalla||UCAC4 568-028403||22.4%||C. Anderson|
|25 Jul 2019||(713) Luscinia||UCAC4 400-078605||66.5%||C. Anderson|
|02 Jul 2019||(517) Edith||UCAC4 333-131777||90.9%||C. Anderson, D. West, A. Holesinsky|
|24 Jun 2019||(52) Europa||UCAC4 441-000722||100.0%||C. Anderson|
|24 Jun 2019||(2906) Caltech||UCAC4 320-120385||37.7%||C. Anderson|
|21 Jun 2019||(91) Aegina||UCAC4 319-115946||82.5%||C. Anderson|
|09 May 2019||(225) Henrietta||TYC 5019-00392-1||69.7%||C. Anderson|
|04 May 2019||(410) Chloris||UCAC4 378-099549||94.0%||C. Anderson|
|25 Apr 2019||(690) Wratislavia||TYC 6751-00068-1||80.9%||C. Anderson|
|01 Feb 2019||(538) Friederike||UCAC4 541-023639||40.1%||C. AndersonS. Korecki||Video (on Facebook)|
|24 Jan 2019||(638) Moira||UCAC4 570-033268||36.0%||C. Anderson|
|23 Jan 2019||(84) Klio||UCAC4 619-016579||51.3%||C. Anderson|
|29 Sep 2018||(671) Carnegia||TYC 2437-00868-1||62.9%||C. Anderson|
|10 Sep 2018||(174567) Varda||4UC 440-067774||5.9%||C. AndersonR. ShowersK. Thomason||Trans-Neptunian Object & dwarf planet candidate|
|15 Aug 2018||(134340) Pluto||4UC 341-187633||20.3%||C. AndersonD. West||Occultation by atmosphere only|
|17 Apr 2018||(137) Meliboea||2UCAC 28992342||92.5%||C. Anderson|
|06 Oct 2017||(1936) Lugano||TYC 1358-00407-1||31.1%||C. Anderson||Video|
|28 Sep 2017||(69) Hesperia||4U 380-139928||99.9%||C. Anderson
|26 Sep 2017||(372) Palma||UCAC4 697-043370||100.0%||C. Anderson|
|09 Aug 2017||(903) Nealley||TYC 5788-00046-1||66.8%||C. Anderson|
|16 Apr 2017||(838) Seraphina||4U 475-43580||31.8%||C. Anderson
|11 Apr 2017||(105) Artemis||HIP 62736||26.3%||C. Anderson
|18 Jan 2017||(52) Europa||2UCAC 28031948||99.9%||C. Anderson||Profile with shape model derived from rotation light curve.|
|22 Oct 2015||(247) Eukrate||TYC 3413-01493-1||57.3%||C. Anderson
|23 Aug 2015||(107) Camilla||TYC 5595-00982-1||88.0%||C. Anderson
|Cited in Astronomy & Astrophysics, 7 Feb 2017. Profile with shape model derived from rotation light curve.|
|27 Jul 2015||(8823) 1987 WS3||HIP 90382||2.2%||C. Anderson
|Only occul- tation of this asteroid recorded to date.|
|12 Feb 2015||(931) Whittemora||TYC 652-01042-1u||14.2%||C. Anderson
|09 Oct 2014||(54) Alexandra||TYC 6308-00865-1||Not rec.||C. Anderson|
The table below includes all the negative observations (misses) recorded at the Centennial Observatory for which at least one other observer recorded a positive, and no other negatives lay between the asteroid's shadow and us. Such misses may also help constrain the asteroid's size and shape (depending on distance from the shadow path, best seen in the profile).
|Local Date||Asteroid||Distance from predicted path*||Prob.||Observers||Notes|
|24 Apr 2019||(386) Siegena||587 mi. (945 km) outside 1-σ||<0.05%||C. Anderson|
|19 Mar 2019||(1072) Malva||14 mi. (23 km) outside 1-σ||4.9%||C. AndersonS. Korecki|
|14 Dec 2018||(164) Eva||52 mi. (84 km) outside 1-σ||<0.05%||C. Anderson|
|21 Sep 2018||(89) Julia||147 mi. (237 km) outside 1-σ||<0.05%||C. Anderson|
|21 Feb 2018||(1328) Devota||475 mi. (764 km) outside 1-σ||<0.05%||C. Anderson|
|21 Feb 2018||(372) Palma||1784 mi. (2871 km) outside 1-σ||<0.05%||C. Anderson|
|19 Oct 2017||(1574) Meyer||17 mi. (27 km) outside 1-σ||5.9%||C. AndersonS. Korecki|
|29 Dec 2016||(446) Aeternitas||<1 mi. (0.6 km) outside shadow||49.1%||C. AndersonD. WestKa. Hansen
|29 Dec 2016||(102) Miriam||665 mi. (1070 km) outside 1-σ||<0.05%||C. AndersonD. West|
|29 Jun 2016||(1796) Riga||194 mi. (312 km) outside 1-σ||<0.05%||C. AndersonS. BarksdaleS. Mauldin|
|11 May 2016||(569) Misa||8 mi. (13 km) outside shadow||41.2%||C. Anderson|
|29 Oct 2014||(393) Lampetia||307 mi. (494 km) outside 1-σ zone||Not rec.||C. Anderson|
*The 1-σ zone (delineated in red on the "Observers" maps) has a 68.27% chance of containing at least some of the asteroid's shadow ("one standard deviation" from the predicted shadow path). The wider 2-σ zone (two standard deviations from the shadow) has a 95.45% chance of containing at least some of the asteroid's shadow.