Centennial Observatory - Research

Research at the Centennial Observatory

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.

Predicted shadow path of asteroid (105) Artemis via the starlight of HIP 62736, 11 April 2017
Fig. 1: Predicted shadow path of asteroid (105) Artemis, as cast on Earth by HIP 62736, a mag. 8.7 star in Virgo, on 11 April 2017.  The northward-moving shadow was expected to pass east of the Centennial Observatory, but uncertainty in the asteroid's precise orbital path allowed for a 26.3% chance that the shadow would pass over Twin Falls (which it did).

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.

Stellar occultation by asteroid (105) Artemis, 11 April 2017
Fig. 2: Profile of asteroid (105) Artemis as determined by its occultation of HIP 62736 on 11 April 2017.  Diagonal lines represent the star's apparent path, relative to the asteroid, as seen by observers at different locations.  The widths of the gaps ("chords") are determined by the duration of HIP 62736's disappearance as recorded by each observer.  The Centennial Observatory's chord is cyan, at far right.  The asteroid passed a bit to the southwest of its predicted path (dotted line).  (Note the 100 km scale bar at bottom.)

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).

Photometric light curve of the occulatation of HIP 62736 by (105) Artemis, 11 April 2017
Fig. 3: Light curve of the 11 April 2017 (105) Artemis occultation, as derived by photometric video analysis.  The jagged shape of the curve is due to a combination of signal noise and atmospheric distortion.  For just over four seconds, the light of HIP 62736 was blocked by (105) Artemis, causing the signal to drop by around 85% (from the combined light of the star and asteroid, to the light of the much fainter asteroid alone plus background sky glow).

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.)

Positive Asteroid Occultations Recorded at the Centennial Observatory

Date (GMT)AsteroidStarProb.Observers*Notes
18 Feb 2020 (148) Gallia UCAC4 497-046647 35.2% C. Anderson, A. Holesinsky
08 Feb 2020 (32615) 2001 QU277 UCAC4 512-052944 6.8% C. Anderson Jovian Trojan asteroid; first measurement by occultation.
27 Jan 2020 (2634) James Bradley UCAC4 545-023716 21.8% C. Anderson First measurement by occultation since discovery (1982).
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. Anderson
S. 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. Anderson
R. Showers
K. Thomason
Trans-Neptunian Object & dwarf planet candidate
15 Aug 2018 (134340) Pluto 4UC 341-187633 20.3% C. Anderson
D. 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
K. Hansen
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
K. Hansen
K. Hansen
11 Apr 2017 (105) Artemis HIP 62736 26.3% C. Anderson
et al.
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
S. Barksdale
23 Aug 2015 (107) Camilla TYC 5595-00982-1 88.0% C. Anderson
B. Hall
J. Royalty
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
B. Hall
Only occul- tation of this asteroid recorded to date.
12 Feb 2015 (931) Whittemora TYC 652-01042-1u 14.2% C. Anderson
D. West
09 Oct 2014 (54) Alexandra TYC 6308-00865-1 Not rec. C. Anderson

*At the Centennial Observatory.  Observers in other locations not listed.

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).

Significant Asteroid Occultation Misses Recorded at the Centennial Observatory

Local DateAsteroidDistance from predicted path*Prob.ObserversNotes
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. Anderson
S. 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. Anderson
S. Korecki
29 Dec 2016 (446) Aeternitas <1 mi. (0.6 km) outside shadow 49.1% C. Anderson
D. West
Ka. Hansen
Ky. Hansen
29 Dec 2016 (102) Miriam 665 mi. (1070 km) outside 1-σ <0.05% C. Anderson
D. West
29 Jun 2016 (1796) Riga 194 mi. (312 km) outside 1-σ <0.05% C. Anderson
S. Barksdale
S. 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.