Centennial Observatory - Research

Research at the Centennial Observatory

Although the primary purpose of the Centennial Observatory is to provide visitors the opportunity 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 blocked (or occulted) 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 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 appears at far right, in cyan.  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, the location of the paths their shadows (cast by starlight) take across the Earth has some uncertainty to it.  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 twenty-five occultation observations conducted at the Centennial Observatory has resulted in seeing the target star temporarily vanish as an asteroid obscures it.

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 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.)

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
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
27 Jul 2015 (8823) 1987 WS3 HIP 90382 2.2% C. Anderson
B. Hall
Only occ. of this asteroid ever recorded.
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.