ISSAT Observations of Tempel 1 / Deep Impact

In July 2005, I was a member of the ISSAT team that observed the Deep Impact spacecraft's collistion with Comet Tempel 1. This page summarizes our observations with a cpmposite image of the event, a graph of the brightness of the comet nucleus, and a table summarizing the photometric measurements that we made.

The ISSAT is a 14-inch SCT located at the Arizona Sky Village in Portal, AZ. It is equipped with an SBIG ST9 CCD camera. We controlled the telescope and camera remotely from Dyer Observatory in Nashville, TN, and carried out the analysis and compositing of the images in Lyons, OR.

The observing team consisted of A.G. Kasselburg, Terry Mann, Rocky Alvey, and me (Richard Berry). The ISSAT is the ground-based part of a project sponsored by the Astronomical League to place an amateur-operated astronomical telescope on the International Space Station. In NASA's current budget climate, it is highly unlikely that the project will ever result in an amateur telescope in space, but the existing ground station can be operated by and for amateur astronomers.

Above is a composite image made from the 230-some images we made. The composite is registered on the star background, and shows every tenth image. To facilitate good time resolution each exposure was 30 seconds; to allow rapid downloading of the data, we binned the ST9's images 2x2, so the original images were 256 pixels on a side. Because the telescope was not tracking at exactly the right rate, the observers had to recenter the comet every 20 images or so.

The motion of the comet is from upper right to lower left. The sudden brightening of the comet by a factor of approximately four is quite obvious. The last several images in the composite are blurry because the comet was low in the sky; the sequence ended when the comet set behind mountains at the observing site.

Below is a photometric light curve. The pale yellow points plot the differential magnitude between the comet and an ensemble of four stars (the prominent quadrilateral at lower center on the composite image). Before the impact, the differential magnitude (V-Ens, i.e., Variable minus Ensemble) was approximately +0.7. Beginning at 5:49:02, our images show a rapid increase in brightness that leveled off around V-Ens = -0.7 by approximately 6:30:00. The difference of ~1.4 magnitudes is roughly a factor of four.

The green points plot the differential magnitude between comparison star C1 (the star closest to the comet's track) and the Ensemble. This plot remained nearly flat, indicating that atmospheric extinction was reasonably well compensated during the observing run.

Below is the data behind the photometric light curve plotted above. Listed are the date, time, Julian Day, differential magnitude, standard deviation of the differential magntidue (ie., the size of the "error bar" for the individual observation), the sky brightness measured from the images, and the name of the image.

Date [UT]	Time [UT]	JD	V-Ens [mag]	SD	Sky [ADU]	Filename
7/4/2005	05:39:57.000	2453555.736	0.667	0.061	116.808	tempel-140.fit
7/4/2005	05:40:33.000	2453555.736	0.623	0.063	119.587	tempel-141.fit
7/4/2005	05:41:42.000	2453555.737	0.689	0.060	116.685	tempel-142.fit
7/4/2005	05:42:18.000	2453555.738	0.738	0.058	116.093	tempel-143.fit
7/4/2005	05:42:54.000	2453555.738	0.702	0.057	116.709	tempel-144.fit
7/4/2005	05:43:30.000	2453555.739	0.805	0.057	116.071	tempel-145.fit
7/4/2005	05:44:06.000	2453555.739	0.695	0.058	116.089	tempel-146.fit
7/4/2005	05:44:42.000	2453555.739	0.672	0.063	115.721	tempel-147.fit
7/4/2005	05:45:18.000	2453555.740	0.696	0.060	121.290	tempel-148.fit
7/4/2005	05:46:02.000	2453555.740	0.705	0.059	116.052	tempel-149.fit
7/4/2005	05:46:38.000	2453555.741	0.727	0.060	117.272	tempel-150.fit
7/4/2005	05:47:14.000	2453555.741	0.737	0.061	116.081	tempel-151.fit
7/4/2005	05:47:50.000	2453555.742	0.723	0.061	118.052	tempel-152.fit
7/4/2005	05:48:26.000	2453555.742	0.701	0.062	117.690	tempel-153.fit
7/4/2005	05:49:02.000	2453555.742	0.716	0.061	116.892	tempel-154.fit
7/4/2005	05:49:38.000	2453555.743	0.628	0.068	116.566	tempel-155.fit
7/4/2005	05:50:14.000	2453555.743	0.721	0.060	116.498	tempel-156.fit
7/4/2005	05:50:50.000	2453555.744	0.701	0.059	116.196	tempel-157.fit
7/4/2005	05:51:26.000	2453555.744	0.720	0.064	116.077	tempel-158.fit
7/4/2005	05:52:02.000	2453555.744	0.711	0.062	117.133	tempel-159.fit
7/4/2005	05:52:38.000	2453555.745	0.668	0.059	116.257	tempel-160.fit
7/4/2005	05:53:14.000	2453555.745	0.496	0.059	116.342	tempel-161.fit
7/4/2005	05:53:50.000	2453555.746	0.490	0.054	118.277	tempel-162.fit
7/4/2005	05:54:28.000	2453555.746	0.524	0.054	117.1502	tempel-163.fit
7/4/2005	05:54:43.000	2453555.746	0.369	0.055	117.647	tempel-164.fit
7/4/2005	05:55:19.000	2453555.747	0.388	0.054	116.616	tempel-165.fit
7/4/2005	05:55:55.000	2453555.747	0.324	0.053	117.772	tempel-166.fit
7/4/2005	05:56:34.000	2453555.748	0.255	0.053	117.816	tempel-167.fit
7/4/2005	05:57:10.000	2453555.748	0.316	0.053	119.011	tempel-168.fit
7/4/2005	05:57:46.000	2453555.748	0.269	0.053	117.678	tempel-169.fit
7/4/2005	05:58:22.000	2453555.749	0.240	0.050	117.585	tempel-170.fit
7/4/2005	05:58:58.000	2453555.749	0.168	0.055	119.066	tempel-171.fit
7/4/2005	05:59:34.000	2453555.750	0.130	0.053	119.401	tempel-172.fit
7/4/2005	06:02:35.000	2453555.752	0.000	0.052	118.444	tempel-177.fit
7/4/2005	06:03:47.000	2453555.753	-0.201	0.060	116.745	tempel-179.fit
7/4/2005	06:04:23.000	2453555.753	-0.094	0.057	118.096	tempel-180.fit
7/4/2005	06:04:59.000	2453555.753	-0.211	0.053	117.471	tempel-181.fit
7/4/2005	06:05:35.000	2453555.754	-0.237	0.051	117.930	tempel-182.fit
7/4/2005	06:06:11.000	2453555.754	-0.193	0.048	116.695	tempel-183.fit
7/4/2005	06:06:47.000	2453555.755	-0.285	0.049	116.417	tempel-184.fit
7/4/2005	06:07:23.000	2453555.755	-0.311	0.049	117.148	tempel-185.fit
7/4/2005	06:07:59.000	2453555.756	-0.331	0.047	115.974	tempel-186.fit
7/4/2005	06:08:35.000	2453555.756	-0.369	0.049	117.967	tempel-187.fit
7/4/2005	06:09:12.000	2453555.756	-0.421	0.050	117.467	tempel-188.fit
7/4/2005	06:09:48.000	2453555.757	-0.412	0.051	117.082	tempel-189.fit
7/4/2005	06:10:24.000	2453555.757	-0.420	0.050	116.978	tempel-190.fit
7/4/2005	06:11:00.000	2453555.758	-0.463	0.049	116.675	tempel-191.fit
7/4/2005	06:11:37.000	2453555.758	-0.492	0.050	117.605	tempel-192.fit
7/4/2005	06:12:13.000	2453555.758	-0.471	0.050	117.153	tempel-193.fit
7/4/2005	06:12:49.000	2453555.759	-0.545	0.052	116.589	tempel-194.fit
7/4/2005	06:13:25.000	2453555.759	-0.586	0.053	116.657	tempel-195.fit
7/4/2005	06:14:01.000	2453555.760	-0.521	0.048	116.552	tempel-196.fit
7/4/2005	06:14:37.000	2453555.760	-0.594	0.049	118.294	tempel-197.fit
7/4/2005	06:15:13.000	2453555.761	-0.633	0.052	117.802	tempel-198.fit
7/4/2005	06:17:00.000	2453555.762	-0.606	0.051	117.751	tempel-201.fit
7/4/2005	06:17:36.000	2453555.762	-0.666	0.054	116.834	tempel-202.fit
7/4/2005	06:18:12.000	2453555.763	-0.639	0.052	116.672	tempel-203.fit
7/4/2005	06:18:48.000	2453555.763	-0.730	0.054	116.719	tempel-204.fit
7/4/2005	06:19:24.000	2453555.763	-0.696	0.055	117.343	tempel-205.fit
7/4/2005	06:20:00.000	2453555.764	-0.700	0.052	116.577	tempel-206.fit
7/4/2005	06:20:36.000	2453555.764	-0.704	0.051	117.452	tempel-207.fit
7/4/2005	06:21:12.000	2453555.765	-0.717	0.051	117.154	tempel-208.fit
7/4/2005	06:21:48.000	2453555.765	-0.691	0.052	117.471	tempel-209.fit
7/4/2005	06:22:24.000	2453555.766	-0.721	0.050	116.882	tempel-210.fit
7/4/2005	06:23:00.000	2453555.766	-0.679	0.058	118.047	tempel-211.fit
7/4/2005	06:23:36.000	2453555.766	-0.676	0.051	118.137	tempel-212.fit
7/4/2005	06:26:34.000	2453555.768	-0.720	0.059	118.757	tempel-217.fit
7/4/2005	06:27:10.000	2453555.769	-0.697	0.057	119.000	tempel-218.fit
7/4/2005	06:27:46.000	2453555.769	-0.759	0.058	118.196	tempel-219.fit
7/4/2005	06:28:22.000	2453555.77	-0.749	0.058	117.196	tempel-220.fit
7/4/2005	06:28:58.000	2453555.77	-0.754	0.057	117.605	tempel-221.fit
7/4/2005	06:29:34.000	2453555.771	-0.738	0.059	117.985	tempel-222.fit
7/4/2005	06:30:10.000	2453555.771	-0.719	0.060	119.493	tempel-223.fit
7/4/2005	06:30:46.000	2453555.771	-0.708	0.058	118.647	tempel-224.fit
7/4/2005	06:31:22.000	2453555.772	-0.734	0.061	119.709	tempel-225.fit
7/4/2005	06:31:58.000	2453555.772	-0.673	0.056	120.140	tempel-226.fit
7/4/2005	06:32:34.000	2453555.773	-0.746	0.060	119.269	tempel-227.fit
7/4/2005	06:33:10.000	2453555.773	-0.779	0.060	118.636	tempel-228.fit
7/4/2005	06:33:46.000	2453555.773	-0.749	0.056	118.904	tempel-229.fit
7/4/2005	06:34:22.000	2453555.774	-0.745	0.056	118.433	tempel-230.fit

Here is what the camera on the "mother ship" saw when the probe hit the comet:

For more on the Deep Impact Mission, do a Google search for "Deep Impact Comet Tempel 1."

Observing Deep Impact / Tempel 1