Cassini Stargazing? |
Cassini Stargazing? |
Oct 25 2005, 11:22 AM
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#1
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
An activity several days ago had the narrow angle camera pointing to the Pleiades (RA 56.871, dec 24.449). What's that all about? Here's the science plan entry:
BEGIN_TIME: 183256204.182416 (2005 OCT 22 12:29:00 UTC) END_TIME: 183289624.182419 (2005 OCT 22 21:46:00 UTC) PRIMARY_POINTING: ISS_NAC to 56.871/24.449 REQUEST_ID: VIMS_017OT_PLEIADES001_PRIME REQUEST_TITLE: Pleiades REQ_DESCRIPTION: Turn to Pleiades; Time: 30 min Pleiades: multiple cubes w/64x64 FOV IR @ 640 ms, VIS @ 40000 ms; Time: 7.0 hr 47 min; Volume: 86.5 Mbits; CompRatio: 2.0 Turn to waypoint: 30 min Primary: -y to Pleiades; Secondary: +z to TBD Not time critical. RWA REQUIRED. SECONDARY_POINTING: POS_X to NSP SEQUENCE: S15 SUBSYSTEM: VIMS -------------------- |
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Oct 25 2005, 12:01 PM
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#2
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
QUOTE (jmknapp @ Oct 25 2005, 01:22 PM) An activity several days ago had the narrow angle camera pointing to the Pleiades (RA 56.871, dec 24.449). What's that all about? Instrument calibration purposes? Acquiring of stellar spectra for VIMS and PSF, flatfields for the cameras? AFAIK there are supposed to be regular calibration measurements made at least once per year to better understand the instrument performance. -------------------- |
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Guest_Richard Trigaux_* |
Oct 25 2005, 12:50 PM
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#3
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Guests |
QUOTE (ugordan @ Oct 25 2005, 12:01 PM) Instrument calibration purposes? Acquiring of stellar spectra for VIMS and PSF, flatfields for the cameras? AFAIK there are supposed to be regular calibration measurements made at least once per year to better understand the instrument performance. This is understandable, aiming the instruments at known targets to compare their output. The Pleiades were selected perhaps because they offer a great number of stars of varied sizes ( ideal to plot the luminance response curve of the cameras) into only one frame, and also they are very close together (separation power of the cameras). |
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Oct 25 2005, 05:20 PM
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#4
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
QUOTE (Richard Trigaux @ Oct 25 2005, 02:50 PM) This is understandable, aiming the instruments at known targets to compare their output. The Pleiades were selected perhaps because they offer a great number of stars of varied sizes ( ideal to plot the luminance response curve of the cameras) into only one frame, and also they are very close together (separation power of the cameras). The Pleiades seem to be a popular target for in-flight calibration purposes. I recall at least one other mission that used them for camera testing, OTOH it might have been Deep Impact or MESSENGER. -------------------- |
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Oct 25 2005, 05:47 PM
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#5
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Senior Member Group: Moderator Posts: 3233 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
Star clusters are great targets for calibration because their dense...clustering of stars at varied brightnesses allow for montioring of the PSF and the instrument response. HiRISE looked at Omega Centauri, for example, last month.
-------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Oct 25 2005, 05:52 PM
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#6
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
QUOTE (volcanopele @ Oct 25 2005, 12:47 PM) Star clusters are great targets for calibration because their dense...clustering of stars at varied brightnesses allow for montioring of the PSF and the instrument response. HiRISE looked at Omega Centauri, for example, last month. Could Cassini conduct any significant stellar astronomy? It is about a billion miles closer to the rest of the galaxy than we are on Earth. -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Oct 25 2005, 08:20 PM
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#7
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Senior Member Group: Admin Posts: 4763 Joined: 15-March 05 From: Glendale, AZ Member No.: 197 |
QUOTE (ljk4-1 @ Oct 25 2005, 05:52 PM) Could Cassini conduct any significant stellar astronomy? It is about a billion miles closer to the rest of the galaxy than we are on Earth. That's a bit like climbing up a step ladder to get a better look at the moon. -------------------- If Occam had heard my theory, things would be very different now.
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Oct 25 2005, 10:07 PM
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#8
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
I think this is one of the Pleiades images, but can't really tell. The FOV of the narrow angle camera is much less than the width of the Pleiades, so maybe only one bright star is in the field (Alcyone?):
http://saturn.jpl.nasa.gov/multimedia/imag...5/N00042058.jpg -------------------- |
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Oct 26 2005, 11:56 AM
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#9
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
QUOTE (ElkGroveDan @ Oct 25 2005, 03:20 PM) Well, technically, one would be closer to the Moon. Repeating smiley here: -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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Oct 26 2005, 01:22 PM
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#10
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Interplanetary Dumpster Diver Group: Admin Posts: 4404 Joined: 17-February 04 From: Powell, TN Member No.: 33 |
QUOTE (ljk4-1 @ Oct 25 2005, 05:52 PM) Could Cassini conduct any significant stellar astronomy? It is about a billion miles closer to the rest of the galaxy than we are on Earth. Seriously, I read a proposal for an astrometry mission which would be sent on an Interstellar Probe type trajectory. The purpose would be to get a longer baseline for parallax. However, the resolution of Cassini's cameras is not good enough to give it an advantage at Saturn. -------------------- |
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Oct 26 2005, 05:07 PM
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#11
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Member Group: Members Posts: 510 Joined: 17-March 05 From: Southeast Michigan Member No.: 209 |
QUOTE (ljk4-1 @ Oct 26 2005, 07:56 AM) And also quite necessary if one's view of the moon is blocked by one's neighbor's privacy fence -------------------- --O'Dave
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Oct 26 2005, 06:39 PM
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#12
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Junior Member Group: Members Posts: 76 Joined: 19-October 05 Member No.: 532 |
QUOTE (jmknapp @ Oct 25 2005, 11:07 PM) I think this is one of the Pleiades images, but can't really tell. The FOV of the narrow angle camera is much less than the width of the Pleiades, so maybe only one bright star is in the field (Alcyone?): http://saturn.jpl.nasa.gov/multimedia/imag...5/N00042058.jpg nope, this is from ISS_017ST_MONITOR001_PRIME, the bright star is Vega |
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Oct 26 2005, 07:37 PM
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#13
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
QUOTE (pat @ Oct 26 2005, 02:39 PM) Should have known you'd track it down. -------------------- |
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Oct 28 2005, 02:02 PM
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#14
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Senior Member Group: Members Posts: 2454 Joined: 8-July 05 From: NGC 5907 Member No.: 430 |
gr-qc/0510105 [abs, ps, pdf, other] :
Title: A comment on the possibility of testing the Dvali-Gabadadze-Porrati gravity model with the outer planets of the Solar System Authors: Lorenzo Iorio Comments: LaTex, 7 pages, 2 tables, 0 figures, 18 references Subj-class: General Relativity and Quantum Cosmology; Space Physics The multidimensional braneworld gravity model by Dvali, Gabadadze and Porrati was primarily put forth to explain the observed acceleration of the expansion of the Universe without resorting to dark energy. One of the most intriguing features of such a model is that it also predicts small effects on the orbital motion of test particles which could be tested in such a way that local measurements at Solar System scales would allow to get information on the global properties of the Universe. Lue and Starkman derived a secular extra-perihelion \omega precession of 5\times 10^-4 arcseconds per century, while Iorio showed that the mean longitude \lambda is affected by a secular precession of about 10^-3 arcseconds per century. Such effects depend only on the eccentricities e of the orbits via second-order terms: they are, instead, independent of their semimajor axes a. Up to now, the observational efforts focused on the dynamics of the inner planets of the Solar System whose orbits are the best known via radar ranging. Since the competing Newtonian and Einsteinian effects like the precessions due to the solar quadrupole mass moment J2, the gravitoelectric and gravitomagnetic part of the equations of motion reduce with increasing distances, it would be possible to argue that an analysis of the orbital dynamics of the outer planets of the Solar System, with particular emphasis on Saturn because of the ongoing Cassini mission with its precision ranging instrumentation, could be helpful in evidencing the predicted new features of motion. In this note we investigate this possibility in view of the latest results in the planetary ephemeris field. Unfortunately, the current level of accuracy rules out this appealing possibility and it appears unlikely that Cassini and GAIA will ameliorate the situation. http://arxiv.org/abs/gr-qc/0510105 gr-qc/0508012 [abs, ps, pdf, other] : Title: On the impossibility of using certain existing spacecraft for the measurement of the Lense-Thirring effect in the terrestrial gravitational field Authors: Lorenzo Iorio Comments: LaTex2e, 13 pages, no figures, no tables, 31 references. Reference added, Section 2.4 added Subj-class: General Relativity and Quantum Cosmology; Space Physics In the context of the currently ongoing efforts to improve the accuracy and reliability of the measurement of the Lense-Thirring effect in the gravitational field of the Earth it has recently been proposed to use the data from the existing spacecraft endowed with some active mechanisms of compensation of the non-gravitational accelerations like GRACE. In this paper we critically discuss this interesting possibility. Unfortunately, it turns out to be unpracticable because of the impact of the uncancelled even zonal harmonic coefficients of the multipolar expansion of the terrestrial gravitational potential and of some time-dependent tidal perturbations which would resemble as superimposed linear trends over the necessarily limited observational time span of the analysis. http://arxiv.org/abs/gr-qc/0508012 -------------------- "After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance. I see that such intercourse long continued would make one thoroughly prosaic, hard, and coarse. But the longest intercourse with Nature, though in her rudest moods, does not thus harden and make coarse. A hard, sensible man whom we liken to a rock is indeed much harder than a rock. From hard, coarse, insensible men with whom I have no sympathy, I go to commune with the rocks, whose hearts are comparatively soft." - Henry David Thoreau, November 15, 1853 |
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May 29 2006, 02:41 PM
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#15
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Member Group: Members Posts: 531 Joined: 24-August 05 Member No.: 471 |
There is another Deep Sky image online.
Gasgiant Saturn and supergiant Rigel: - PIA08187: Help from Orion -------------------- - blue_scape / Nico -
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