https://skyhound.com/forums/ Fri, 03 Apr 2026 22:20:33 +0000 MyBB https://skyhound.com/forums/showthread.php?tid=2530 Thu, 12 May 2022 18:07:28 -0400 bigmasterdrago]]> https://skyhound.com/forums/showthread.php?tid=2530
Tom Polakis has been imaging these 12th and 13th magnitude rocks for several nights. https://pbase.com/polakis/image/172595509

From my location the minimum separation of these two rocks would be 4.3 arc seconds at 6:04UT on the 13th. But 30+° below my SW horizon.]]>
Tom Polakis has been imaging these 12th and 13th magnitude rocks for several nights. https://pbase.com/polakis/image/172595509

From my location the minimum separation of these two rocks would be 4.3 arc seconds at 6:04UT on the 13th. But 30+° below my SW horizon.]]> https://skyhound.com/forums/showthread.php?tid=611 Wed, 11 Sep 2019 17:17:08 -0400 theskyhound]]> https://skyhound.com/forums/showthread.php?tid=611
This comet was only recognized yesterday as being of interstellar origin (a first). It is currently brighter than 19th mag.]]>
This comet was only recognized yesterday as being of interstellar origin (a first). It is currently brighter than 19th mag.]]> https://skyhound.com/forums/showthread.php?tid=157 Tue, 27 Feb 2018 15:52:54 -0500 ncwolfie]]> https://skyhound.com/forums/showthread.php?tid=157 I have downloaded the MPCOrb.dat file, then tried update by the to read option but nothing gets updated.


Thanks
Randy]]> I have downloaded the MPCOrb.dat file, then tried update by the to read option but nothing gets updated.


Thanks
Randy]]> https://skyhound.com/forums/showthread.php?tid=35 Tue, 02 Jan 2018 13:06:52 -0500 ncwolfie]]> https://skyhound.com/forums/showthread.php?tid=35
Thanks and best regards,
Randy]]>
Thanks and best regards,
Randy]]> https://skyhound.com/forums/showthread.php?tid=15 Thu, 16 Nov 2017 20:13:58 -0500 theskyhound]]> https://skyhound.com/forums/showthread.php?tid=15
As with most of my imaging these days, this was a SkyTools 4 test. A little backstory first: stellar and diffuse objects are modeled differently. A diffuse object, such as a nebula or galaxy, is modeled as one typical image pixel sampling a continuous surface brightness. A stellar object is modeled as a Gaussian Point Spread function. The details aren't really important-what matters is that comets are both of these things, and to varying degrees depending on the comet. Some comets look like stars with no visible coma, while others are completely diffuse, with no central bright spot. Most lie somewhere in between. This makes comets really difficult to model.

SkyTools 4 told me that comet 250P/Larsen would be high in the sky at around 3 AM, and with an integrated magnitude of 19.1, SkyTools predicted that it would be a difficult target. In fact, SkyTools predicted that even once I stacked three 4-min exposures the Signal to Noise Ratio (SNR) would only be 8. An SNR of at least 5 is typically required to do fairly accurate astrometry. So SkyTools was predicting that this would be a marginal observation.

And indeed it was! The SNR measured by Astrometrica was 6, which is quite close. This relatively small difference is actually quite remarkable, given how difficult comets are to model. Being able to fairly accurately predict how long of an exposure is required to obtain good astrometry is a rather useful thing!

Incidentally, SkyTools 4 also told me that the comet would only move by 3 pixels over the course of the three exposures, and that it would move by 1 pixel during each of them.

  Astrometrica.png (Size: 245.62 KB / Downloads: 35) ]]>
As with most of my imaging these days, this was a SkyTools 4 test. A little backstory first: stellar and diffuse objects are modeled differently. A diffuse object, such as a nebula or galaxy, is modeled as one typical image pixel sampling a continuous surface brightness. A stellar object is modeled as a Gaussian Point Spread function. The details aren't really important-what matters is that comets are both of these things, and to varying degrees depending on the comet. Some comets look like stars with no visible coma, while others are completely diffuse, with no central bright spot. Most lie somewhere in between. This makes comets really difficult to model.

SkyTools 4 told me that comet 250P/Larsen would be high in the sky at around 3 AM, and with an integrated magnitude of 19.1, SkyTools predicted that it would be a difficult target. In fact, SkyTools predicted that even once I stacked three 4-min exposures the Signal to Noise Ratio (SNR) would only be 8. An SNR of at least 5 is typically required to do fairly accurate astrometry. So SkyTools was predicting that this would be a marginal observation.

And indeed it was! The SNR measured by Astrometrica was 6, which is quite close. This relatively small difference is actually quite remarkable, given how difficult comets are to model. Being able to fairly accurately predict how long of an exposure is required to obtain good astrometry is a rather useful thing!

Incidentally, SkyTools 4 also told me that the comet would only move by 3 pixels over the course of the three exposures, and that it would move by 1 pixel during each of them.

  Astrometrica.png (Size: 245.62 KB / Downloads: 35) ]]>