2021-09-29, 04:16 AM
Thank you, good tips!
One more question if you don't mind. I suppose that in the past spaceweather.com used to show the apparent magnitude of the object as the legend below the table contains "MAG is the visual magnitude of the asteroid on the date of closest approach" even though there's no MAG column. I found recent magnitude measurements via MPC (eg https://www.minorplanetcenter.net/db_sea...ommit=Show) but no estimation about the expected magnitude in the near future at various moments.
Do you use the ephemeris calculated by HORIZONS for the latter? If yes, it seems to be something to be calculated by the user. We get the "approximate apparent airless visual magnitude" and the atmospheric "visual magnitude extinction" (a value, in magnitudes, to be substracted, so the apparent visual magnitude would be APmag-mag_ex) . I'm asking not because I cannot substract the numbers :-), just to be sure I'd do the correct thing.
Thanks again,
Razvan
'a-mass mag_ex' =
RELATIVE optical airmass and visual magnitude extinction. Airmass is the
ratio between the absolute optical airmass for the targets' refracted CENTER
point to the absolute optical airmass at zenith. Also output is the estimated
visual magnitude extinction due to the atmosphere, as seen by the observer.
AVAILABLE ONLY FOR TOPOCENTRIC EARTH SITES WHEN THE TARGET IS ABOVE THE
HORIZON. Units: none (airmass) and magnitudes (extinction).
'APmag S-brt' =
The asteroids' approximate apparent airless visual magnitude and surface
brightness using the standard IAU H-G system magnitude model:
APmag = H + 5*log10(delta) + 5*log10® - 2.5*log10((1-G)*phi_1 + G*phi_2)
For solar phase angles >90 deg, the error could exceed 1 magnitude. For
phase angles >120 degrees, output values are rounded to the nearest integer to
indicate error could be large and unknown. For Earth-based observers, the
estimated dimming due to atmospheric absorption (extinction) is available as
a separate, requestable quantity.
************************************************************
Date__(UT)__HR:MN Azi_(a-appr)_Elev a-mass mag_ex APmag
************************************************************
2021-Sep-29 00:00 8.5344 -1.3300 n.a. n.a. 16.569
2021-Sep-29 01:00 16.8881 -1.8994 n.a. n.a. 16.718
2021-Sep-29 02:00 25.8320 -1.1728 n.a. n.a. 16.878
2021-Sep-29 03:00 35.1346 0.9918 23.463 6.595 17.046
2021-Sep-29 04:00 44.5732 4.6259 10.661 2.997 17.221
2021-Sep-29 05:00 54.0028 9.6522 5.721 1.608 17.401
2021-Sep-29 06:00 63.4057 15.9074 3.594 1.010 17.583
2021-Sep-29 07:00 72.9221 23.1689 2.525 0.710 17.766
2021-Sep-29 08:00 82.8839 31.1690 1.926 0.541 17.950
2021-Sep-29 09:00 93.8913 39.5822 1.566 0.440 18.132
2021-Sep-29 10:00 106.9797 47.9628 1.345 0.378 18.311
2021-Sep-29 11:00 123.8652 55.5913 1.211 0.340 18.488
2021-Sep-29 12:00 146.7066 61.1958 1.140 0.321 18.660
2021-Sep-29 13:00 175.1863 62.9367 1.122 0.315 18.829
2021-Sep-29 14:00 202.8923 59.7962 1.156 0.325 18.994
2021-Sep-29 15:00 224.3186 52.8236 1.254 0.352 19.
2021-Sep-29 16:00 239.9649 43.6543 1.446 0.407 19.
2021-Sep-29 17:00 252.0321 33.3527 1.814 0.510 19.
2021-Sep-29 18:00 262.1551 22.4990 2.595 0.729 20.
2021-Sep-29 19:00 271.3757 11.4395 4.894 1.376 20.
2021-Sep-29 20:00 280.4221 0.4308 27.626 7.766 20.
2021-Sep-29 21:00 289.9089 -10.2780 n.a. n.a. 20.
2021-Sep-29 22:00 300.4639 -20.3833 n.a. n.a. 20.
2021-Sep-29 23:00 312.7928 -29.4580 n.a. n.a. 20.
2021-Sep-30 00:00 327.6099 -36.8806 n.a. n.a. 20.
2021-Sep-30 01:00 345.2430 -41.8212 n.a. n.a. 21.
2021-Sep-30 02:00 4.8873 -43.4559 n.a. n.a. 21.
2021-Sep-30 03:00 24.4619 -41.4555 n.a. n.a. 21.
One more question if you don't mind. I suppose that in the past spaceweather.com used to show the apparent magnitude of the object as the legend below the table contains "MAG is the visual magnitude of the asteroid on the date of closest approach" even though there's no MAG column. I found recent magnitude measurements via MPC (eg https://www.minorplanetcenter.net/db_sea...ommit=Show) but no estimation about the expected magnitude in the near future at various moments.
Do you use the ephemeris calculated by HORIZONS for the latter? If yes, it seems to be something to be calculated by the user. We get the "approximate apparent airless visual magnitude" and the atmospheric "visual magnitude extinction" (a value, in magnitudes, to be substracted, so the apparent visual magnitude would be APmag-mag_ex) . I'm asking not because I cannot substract the numbers :-), just to be sure I'd do the correct thing.
Thanks again,
Razvan
'a-mass mag_ex' =
RELATIVE optical airmass and visual magnitude extinction. Airmass is the
ratio between the absolute optical airmass for the targets' refracted CENTER
point to the absolute optical airmass at zenith. Also output is the estimated
visual magnitude extinction due to the atmosphere, as seen by the observer.
AVAILABLE ONLY FOR TOPOCENTRIC EARTH SITES WHEN THE TARGET IS ABOVE THE
HORIZON. Units: none (airmass) and magnitudes (extinction).
'APmag S-brt' =
The asteroids' approximate apparent airless visual magnitude and surface
brightness using the standard IAU H-G system magnitude model:
APmag = H + 5*log10(delta) + 5*log10® - 2.5*log10((1-G)*phi_1 + G*phi_2)
For solar phase angles >90 deg, the error could exceed 1 magnitude. For
phase angles >120 degrees, output values are rounded to the nearest integer to
indicate error could be large and unknown. For Earth-based observers, the
estimated dimming due to atmospheric absorption (extinction) is available as
a separate, requestable quantity.
************************************************************
Date__(UT)__HR:MN Azi_(a-appr)_Elev a-mass mag_ex APmag
************************************************************
2021-Sep-29 00:00 8.5344 -1.3300 n.a. n.a. 16.569
2021-Sep-29 01:00 16.8881 -1.8994 n.a. n.a. 16.718
2021-Sep-29 02:00 25.8320 -1.1728 n.a. n.a. 16.878
2021-Sep-29 03:00 35.1346 0.9918 23.463 6.595 17.046
2021-Sep-29 04:00 44.5732 4.6259 10.661 2.997 17.221
2021-Sep-29 05:00 54.0028 9.6522 5.721 1.608 17.401
2021-Sep-29 06:00 63.4057 15.9074 3.594 1.010 17.583
2021-Sep-29 07:00 72.9221 23.1689 2.525 0.710 17.766
2021-Sep-29 08:00 82.8839 31.1690 1.926 0.541 17.950
2021-Sep-29 09:00 93.8913 39.5822 1.566 0.440 18.132
2021-Sep-29 10:00 106.9797 47.9628 1.345 0.378 18.311
2021-Sep-29 11:00 123.8652 55.5913 1.211 0.340 18.488
2021-Sep-29 12:00 146.7066 61.1958 1.140 0.321 18.660
2021-Sep-29 13:00 175.1863 62.9367 1.122 0.315 18.829
2021-Sep-29 14:00 202.8923 59.7962 1.156 0.325 18.994
2021-Sep-29 15:00 224.3186 52.8236 1.254 0.352 19.
2021-Sep-29 16:00 239.9649 43.6543 1.446 0.407 19.
2021-Sep-29 17:00 252.0321 33.3527 1.814 0.510 19.
2021-Sep-29 18:00 262.1551 22.4990 2.595 0.729 20.
2021-Sep-29 19:00 271.3757 11.4395 4.894 1.376 20.
2021-Sep-29 20:00 280.4221 0.4308 27.626 7.766 20.
2021-Sep-29 21:00 289.9089 -10.2780 n.a. n.a. 20.
2021-Sep-29 22:00 300.4639 -20.3833 n.a. n.a. 20.
2021-Sep-29 23:00 312.7928 -29.4580 n.a. n.a. 20.
2021-Sep-30 00:00 327.6099 -36.8806 n.a. n.a. 20.
2021-Sep-30 01:00 345.2430 -41.8212 n.a. n.a. 21.
2021-Sep-30 02:00 4.8873 -43.4559 n.a. n.a. 21.
2021-Sep-30 03:00 24.4619 -41.4555 n.a. n.a. 21.