For your information: There will be a Mercury transit on May 7, 2003, and a coronal transit of Venus on June 8, 2004. It's time to start thinking about potential observing plans (stray light calibrations, pickup ions, etc) for the May 7 transit. Below are the current details from Flight Dynamics for both events. We have initially asked for three hours of DSN telemetry contact on either side of 10:11 UT (the duration of the transit as seen from Earth is 5h19m); DSN availability is as yet unknown - there are three launches in May that could interfere. We have also asked to have a tabulation of the planet's trajectory versus UT time (as seen from SOHO) be calculated after the projected stationkeeping manoeuvre on February 19. Please contact soc@soc.nascom.nasa.gov with any questions or special requests relating to this. Mercury transit details from FDF --------------------------------------------------------------------- Mercury's closest angular approach to the solar center as seen from SOHO will be 0.194 deg, occurring on May 7, 2003 at 10:11:07.776 UTC (A.1 Julian date 2452766.92476632). SOHO's vantage point for this event will be 1,538,930 km closer to the Sun than Earth's, 79,551 km south of the ecliptic plane, and roughly 20.7 degrees west of the Sun as seen from Earth. At this epoch, the photospheric angular radius as seen from SOHO is 0.26690198 deg. So, Mercury's center will appear 0.07290198 deg inside the solar disk, or alternatively, some 72.7% of the way out along the solar radius. Mercury's disk as seen from SOHO will appear to be 12.262 arc seconds across, while the Sun will appear to be 1921.694 arc-sec in diameter. Anyway, here are some other parameters of interest for the instant of closest approach: Sun-Earth distance = 150,949,612 km Sun-SOHO distance = 149,410,682 km SOHO Z(subscript: Ecliptic) position component = -79,551 km (Heliocentric TOD Ecliptic) SOHO-Earth distance = 1,646,316 km Sun-Earth-SOHO angle = 20.697 deg Sun-Mercury distance = 67,355,520 km Mercury Z(subscript: Ecliptic) position component = +240,753 km (Heliocentric TOD Ecliptic) SOHO-Mercury distance = 82,056,205 km Earth-Mercury distance = 83,595,962 km Mercury radius = 2,439 km Mercury angular diameter as seen from SOHO at epoch = 0.0034060655 deg Solar photospheric radius = 696,000 km Solar angular diameter as seen from SOHO at epoch = 0.5338039594 deg Solar angular radius as seen from SOHO at epoch = 0.266901979 deg ----------------------------------------------------------------- Venus (2004) coronal transit details from FDF ----------------------------------------------------------------- Given that Venus will be below the ecliptic for this inferior conjunction, it appears that this event will be seen from Earth to be a transit of the Sun's southern hemisphere. From SOHO's vantage point--being 1,289,765 km closer to the Sun but 83,766 km north of the ecliptic plane and roughly 17 degrees west of the Sun as seen from Earth--the epoch of Venus's closest angular approach to the Sun will be June 8, 2004 13:30:16.894 UTC (A.1 Julian Date 2453165.06307787). At this epoch, the photospheric angular radius as seen from SOHO is 0.26484852 deg. However, Venus's angular separation from the Sun's center at this epoch is 0.3170 deg. Thus, Venus's center misses the photosphere by 0.05215148 deg, or 187.745 arc-sec (or, a little more than three Venus diameters). As Venus presents a disk of 59.536 arc-sec to SOHO, the two disks miss "touching" by 157.977 arc-sec. In short, no transit of the photosphere from SOHO's perspective. The reason is that SOHO will be well north of the ecliptic--were it to be in the southern portion of its halo at this epoch it might well expect a view. Too bad. Anyway, here are some parameters of interest for the instant of closest approach: Sun-Earth distance = 151,858,870 km Sun-SOHO distance = 150,569,105 km SOHO Z(subscript: Ecliptic) position component = +83,766 km (Heliocentric TOD Ecliptic) SOHO-Earth distance = 1,350,602 km Sun-Earth-SOHO angle = 17.1866 deg Sun-Venus distance = 108,642,310 km Venus Z(subscript: Ecliptic) position component = -168,366 km (Heliocentric TOD Ecliptic) SOHO-Venus distance = 41,927,683 km Earth-Venus distance = 43,217,978 km Venus radius = 6,051 km Venus angular diameter as seen from SOHO at epoch = 0.016537845 deg Solar photospheric radius = 696,000 km Solar angular diameter as seen from SOHO at epoch = 0.529697041 deg Solar angular radius as seen from SOHO at epoch = 0.26484852 deg If there are any parameters missing that you are interested in, please let me know and I'll see if I can get them.