On behalf of Prof. Costantino Sigismondi, International Center for Relativistic Astrophysics (ICRA), Italy, we present this very special call for observations:
Introduction:
Measuring the solar diameter during total eclipses is favored by the “on-off” signal of the Baily’s beads formed by the lunar valleys on the solar limbs’ photosphere.
- Sigismondi, C. et al., Convoluzione tra oscuramento al bordo e diffrazione, nell’eclissi solare parziale del 21 giugno 2020, Abstract: https://ui.adsabs.harvard.edu/abs/2020Gerb…13…87S/abstract PDF: https://www.icra.it/gerbertus/2020/Gerb-13-2020-Sigismondi-Parziale-87-96.pdf
During partial eclipses is more difficult: the lunar profile’s contacts timing are obtained from extrapolating video images of the first and last “bites” of Moon at the solar limb. The ability of skilled solar observers united with the UTC synchronized timing familiarity – especially by the IOTA fellows – can permit to get useful data.
This eclipse will be compared with the total one of 2006, and it occurs after a Methon cycle of 19 years with interesting properties of “conservation” of the lunar limbs profiles (the lunar nodes revolve in 18.6 years and the Saros is 18.03 years). The solar activity can also influence the solar diameter, as envisaged by Secchi and Rosa at Collegio Romano in XIX century.
- Sigismondi, C., The Secchi-Rosa law on the solar diameter, https://www.worldscientific.com/doi/10.1142/9789811258251_0266
Video Measurements during the Solar Eclipse:
- Video recordings with cameras with GPS time insterted by timestamps in the picture are prefered.
- Video recording through the telescope’s eyepiece (afocal method) with time reference filmed. The absolute time resolution will be one second with a time reference filmed before and after the event. An example of such a video recording can be found here: https://www.youtube.com/watch?v=oCzOVTxT1tk
Image from the video through the eyepiece:
Settings for the Camera:
- A video in mp4 format is fine, if possible record files with sizes not larger than 100 MB.
- Frame rate of 30 fps is sufficient.
- The resolution of the recording will be limited by seeing, so don’t use a magnification above 50x.
- Record the full disk of the Sun or only the areas of the eclipse.
Time Span for Recording:
- First contact: from -30 s to +240 s
- Fourth contact: from -240s to +30 s
- (There are no 2. and 3. contacts during a partial eclipse)
Prepare your Observation:
- Give your observation technique some practice in the days before.
- The partiality’s ephemerides for your observing location can be retrieved at timeanddate.com. An example for Rome, Italy, is given here: https://www.timeanddate.com/eclipse/in/italy/rome?iso=20250329 or by coordinates: https://www.timeanddate.com/eclipse/in/@41.903267,12.497399
- Table with contact times for major European cites (calculated with Occult V4): Partial Total Eclipse of 2025 Mar 29 – Multisites
After the Observation:
- The video can be sent through grosfichiers.com to sigismondi(at)icra.it and to damico.1988482(at)studenti.uniroma1.it
- All attempts made in this effort, also the clouded ones, will be credited!