Context: Recently Polar Sundial designed by the Vikram Sarabhai Space Centre (VSSC), is displayed in the ‘Rocket Garden’ of its Space Museum in Thumba.
- Sundials are devices that measure time by using the shadow cast by the sun’s position in the sky.
- Sundials have been used since 1500 BCE in Ancient Egypt and Babylon, they were essential for measuring time before modern clocks.
- India’s Contribution: India has a rich history in sundial science, evident in 18th-century instruments at Jantar Mantars, including the Vrihat Samrat Yantra in Jaipur, the world’s largest stone sundial.
About:
- It is a “Polar Sundial with Analemmatic Correction”, which accurately gives the Indian Standard Time (IST) as well as the date.
- Its unique design enables simultaneous time and date reading throughout the year using a single dial and pointer.
- Typical sundials show only local time, which can differ from standard clock time. To match the Indian Standard Time (IST), a correction is applied to account for the sun’s seasonal motion. Two factors cause this variation:
- Earth’s axial tilt (~23.44º) causes the sun to move north-south across the equator.
- Earth’s orbital eccentricity (~0.0167) causes the sun to shift east-west due to changes in Earth’s speed.
- Together, these create a figure-eight pattern in the sun’s path, called the Analemma, leading to the Equation of Time — the difference between solar time and mean clock time.
Features:
- The sundial features a Polar configuration with a 4 ft x 4.2 ft dial plate mounted on an acrylic wedge structure, tilted at 8.53° to match Thumba’s latitude.
- A 1.6 ft tall, 3D-printed model of the RH200 sounding rocket (scaled 1:7.4) is used as the style for casting the shadow, positioned perpendicular to the dial plate.
- The sundial is placed on a 6 ft diameter concrete platform, aligned with the True North-South direction, determined using the Method of Perpendicular Bisectors.
- The sundial’s plate is parallel to the Earth’s polar axis, and the rocket-style shadow caster aligns with the Earth’s equatorial plane, pointing to the celestial equator and local meridian intersection.