Zero Shadow Day

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• COSMOS Observation: The Cosmology Education and Research Training Center (COSMOS), Mysuru, under the Indian Institute of Astrophysics, recently observed Zero Shadow Day (ZSD), a rare celestial event where vertical objects cast no shadows. This initiative aims to promote public awareness of astronomy and Earth’s orbital dynamics.

About Zero Shadow Day

• Definition: A celestial phenomenon where the Sun is directly overhead, causing vertical objects (e.g., poles, people) to cast no shadows.

• Cause: Occurs due to Earth’s 23.5° axial tilt and its orbit around the Sun, altering the Sun’s apparent position relative to Earth’s surface.

• Key Condition:

  • Declination = Latitude: The Sun’s declination (angular distance from the celestial equator) matches the observer’s latitude.

Key Features

1. Frequency:

   • Twice a Year: Observed in regions between the Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S).

   • Timing:

     • Uttarayan (Sun’s northward movement): ~April–May in northern tropics.

     • Dakshinayan (Sun’s southward movement): ~July–August in southern tropics.

   • Duration: Exact “zero shadow” lasts a fraction of a second, but the effect is visible for 1–1.5 minutes.

2. Geographic Scope:

   • India: Southern regions below ~23.5°N latitude (e.g., Karnataka, Tamil Nadu, Kerala, Telangana, Maharashtra, Odisha).

   • Global: All tropical zones (e.g., Mexico, Brazil, Indonesia, northern Australia).

3. Scientific Significance:

   • Demonstrates Earth’s axial tilt and orbital mechanics.

   • Used in astronomy education to explain solstices, equinoxes, and seasonal changes.

Regions Experiencing ZSD in India

• States/UTs:

  • Southern India: Kerala, Tamil Nadu, Karnataka, Andhra Pradesh, Telangana.

  • Western India: Goa, Maharashtra, Gujarat (south).

  • Eastern India: Odisha, West Bengal (south), Chhattisgarh.

  • UTs: Andaman & Nicobar, Puducherry, Dadra & Nagar Haveli, Daman & Diu.

Key Takeaways

• Celestial Marvel: ZSD highlights the interplay of Earth’s tilt and orbit, offering a tangible lesson in astronomy.

• Educational Tool: Events like COSMOS’s observation drive public engagement in science.

• Tropical Phenomenon: Limited to regions between the Tropics, making it a unique experience for residents and tourists.

• Cultural Relevance: Linked to traditional solar calendars in tropical cultures.

FAQs

1. What is Zero Shadow Day?

   • Ans: A day when the Sun is directly overhead, causing vertical objects to cast no shadow.

2. Between which latitudes does ZSD occur?

   • Ans: Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S).

3. How many times does ZSD occur annually at a location?

   • Ans: Twice (once during Uttarayan and once during Dakshinayan).