• Think of a road trip! When in a moving car, nearby trees seem to move faster than distant mountains. This change in position due to the observer's movement is called parallax.
• Now, imagine the same on a cosmic level. The Earth orbits the Sun. As it moves, nearby stars appear to move against the backdrop of distant stars.
• Stellar parallax = movement of close stars relative to distant ones due to Earth's orbit.

• Use Earth’s orbit as the baseline (that's a massive 2 Astronomical Units!).
• Measure the angle between the close star and baseline at two times: 6 months apart (e.g., January and July).
• The actual angle (p) = half of the total angle between the star's two positions.
• But! Space angles are so tiny. Instead of degrees, astronomers use
• 1° = 60 arcminutes = 3600 arcseconds.
• Calculate distance (d) to the star using: d = \(\frac 1p\)​ (p in arcseconds and d in parsec).

🌟 Example: If a star's position appears to shift by 0.5 arcseconds over 6 months, its distance would be about 2 parsecs from us.

• Problem: Earth’s atmosphere distorts starlight, making accurate measurements tough.
• Solution: Send telescopes to space! 🚀
  • E.g., The Gaia satellite. Launched in 2013, it's set to map a billion stars in 3D until 2025.
  • With a resolution of 7µ arcseconds, Gaia can measure stars up to 100,000 parsecs away!

• 3D star mapping: Not just our Milky Way, but stars in the Local Group galaxies.
• Test Einstein’s general theory of relativity. (Go, Einstein! 🎉)
• Study planets outside our Solar System.

FYI: Space missions = pricey 💰. That's why countries team up, showcasing the power of collaboration in science and engineering!