1. How far away are the stars?

2. How far away are the stars?
FAR away!

3. Nearest star system: Alpha Centauri
Distance: 4.23 light-years
But how do we
know that?!?
Recall:
1 light-year = 9.5 trillion km

5. BUT: only works out to
about 300 light-years

6. images of Proxima Centauri taken
from Earth and the New Horizons
probe (April 2020)
Proxima Centauri is 4.24 light
years away
New Horizons is currently over 6
billion km away

7. Questions
• Consider the diagram below. Write a simple equation that relates the
distance to a star with an observed parallax of p to our Sun in terms of
astronomical units (the distance between the Earth and Sun).
Remember your trigonometry!
• Imagine a group of astronomers established a colony on Mars.
Compared to scientists back on Earth, would they be more, less, or
equally successfully at estimating stellar distances? Briefly explain your
rationale.