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# Cosmic distance ladder : The size of the Sun! How about ... the sun. Can we estimate its size ? As it turns out, during a solar eclipse the moon blocks out the sun almost completely, where the moon overlaps the sun nearly perfectly. Here is an image of the 1999 solar eclipse, taken from Wikipedia: ![[1 teaching/summer program 2023/week 1/---files/Pasted image 20230511104721.png]] This shows **the apparent sizes** of the sun and moon are **approximately the same** from an Earth observer. By the way, ![[---images/---assets/---icons/important-icon.svg]] **never look at the sun directly** ![[---images/---assets/---icons/important-icon.svg]] even at an eclipse event! ![[---images/---assets/---icons/question-icon.svg]] Of course the moon and sun do not have the same size. But using the fact that they look apparently the same from an Earth perspective, **draw in a circle representing the sun** in the following diagram: ![[1 teaching/summer program 2023/week 1/---files/Cosmic_distance_ladder_5 2023-05-11 11.26.05.excalidraw.svg]] %%[[1 teaching/summer program 2023/week 1/---files/Cosmic_distance_ladder_5 2023-05-11 11.26.05.excalidraw|🖋 Edit in Excalidraw]], and the [[summer program 2023/week 1/---files/Cosmic_distance_ladder_5 2023-05-11 11.26.05.excalidraw.dark.svg|dark exported image]]%% ![[---images/---assets/---icons/question-icon.svg]] Now, use your diagram to **find the radius of the sun** ! Hint we already found the radius of the moon $R_\text{moon}$, the distance to the moon $d_\text{moon}$, as well as the distance to the sun $d_\text{sun}$. Compare your answer from what you found from the internet. If instead you use the actual values to find the radius of the sun, how much better is the estimate? ![[---images/---assets/---icons/question-icon.svg]] This whole endeavor is called the **cosmic distance ladder** because we use established astrometric quantities to estimate the next one, and so on. What are some considerations we need to be concern with if we estimate quantities this way?