Fluctuations in the Sun’s Apparent Diameter Around 1979

The Sun’s Shifting Size: What’s the Deal with Those Diameter Changes Around 1979?

The Sun. It’s always there, right? Constant, reliable… well, not exactly. Turns out, our star is a bit of a shape-shifter, with properties that wobble and change over time. One of the most intriguing of these is the Sun’s apparent diameter – how big it looks from here on Earth. And back around 1979, some pretty interesting observations kicked off a real debate about whether the Sun was actually shrinking, growing, or just playing tricks on us.

A Look Back: Measuring the Sun Through History

People have been trying to measure the Sun’s size for ages. The ancient Greeks gave it a shot, but things got serious in the 1600s when telescopes came along. Then, in 1979, a study dropped a bombshell. Eddy and Boornazian, digging through old records from the Royal Greenwich Observatory (going all the way back to 1836!), found evidence that the Sun’s horizontal diameter seemed to be shrinking – and fast, like more than 2 arcseconds per century! That’s way faster than anyone expected. What’s more, the vertical diameter wasn’t changing as much, suggesting the Sun was getting a bit… squashed.

This discovery sent shockwaves through the solar physics community. Suddenly, everyone was scrambling to confirm or deny these findings. New instruments were built, old data was re-analyzed. The High Altitude Observatory even created a special telescope, the Solar Diameter Monitor, just to keep an eye on the Sun’s size. Talk about dedication!

Eclipses: Nature’s Measuring Stick

Total solar eclipses are like the universe’s way of giving us a free measuring tool. When the Moon perfectly blocks the Sun, we can get a really good fix on its size. The eclipse of February 26, 1979, was a big one, visible across North America. By comparing observations from that eclipse with those from a 1925 eclipse, some scientists thought the Sun looked bigger back then – about 0.5 arcseconds bigger, which translates to a whopping 375 kilometers! But, as with most things in science, the devil was in the details. Depending on which observations you looked at, the results varied. It made you wonder if we really knew the Moon’s shape as well as we thought we did.

So, What Was Going On? Theories and Headaches

The apparent shrinking Sun of the late 70s led to all sorts of theories, some more plausible than others. Could it be linked to solar activity? Maybe the Sun shrinks when it’s more active? Some researchers thought so. Others, after crunching centuries of data, found no change in the Sun’s size at all.

Honestly, measuring the Sun from the ground is a pain. Our atmosphere distorts everything, like looking through a wavy window. Plus, instruments aren’t perfect, and even the most careful observer can make mistakes. Space-based telescopes like SOHO and SDO give us a much clearer view, but even they have their limits.

Let’s not forget that the Sun itself is a dynamic, boiling ball of gas. It’s not a perfect sphere, it rotates unevenly, and its surface is constantly churning. All this activity can mess with our measurements, making it hard to separate long-term trends from short-term wiggles.

Where Are We Now? The Modern Perspective

Okay, so the idea of the Sun dramatically shrinking, as suggested back in 1979, isn’t really the consensus anymore. But the possibility of subtle changes in the Sun’s diameter is still on the table. Modern measurements suggest the Sun’s size might vary by a few tenths of an arcsecond over time. That might not sound like much, but it could be connected to the solar cycle, magnetic activity, or other internal processes we don’t fully understand yet.

Why does all this matter? Well, understanding the Sun’s diameter fluctuations could unlock secrets about how the Sun works, how stars evolve, and even how the Earth’s climate is affected. By continuing to watch the Sun closely, we hope to unravel more of its mysteries and better understand its place in our solar system. It’s a long game, but one worth playing.