Steve’s Virtual Planet

Magnitude? Yes! (apparently)

Yes, indeed! Apparently! That’s how we see a star’s brightness form our perspective here on Earth. We use the term “magnitude” to describe the brightness of a star. We call the measurement of the brightness from Earth the “apparent magnitude“. The effect of this apparent brightness leads us to the more exacting method of using a numbered scale to quantify what we see. And this scale goes all the way back to the days of ancient Greece and is credited to a very clever mathematician named Hipparchus.

Hipparchus came up with a six level scale based on naked eye brightness that is still largely the same today. In this scale, the number 1 is given to the brightest stars, with a gradual decrease in brightness shown with a higher number from 2 to 6. Yes, the number gets higher as the stars gets dimmer. It’s a purely arbitrary system that has been the convention since about 150 BC.

When you use a typical sky map or star chart, look for the legend that shows a row of different diameter dots with a set of numbers on them. SkyMap uses a scale from -1 to 4 for its range. Other maps sometimes extend the range down to 6 or 7.

In one of my earlier posts, I examined several properties of stars such as mass and size. I will leave that line of research to you but it does have some relation to the topic at hand. However, from a star gazer’s perspective, we don’t have to delve too deep into astrophysics to work with this brightness scale. The value for apparent magnitude is found in star charts and tables of the stars as well. In some cases it is otherwise listed as “visual magnitude”, which means the same thing.

In any case, stellar brightness from -1 down to about 4 is the typical range in the suburbs. If you’re out in the country and have a really dark site, you will likely get down to around 6 magnitude, perhaps even to 6.5. And don’t forget to get your eyes adapted to the darker conditions for a better experience looking for these dimmer objects.