Which magnitude describes the brightest star

Now decide how bright your target star is when compared to the two comparison stars. Is it halfway between them, or is it somewhere else in between, being of a more similar brightness to one than the other? Use your own judgement and be consistent in how you make your comparisons. Look up the magnitudes of the comparison stars on your star chart. Anton Vamplew is an amateur astronomer, author and lecturer. The stars of the Summer Triangle asterism.

Star Vega is top left. Altair can be seen below in the middle and Deneb is far left. Credit: A. Light-sensitive charged-coupled devices CCDs inside digital cameras measure the amount of light coming from stars, and can provide a more precise definition of brightness.

Using this scale, astronomers now define five magnitudes' difference as having a brightness ratio of Vega was used as the reference star for the scale. Initially it had a magnitude of 0, but more precise instrumentation changed that to 0. When taking Earth as a reference point, however, the scale of magnitude fails to account for the true differences in brightness between stars.

The apparent brightness, or apparent magnitude, depends on the location of the observer. Different observers will come up with a different measurement, depending on their locations and distance from the star. Stars that are closer to Earth, but fainter, could appear brighter than far more luminous ones that are far away. The solution was to implement an absolute magnitude scale to provide a reference between stars. To do so, astronomers calculate the brightness of stars as they would appear if it were Another measure of brightness is luminosity, which is the power of a star — the amount of energy light that a star emits from its surface.

It is usually expressed in watts and measured in terms of the luminosity of the sun. For example, the sun's luminosity is trillion trillion watts. It has also been calculated that the human eye perceives a one magnitude change as being 2. Therefore a difference of 5 magnitudes has been defined as being equal to a factor of exactly in apparent brightness.

It follows that one magnitude is equal to the fifth root of , or approximately 2. For example, Venus and Sirius have a difference of about 3 magnitudes.

This means that Venus appears 2. In other words, it would take 15 stars with the brightness of Sirius in one spot in the sky to equal the brightness of Venus. Mars at brightest. Sirius brightest star.

Naked eye limit in an urban neighborhood. Uranus at brightest. Naked eye limit.