The seven main types are M, K, G, F, A, B and O. M stars are the coldest stars and O stars are the hottest.

## What are the three main luminosity classes?

Luminosity Classes
II Bright Giants Canopus (F0II)
III Giants Capella (G5III)
IV Subgiants Beta Cru (B0IV)
V Main Sequence Vega (A0V)

## How is luminosity class determined?

In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star’s spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs.

## How does knowing the distance help classify a star?

A star is classified by luminosity and color. luminosity is measure in magnitudes and color is measured by temperature. For example, if the star is relatively close to us, we can determine its distance using stellar parallax: By measuring the shift angle seen from Earth, we can determine distance.

## What can you tell about a star from its brightness?

The total energy emitted per second by a star is called its luminosity. The apparent brightness of a star depends on both its luminosity and its distance from Earth. Thus, the determination of apparent brightness and measurement of the distance to a star provide enough information to calculate its luminosity.

## Does luminance change with distance?

And Luminance is a property of a light source; so it does not vary at all, with distance from the light source. Now if you meant “Illuminance” or illumination instead of luminance, then that falls off with the inverse square of the distance, and is the lumens per square meter, or “lux” falling on a distant surface.

## What is the relationship between luminosity brightness and distance?

Brightness-Luminosity Relationship: At a particular Luminosity, the more distant an object is, the fainter its apparent brightness becomes as the square of the distance.

## Which planets are visible in the sky tonight?

Four planets will be visible to the naked eye while the New Moon sits in darkness. Tonight’s sky will boast clearly visible Venus, Mars, Jupiter, and Saturn. Meanwhile, Mercury, Uranus, and Neptune will be visible but you will likely need some sort of telescope to aid in viewing those three planets.