Astronomers classify elliptical galaxies by

a. the number of stars they contain
b. their colors
c. how flattened they appear
d. their diameters

Astronomers classify galaxies according to Hubble's classification into elliptical, spiral and irregular, being the first two classes the most frequent.  

In the specific case of Elliptical galaxies, their main characteristic is that the concentration of stars decreases from the nucleus, which is small and very bright, towards its edges. In addition, they contain a large population of old stars, usually little gas and dust, and some newly formed stars.  

They are subdivided into eight classes, from E0 with zero eccentricity (spherical) to E7 (called husiform).  

However, it should be noted that this classification is based only on the visual appearance of the galaxy, and does not take into account other aspects, such as the rate of star formation or the activity of the galactic nucleus.  

Therefore, astronomer's clasification for elliptical galaxies is by their shape, which in this case is how flattened they appear.

a maximum–minimum thermometer. the scales are fahrenheit on the inside of the u and celsius on the outside. the current temperature is 23 degrees celsius, the maximum recorded is 25, and the minimum is 15, both read from the base of the small markers in each arm of the u tube. the bulbs are hidden by a plastic housing.

six's thermometer is a registering thermometer which can record the maximum and minimum temperatures reached over a period of time, for example 24 hours. it is used to record the extremes of temperature at a location, for instance in meteorology and horticulture. it was invented by a british scientist james six, born in canterbury, in 1780; [1] the same basic design remains in use.

it is also commonly known as a maximum–minimum, minimum–maximum, maxima–minima or minima–maxima thermometer, of which it is the earliest practical design.

the thermometer indicates the current temperature, and the highest and lowest temperatures since last reset.