Greetings, stargazers.
Spring is galaxy season for many amateur astronomers. However, when looking through an eyepiece instead of a camera for astrophotography, you might think of this as the season of pale gray smudges that go along with the pale white dots of the much closer stars.
Just as with star colors, seeing colors of galaxies is more a limitation of human eyes. If our eyes were more sensitive to dim light, we could more easily differentiate the young, hot, blue stars from the cooler red ones. There are very few stars that are bright enough to distinguish colors, but the contrast in Orion between Betelgeuse (red) and Rigel (blue) is one of the best examples of seeing color differences in stars.
A star’s color is directly related to the temperature of the surface of that star. Red for the cooler stars and blue for the hotter ones. Wilhelm Wien derived this relationship in 1893, and it was one of the important precursors leading toward quantum mechanics in the 20th century.
Stars that appear red are actually radiating most of their energy in the infrared part of the spectrum, which our eyes have a hard time detecting. Blue stars are emitting most of their radiation in the ultraviolet. What we call white light is just that midway point where the radiation peak is in the middle of the visible spectrum. The reason our eyes are sensitive to this part of the spectrum is simply because that is what the sun is radiating the most.
Today, the effective color of LED light bulbs is described using their equivalent temperature. This is only place I know where the Kelvin temperature scale is widely used by nonscientists. Daylight-white bulbs are those listed around 6,000 Kelvin, and that is close to the temperature of the surface of the sun.
Useful links
Wien’s Law
Cancer constellation
Comet SWAN
Astronomy picture of the day
An Astronomer’s forecast for Durango
Old Fort Lewis Observatory
http://www.fortlewis.edu/observatory
hakes_c@fortlewis.edu
Spring is not only the season of weather transitions, but also of changing constellations. The bright constellations of the winter hexagon surrounding Orion are setting in the west in the early evening. After Orion sets, his archenemy Scorpius rises in the east soon after midnight. After Scorpius rises, the summer Milky Way and all its associated constellations soon follow.
Jupiter is in the western sky near some of the more colorful stars. It is in Taurus, above the bright star Aldebaran and to the right of the red giant Betelgeuse. Mars is a bit higher, near the twins Castor and Pollux in Gemini.
To the east of Mars and Gemini is the much dimmer constellation, Cancer. Cancer is the home of M44, also known as Praesepe, or the Beehive cluster. This open cluster is one of the closer ones to the solar system, approximately 600 light-years away. It can be seen with the naked eye as a dim fuzzy patch, and is exceptionally rewarding when viewed through binoculars, as you can easily see many of the about 1,000 stars.
Another newly-discovered comet, C/2025 F2 (SWAN), is moving through the constellation Pegasus in the morning eastern sky just before dawn. Right now it is only visible though telescopes. However, it should make its closest approach to the sun on May 1, and might become visible to the naked eye in the evening sky then.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.
