Saturday, April 25, 2015

Tonight's Sky for April 25: Astronomy Day/First Quarter Moon

Today marks a little known holiday: International Astronomy Day, which began as a 1-club event and eventually spread to encompass the entire world.
With humble origins as an attempt at public outreach by the Astronomical Association of Southern California, the effort to bring astronomy to the masses, often city dwellers, quickly grew in popularity to the point where the holiday eventually went national, and then international. Now, over 40 years after the first Astronomy Day (1973) the holiday continues to grow and become more relevant.

Why the part about being relevant? Simple: dark skies are going away fast.

When the first Astronomy Day was launched in 1973, the whole idea was to set up telescopes in public places where astronomers could show members of the general public the wonders of the universe. Naturally, to guarantee that the public would show up, the telescopes had to be set up in urban/suburban locations, areas that are not all that good for astronomy. Obviously, by looking at the success of the holiday, people are seeing things in the telescopes.

Lesson of the day: you can do astronomy from just about anywhere.

For starters, Astronomy Day is always coordinated to coincide as best possible with First Quarter Moon as it is always visible as it is the second brightest thing in the sky after the Sun. Believe it or not, there are astronomers who spend the majority of their telescope time studying the Moon. Second, planets. All of the planets are generally of 0 magnitude or brighter, thus visible from all but the most light polluted areas. Being bright targets, the planets are also good targets for examination by city-dwellers. For suburbanites, binary (double, triple, etc.) stars are also a lot of fun to look at because they, too, can be observed in all but the worst of lighting conditions.


So yes, the dark skies are going away more every year but, if you know what to look for and are content with the fact that you may not be able to see deep sky nebulae, galaxies, and clusters from your backyard, there is plenty of fun to be had with a telescope in a city.

On top of the festivities, the Moon, second brightest object in the sky, has reached the First Quarter phase, which means that it is exactly 90 degrees around its orbit of Earth and is one quarter finished with its current orbit..

As for lunar mechanics, the Moon is always half lit. The reason we don't always see it as such is thanks to orientation in relation to us. Right now, with the Moon at a 90 degree angle relative to the Earth-Sun line, we only see half of the lit side.

After today, we will see more of the Moon each night as its lit side turns more toward from us and heads toward Full in a week.

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