One of the most basic skills in astronomy is know how to find objects in the night sky. That means you need a way to navigate the sky. The simplest way is known as altitude and azimuth. Starting at due north, rotate clockwise along the horizon until you are directly under the star you want, then move above the horizon to reach your star. It is a simple coordinate system, since it is just so many degrees clockwise (azimuth) and so many degrees upward (altitude).
Metonic Moon
Today the Moon is in its New Moon phase. This won’t happen again for another 19 years. Actually that isn’t quite true. It takes about 29.5 days for the Moon to go from one new moon phase to the next, so we’ll have a new moon roughly once a month, just like always, but there is a periodicity to moon phases that spans 19 years, and it is known as the Metonic cycle.
Rainbow Star
When we view stars from the surface of our planet, they appear to twinkle. This is due to turbulence in the air, which creates air fluctuations that cause the starlight to deflect slightly. Since stars appear point-like due to their distance, the small deflections are enough to cause the star to twinkle.
Usually we just notice the variation in brightness, but air also acts like a prism, bending different colors of light by different amounts. So not only do stars appear to vary in brightness, they can also appear to vary in color.
In the Deep Midwinter
Today is Winter Solstice, which marks the beginning of Winter for those in the southern hemisphere. On this day the sun follows its lowest path in the sky, rising later and setting earlier than any other day of the year. Starting tomorrow the Sun will trace a higher and higher daily path until it reaches the Summer Solstice in December. Of course most people live in the northern hemisphere, and for them today marks the Summer Solstice. Contrary to popular belief, the seasons are not caused by our distance from the Sun. The Earth is actually closest to the Sun (at perihelion) on January 3, and farthest (at aphelion) on July 4. Although the changing distance from the Sun does have an effect on the Earth’s temperature, it is tiny when compared to the variation of the Sun’s path across the sky. It is our orientation relative to the sun, not our distance, which is the cause of our seasons.
Size Matters
With the recent post on Pluto, one of the questions that came up was about imaging Pluto itself. Currently the best image we have of Pluto is one taken by the Hubble telescope. It is a blurry smudge of shading without any real detail. At the same time, Hubble has taken extremely detailed images of distant objects, such as the ultra deep field. So how is it that Hubble can image distant galaxies in detail, but can’t get a detailed image of Pluto? It all comes down to an object’s size. Not its actual size, but its apparent size.
Father and Son
William Herschel was an astronomer of the 1700s and early 1800s. He is most famous for his discovery of the planet Uranus. But Herschel made several other important discoveries, including work on double stars, showing that some of them (what we now call binary stars) orbited each other under gravitational attraction. He also discovered infrared light, by passing sunlight through a prism, holding a thermometer just beyond the red light of the spectrum, and demonstrating that the thermometer was heated by in invisible light we now call infrared. He was the father of one son, John.
Kepler’s Hypothesis
One of the common misconceptions presented in science is that it occurs in revolutionary steps. For example, the idea that Copernicus developed the heliocentric (sun-centered) model of the solar system, then Kepler showed that planets moved in ellipses and introduced Kepler’s laws, then Newton introduced the law of gravity that proved Kepler’s laws to be true. Each revolutionary idea replacing the previous one. But the real history is not quite so clean. Take for instance the development of Kepler’s laws.
Under the Lens
Proxima Centauri is the closest star (excepting the Sun) to Earth. It is a red dwarf a bit more than a tenth the mass of our Sun, and about four light years away. We don’t know if it has any planets, but that may change in a few years due to a fortunate alignment.
Dark of Night
When you look up in the night sky, there are areas of the sky that appear dark. That’s because there is nothing in that region bright enough for us to see with the naked eye. If you looked upon this region with a telescope, you would find dim stars and galaxies, but you would still see areas that appeared dark to you. How far could you take this? If you kept looking at smaller and smaller dark regions with ever more powerful telescopes, what would you see?