When Albert Einstein proposed his theory of general relativity in 1916, one of his predictions was that light could be deflected by the mass of a nearby object. In 1919 Arthur Eddington took a trip to Principe and photographed stars during a total eclipse. The results confirmed Einstein’s theory.
Cosmic Latte
At the turn of the 21st century, the Anglo-Australian Observatory made a large survey of galaxies in our universe, known as the 2-degree-field galaxy redshift survey (2dFGRS). It measured the spectra and redshifts of more than 230,000 galaxies. The main goal of the survey was to determine the distribution of galaxies within a radius of about 4 billion light years. A statistical analysis of this distribution could then be used to put constraints on things like dark matter and neutrino mass (which I’ll talk about another day).
Slow Down, You Move Too Fast
The cosmic microwave background (CMB) is the faint glow of the primordial fireball known as the big bang. It is often portrayed as existing at the most distant edge of the observable universe, but in fact the entire universe is filled with a sea of photons from the CMB. These photons interact with objects in the universe. In some cases they can interact quite strongly.
Not So Random
Gamma ray bursts (GRBs) are brief, intense bursts of gamma rays. They were first detected in the 1960s as part of a project to observe nuclear weapons tests (http://goo.gl/U9Qbu3). Since then we’ve been able to observe lots of gamma ray bursts, as they occur at a rate of about once a day. We aren’t entirely sure what causes them. One idea is that they occur when a hypergiant star collapses into a black hole. If that were the case, then we would likely see bursts come from random directions (if they originate from outside our galaxy) or along the galactic plane (if they originate in our own galaxy). But now a new study has shown that neither is the case.
Where Are You?
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.