The diameter of the Sun is about 400 times larger than the diameter of the Moon. The Moon is about 389 times closer to the Earth than the Sun. This means that the size of the Sun and Moon in the sky are about the same, and that happy coincidence is what allows us to have the greatest show on Earth: the solar eclipse.
Warped Astronomy
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).
Moons of Galileo
In the first few months of 1610, Galileo Galilei pointed a small twenty-power telescope at Jupiter. What he observed changed the way we understood the universe.
With his telescope, Galileo saw what appeared to be three faint stars in a straight line near Jupiter. The next evening he saw what appeared to be the same three stars, but it seemed Jupiter had moved in the opposite direction to its expected motion. Within a few days it became clear that Galileo wasn’t observing the motion of Jupiter relative to some faint stars, but rather these stars were moving along with Jupiter.
Galaxy Rangers
In an earlier post I wrote about one of the mysteries of dark matter. While dark matter matches most observations very well, it doesn’t do well in the area of dwarf galaxies. In particular, computer simulations predict that there should be many more dwarf galaxies than we observe. This has been taken to mean that either the simulations are somehow flawed, or dark matter isn’t the complete solution we’ve thought. But now new research has found that dark matter simulations might be right after all.
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.
Missing Mass Mystery
This year data from the Planck satellite released the most precise observations of the cosmic microwave background. The results tell us that about 68.3% of the universe is dark energy, 26.8% is dark matter, and 4.9% is baryonic matter. Baryonic matter is the regular matter that makes up stars and planets and me and you. It is called baryonic because protons and neutrons which form the nuclei of atoms are known as baryons. (There are other, more exotic, baryonic particles, but protons and neutrons are the most common) So all the atoms and molecules we are familiar with are baryonic matter.
Twilight Sparkle
If you live in the United States, you will likely take in an evening of fireworks. While you are enjoying them safely, you’ll notice that fireworks come in a variety of colors. The different colors are due to various metallic salts that are used in the fireworks. For example, reds can be created with strontium or lithium salts, orange with calcium, green with barium, blue with copper, and so on. A wide variety of colors can be produced by mixing these compounds as well.