Astronomy and Cosmology

Tools of the trade – Instruments

The difference between astronomy and other sciences is that with astronomy, you cannot hold in your hands what you want to study. There are exceptions of course, because there are meteorites, moon rocks, and the evidence from space probes, but for the most part, evidence is indirect when it comes to galaxies, stars, planets, and asteroids.

Most of the evidence comes from telescopes that use the electromagnetic spectrum which is composed of several forms of electromagnetic energy or electromagnetic waves:

• Visible light – The form of electromagnetic waves that can be detected by the human eye. Using telescopes that reflect and refract light, astronomers have produced most images from ground and space based telescopes. Charge coupled devices (CCD’s) revolutionized these observations.
• Radio waves – Radio telescopes are large radio receivers that look somewhat like large satellite TV antennas and they are designed to receive radio waves from astronomical objects. In New Mexico is one of the world’s premiere radio astronomical observatories, the VLA, which stands for the “very large array.” There are 27 dishes, each measuring twenty five meters across and mounted on railroad tracks.
• Ultraviolet – Since the atmosphere filters out most of the UV spectrum, these instruments have to be above the atmosphere in satellites containing ultraviolet telescopes.
• Infrared (heat) – Special detectors designed to detect infrared radiation can be mounted on optical telescopes, which then become infrared telescopes. They can be ground or space based.
• X-rays and gamma rays – There are no ground based instruments because the atmosphere filters even more x-rays than UV. X-ray and gamma ray observations must be done from space.

All forms of electromagnetic waves travel at a rate of 300,000 km/s (or 186,000 miles per second). At that rate, light can make 7 trips around the equator of the earth in one second. Light defines distance in space units: a light year is the distance light travels in one year. The closest star (besides our sun) is Proxima Centauri – 4.3 light years away (or 26 trillion miles).

Cosmology is the scientific study of the origin and evolution of the Universe. Evidence suggests that the universe began with a big bang. Edwin Hubble’s 1929 observation that galaxies were moving away from us provided the first clue that led to the Big Bang theory. Many other observations since confirm this.

The Big Bang theory predicts that the light elements (hydrogen, helium, lithium, and beryllium) were fused from protons and neutrons in the first few minutes after the Big Bang because of the intense heat. These elements are abundant throughout the universe. Heavier elements are all synthesized in stars. As stars die, they turn helium into carbon, oxygen, silicon, sulfur, and iron. Heavier elements are produced and blasted back into space through supernova explosions.

The early universe was very hot. The cosmic microwave background radiation is thought to be the remnant heat leftover from the Big Bang.

Universal Age

Various astronomers estimate that the Big Bang occurred between 12 and 24 billion years ago. This number varies by source because of the error that must be considered with the method of calculation. The most recent estimates are closer to 12 or 13 billion years. For comparison:

• Solar System is thought to be about 4.5 billion years old
• Humans have existed for 1 or 2 million years.

Astronomers estimate the age of the universe by:

• Measuring the rate of expansion of the universe to see when it began as a single mass
• Looking for the oldest stars
• Using methods that compare the rate of decay of known radiometric substances

Our sun, solar system, and planets

All the planets orbit the sun in the same directions and on almost the same plane which suggests a common origin. The system has a counter-clockwise spin as observed from the north side of the solar system according to the way the North Pole of the Earth points.

Because the weight of an object depends on the mass of a planet and the gravitational attraction of that planet, an interesting exercise is to imagine what your weight would be on another planet. Using the gravitational factor from the table below you can see how much this can vary. If you weigh 120 lb on Earth, on Mercury you would weigh 120 lb · 0.38 , or 46 lb. On Neptune, you would weigh 120 lb · 1.2, or 144 lb.

Now consider that your age depends on the number of Earth years that have passed, but a year on another planet is not the same length of time as it is on Earth. To find your age according to the length of another planet’s year, divide your age in Earth years by the period of revolution (in Earth years) of the planet listed in the table below. If you are 47 Earth years old, on Mercury you would be 47 years ÷ 0.241, or 195 Mercury years old. On Neptune’s orbit, you would be 47 years ÷ 164.8, or 0.285 years old. That is only 3 and a half Neptunian months old! The phrase “you can never be too slim or too young” takes on a whole new meaning, but it may not be worth moving to Mercury or Neptune!