On learning about space
- Celestial Cat
- Nov 3, 2019
- 5 min read
Updated: Apr 2, 2022
Space science can be an intimidating subject to get into based on the sheer scale alone. For as intimidating as mentally conquering the universe may be, it is also an incredibly satisfying achievement. If you’re interested in the universe, chances are you are wondering what's out there. This is a good question because at first, it is not very clear what heavenly bodies lie hidden in our sky. To keep track of any given celestial object we will require the use of astronomical catalogs. There is a slew of many catalogs, each one lists astronomical items with some common denominator among them. Some are collections of objects observed by the same telescope while others are objects cataloged by a single individual; usually a historical figure. This is the case for the Messier catalog, which was an attempt to list all known objects that were not comets. Many of these were nebula; some of the more visually appealing objects in the universe. Learning how scientific discoveries occurred historically (and what experiments lead to the discovery) can help the brain rationalize how we know what we know, and how that has affected human thought sense.
One main point of interest for those who want to tame the universe is to learn celestial distances. It is hard to appreciate the scale of any astronomical fact without first familiarizing yourself with the cosmic ruler. For example, you could learn that Gliese 182 is 16 light-years away [1]. However, without an awareness of distance, this star could be anywhere in the universe. One wouldn’t even know if this lied inside or outside of our galaxy (it’s inside). There are a few formats of distances that are useful depending on the scale.
One of which is called the astronomical unit (AU).This is the distance between Earth and the Sun (149,597,870,691 miles or 149.6 million km). An AU is good for measuring distances within our solar system. The orbit of Mars is about a half of an AU away while Venus, in the other direction, is .3 astronomical units away. Jupiter is 4.2 AUs followed by Saturn which sits eight and a half AUs away from Earth. Uranus and Neptune follow with distances of 18.18 and 29 AUs respectively. Dwarf planet Pluto is 38.44 AUs away from Earth. Beyond Pluto lies a sphere of comets around the sun, called the Ortt cloud, which begins at 3,000 AU and ends at 135,000 AU [2].
Another important measure of distance is the “light year”. This is the distance light travels in one year ( 63,240 AU). The closest star, Alpha Centauri, is 4.2 light-years away [3]. Perhaps a lonely perspective emerges on the density of the universe when one considers that light is the fastest thing in the universe. For reference, the center of the milky way galaxy is 30,000 light-years away from the sun. The outer edge of the galaxy is 20,000 light-years, placing the orbit of the sun at roughly in the middle of the galaxy’s radius. It is worth noting that the accuracy of distances gets rougher the further one travels out. Though, at such incomprehensible distances, it doesn’t make much of a difference if we are off by a few light-years. The next closest object of significance would be the dwarf galaxies of the Magellanic clouds sitting 160,000 light-years away. Next would be the Andromeda galaxy at 2 million light-years which is also one of the furthest objects in the sky that’s visible to the naked eye [2].
The sky projects itself to us as a half-cut sphere and so can be measured in degrees. A neat trick to navigate your way through the constellations is to hold your hand out at arm's length and allow your body's natural proportions to guide the measurements of the heavens. As shown above, various parts of your hand can be used to determine the distance between objects in the sky by any amount of degrees.
It is, of course, necessary to learn the constellations so that it is easy to find various space phenomena. This can be practiced with free software such as Stellarium. Probing further into the universe brings forth the measurement of the arcminute which is measured as 1/60th of a degree. An arcsecond goes another step deeper, measuring at 1/60th of an arcminute. This connects to the measurement of the parsec which equals 3.26 light-years. When the Earth looks onto a star from one side of the sun, the position of that star can shift while viewing it on the other side of the sun. This is called parallax. If the distance that the star shifts from moving a distance of one AU equals one arcsecond then that defines the distance as a parsec. This is more mathematically useful than other measurements because it allows trigonometry to be accessible as the star, Earth and Sun make a right angle. With this method, you can mount the jaws of the universe and plunge further down the throat of the infinity that swallows the sky.
As you go further out into the universe you will require to stack multiples of parsecs. A megaparsec (Mpc), for example, equals one million parsecs. A gigaparsec (Gps) is a billion. The Local Group is a collection of about 40 galaxies that surround our Milkyway. It spans 10 million light-years or roughly three megaparsecs [4]. Going a step further reveals the Virgo supercluster consisting of over 40,000 galaxies which is 100 million light-years in diameter, or roughly 30 Mpc [5]. The Laniakea supercluster is a whopping 160 Mpc [6]. This keeps going until we finally arrive at the edge of the observable universe which is 28 gigaparsecs or 93 billion light-years [7].
Distances should not be the only measurement that warrants awareness. It’s also useful to be familiar with cosmic measurements of time. The big bang occurred 13.7 billion years ago [8]. A few hundred million years after would see the forming of stars and early galaxies. 4.5 billion years ago saw the creation of our solar system, which would see the emergence of life only a billion years later [9] [10]. Space and time are essential concepts for any space enthusiast to understand. However, those who are especially curious may become familiar with all possible measurements of physical properties to appreciate the full scale of the universe. The physics of temperature, velocity, mass and everything in between becomes more apparent with time and practice. These properties are the windows through which we are able to peak beyond the reality presented to us by our meager five senses.
Glossary
Arcminute
One sixtieth of a degree of angular measure. The Moon is 31 arcminutes across.
Arcsecond
One sixtieth of an arcminute, or 1/3600 of a degree. Jupiter is 40 arcseconds across.
Astronomical Unit
Mean distance between the Earth and the Sun: 149,598,500km.
Messier Catalogue One of the earliest catalogues of nebulous-appearing astronomical objects, compiled in 1781 by the French astronomer Charles Messier. Messier's catalogue included many objects that were later realized to be galaxies.
Parallax
The tiny shift in a star's apparent position that occurs when the star is viewed from slightly different perspectives as the Earth revolves around the Sun. The larger a star's parallax, the closer the star is to Earth.
Parsec
The distance at which one astronomical unit subtends an angle of 1 second of arc. 1 pc = 206,265 AU = 3.086 × 1013 km = 3.26 light-years.
*All definitions provided by ned.ipac.caltech; a NASA-funded database of astronomical information and definitions based at the California Institute of Technology.
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