The Ultimate Guide To The Universe

Nemanja PavlovicNemanja 

Some general facts about the universe

1. Light year is a measure of distance, not time. It is the distance that light travels during one Earth year ( The speed of light is 300,000km/s, which means that this is a very, tremendously, amazingly huge distance of over 9.5 trillion km)

2. AU, or astronomical unit is the distance between the Sun and the Earth, and it measures 8 light minutes and 19 light seconds, or 149.597 million kilometers in humans-can-achieve-it units.

3. To top it off, a unit called parsec is even longer than a light year. Measuring 3.26 light years, it is a function of an astronomical unit and a parallax angle of 1 degree. Its name is derived from “parallax of one arcsecond”

4. The biggest known star currently is UY Scuti, a bright red supergiant, located 9500 light years away in the Scutum constellation. It is more than 1,708 times the size of the Sun.  If UY Scuti was placed in our system instead of the Sun, it would engulf everything up to the orbit of Saturn.

5. The most massive star, and one of the hottest that we know of, is the RMC 136a1, with the mass of 315 Suns and the temperature of over 50000 K! It is just a brisk walk away of 163,000 light-years, sitting in the Large Magellanic cloud.

6. Universe is estimated to be 13.82 billion years old.  Even though we know its age we don’t really know its size since it’s always expanding, so the light actually didn’t have time to reach us yet from the furthest reaches of space.  Current estimates, based on a phenomenon called redshift, are that it is at least 46 billion light years across.

7. Galaxies can collide. In fact, our own milky way is due a collision with Andromeda galaxy. Not to worry though, this is going to happen in over 4 billion years from now, and even when it happens, galactic distances are so vast that the chances of a star or a planet hitting each other are almost non-existent.

8. There are over 100 billion galaxies in the universe, by current estimates made by Hubble space telescope, but that number is probably to rise as we develop better telescope technology.

UPDATE: The newest estimates made by a computer simulation suggest that there are over 500 billion galaxies in the universe!

9. There are over 300 billion stars in our galaxy, the Milky Way. In the observable universe the estimate is that there are 70 billion trillion (7 x 1022) stars. Don’t even try to wrap your head around that number.

10. A popular comparison that can illustrate these numbers is this: There are more stars in the universe than there are grains of sand on all the beaches and deserts on Earth.

11. Milky Way is our home galaxy. It’s a spiral galaxy, with the supermassive black hole in its center and it spans between 100-200 thousand light-years. (It’s kinda hard to measure such distances, so the current estimates are really rough).

12. Milky Way has two major spiral arms that start at the central bar of stars, and slowly taper off. Our Solar system is located in one minor spiral arm called the Orion arm.

13. The biggest galaxy is over 30 times bigger than our own modest Milky Way. The IC 1101 is a supergiant elliptical galaxy and it spans over 5.8 million light years, with more than a 100 trillion stars that call it home.

14. Galaxies come in different sizes, but also different shapes.  The three main types of galaxies are elliptical, spiral and irregular. The Hubble classification is a bit more complex – Elipticals, spirals, lenticulars and irregulars, of which each category has subcategories.

15. The first spiral galaxy we discovered, besides our own, is the Whirlpool Galaxy (M51). It is estimated to be 23 million years away from the Milky Way.

16. Measuring distances to galaxies is tricky. We try to find a single star in that galaxy and measure the distance to it.  If the galaxy is too far away to distinguish individual stars, astronomers find supernovae, which are much brighter than ordinary stars, and measure that distance.

The Solar system facts

17. There are 8 planets in our solar system. In order, from the closest to the Sun to the furthest, they are:  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

18. For a long time the little, distant Pluto was listed as a planet, but it has its own classification now: a dwarf planet.

19. The planets are separated into the planets of the inner solar system, and the outer system. There is a huge difference between these planets, both in their size and their composition. The planets of the outer system are known as the giant planets (or Jovian planets), while the inner planets are called the terrestrial planets.

20. The inner planets are fairly small, with the Earth being the biggest among them. They are pretty dense, with a rocky composition, iron-nickel cores and few or no satellites. Each of these has some sort of surface features, such as impact craters, volcanoes and canyons.

21. Revolution is what we call one complete circle that a planet makes around the Sun, and rotation is a single full circle around the planet’s axis. Earth’s rotation is what we call a day, and its Revolution is one year.

22. Mercury is the planet closest to the Sun. It has a year of 88 days, and a day that lasts almost 60 Earth days. On the side that is facing towards the Sun it has a scorching surface temperature of over 700K (423 C), but on the other side it’s surprisingly freezing with temperatures below 0 C.

23. The reason for this huge temperature difference is because of Mercury’s long day. The dark side is so cold that there are even hints that there might be actual traces of water ice.

24. Even though the Mercury is the planet nearest to the Sun, Venus is actually the hottest. That is because Venus has an extremely dense carbon-dioxide atmosphere, which creates the strongest green-house effect known to man.

25. The pressure on the surface of Venus is as high as it is at the depth of 1 kilometer in Earth’s oceans. The temperature is at least 735 K (462 °C), and its surface features look as what we normally think Hell looks like.

26. The Earth is actually closest to the Sun during January and farthest during July. The seasons we experience are due to the tilt of the Earth’s axis, which makes certain areas get more sunshine at the different parts of its revolution.

27. Earth’s orbit starts at an altitude of 2000 km.  If we were to build a staircase from the sea level to orbit, it would take two weeks to climb.

28. The only natural satellite that orbits the Earth is Moon. It is one of the largest and densest satellites, but it doesn’t have any atmosphere. The Moon is in synchronous orbit around the Earth, which means that we always see the same side of the Moon.

29. Distance to the Moon from Earth is 384,402 km (238,856 mi).  You could fit all the planets of our system in there, with room to spare.

30. Moon gravity is 1/6 of Earths.  If there was a pool on the Moon, swimmers could jump out of the water like dolphins, launching themselves more than a meter high.

31. There is no dark side of the Moon. The side that we don’t see is illuminated by the Sun as often as the side that we face.

32. Every year there are at least 2 lunar (Moon) eclipses, but it can happen that there are no solar eclipses. While the solar eclipses are rare, they still occur at least once every 18 months. The reason why we feel it’s much rarer than that is because they can be seen only from a fairly small area on the Earth.

33. Lunar eclipse happens when the Moon passes into the Earth’s umbra (shadow), which means that Earth is blocking the sunlight that usually falls on the Moon. This event can happen up to four times per year.

34. During the lunar eclipse, we still see the Moon, but it has a weak reddish tint. We sometimes call it the Blood Moon.

35. A Blue Moon is not really blue. It’s just a name for a second full moon that happens in one month, every now and then.

36. The solar eclipse occurs when the Moon passes right in front of the Sun, and it casts its shadow on Earth. The area of Earth that is in the Moon’s shadow is the only part on Earth where that particular eclipse can be seen. This is the only time when we can see the Sun’s corona from the Earth.

37. Mars is the fourth planet from the Sun, and it is the second smallest planet in our solar system. It has much weaker gravity than Earth:  with the gravity of 38%, a 100 kg person would weight only 38kg on Mars!

38. The red planet is also known for having some of the most impressive surface features. It is the home of Olympus Mons, the largest volcano in the solar system, and Valles Marineris a vast network of Canyons, second only to the rift valleys on Earth.

39. Olympus Mons is almost 22 km high, more than 2.5 times as tall as our highest mountain Mont Everest.

40. Mars has two tiny moons: Phobos and Deimos. It is believed that these moons are actually asteroids that have been caught up in the Mars’s asteroid field. The names of these satellites mean Fear and Dread, which is very suitable for the companions of the roman god of war.

41. The outer planets are Jupiter, Saturn, Uranus and Neptune. These humongous planets are also known as Jovian planets, in honor of Jupiter, the biggest of them. These planets together make up 99% of the mass that is orbiting the Sun.

42. Jupiter and Saturn are made of primarily hydrogen and helium, while the Uranus and Neptune have more icy components – a reason why these two are often called the ice giants.

43. Each of the outer planets has rings around it, but only the Saturn’s’ are visible to us from Earth. These rings are composed of small chunks of ice and rock, and they are surprisingly thin (less than a kilometer thick).  If Saturn’s rings were a meter long, they would be 10000 times thinner than a razorblade.

44. The Saturn has seven distinct rings. It is unknown why these rings are so prominent, but it is believed that it has something to do with the large number of moons that orbit Saturn. The rings have a radius of about 250000 km.  If one was to drive a car on one of the Saturn’s rings, at the speed of 100 km/h, it would take over 14 weeks to finish one lap.

45. The biggest moon that is orbiting Saturn is Titan. It is the only natural satellite that has dense atmosphere, mostly composed of nitrogen. Due to its low surface temperature of 94 K (−179.2 °C), it has lakes of methane, which makes it the only celestial body that we know of that has surface liquid, besides the Earth.

46. Jupiter is the biggest planet in our system, over 300 times bigger than Earth. It is so big that it is sometimes considered a failed star.  In fact, it emits more energy than it receives from the Sun.

47. Jupiter has a huge perpetual storm that rages in its upper layers, known as the Great Red Spot. It is so big that the whole Earth could fit into it. Gas giants have a very turbulent atmosphere, so storms such as this are fairly common. True enough, both Neptune and Saturn have their own spots, called the Great Dark Spot and the Great White Spot, respectively.

48. Jupiter has 67 natural satellites (or moons), the highest number of all the planets in the solar system. The largest and most famous are Io, Europa, Ganymede and Callisto.

49. Pluto is not the only dwarf planet in our system. Besides Pluto there are four other dwarf planets in our system: Ceres, Haumea, Makemake and Eris.

50. All the dwarf planets, except Ceres, are called the Plutoids in honor of the ex-planet Pluto. This designation is reserved for all the dwarf planets that orbit the Sun beyond Neptune.

51. The definition of a planet has been set at an astronomical conference in Prague, Czech Republic, in the summer of 2006. The new definition states that the planet:  Is in orbit around the Sun.  Has sufficient mass to assume a nearly round shape.  Has cleared the neighborhood around its orbit. (This means that there are no other celestial bodies of similar size in its orbit path.)

52. The main difference between a planet and a dwarf planet is that the dwarf planets have not cleared their neighborhood. Dwarf planets tend to orbit in zones shared with similar objects that can cross their path around the Sun, such as the asteroids. Dwarf planets are also smaller than the planet Mercury, the smallest planet.

53. There is an asteroid belt that orbits Sun between Mars and Jupiter. It is believed that these asteroids are remnants of a planet that failed to form during the solar system creation.  Asteroids can vary in size from a few meters to hundreds of kilometers.

54. Contrary to the movies and popular belief, the asteroid belt is fairly easy to maneuver in a spacecraft. Even though there are over a million asteroids estimated in the belt, they populate such a huge area of space that the distances between individual asteroids are at least several kilometers.

55. The crown of the asteroid belt is Ceres, recently classified a dwarf planet. Ceres has a radius of around 950km, and strong enough gravity that it pulled itself into a roughly spherical shape, granting it the almost-planet title.

56. The solar wind is a combination of particles, mostly ionized atoms from the stars corona, and magnetic fields produced by the star. It bathes our planet constantly, and the radiation would be deadly, if we were not protected by Earth’s magnetic field.

57. The area behind Neptune is called the Kuiper belt. It is a disc shaped region of comets, asteroids and dwarf planets, including Pluto. There are estimated thousands of bodies larger than 100 km and trillions of comets. Even the big bodies are not typical asteroids, but frozen liquids and gasses such as methane, ammonia and water.

58. Comets are space snowballs, composed of frozen water and gasses, rock and dust. The nucleus of a comet is usually not bigger than 10 km, but as the comet approaches the Sun and the frozen gases begin to evaporate, the nucleus can expand to over 80 000km.

59. The tail of a comet appears when it gets close enough to Sun and starts to melt. It is caused by the radiation pressure from the Sun which “blows” away some of the matter from the evaporating comet nucleus, which is why the tail always faces away from the Sun. These tails can be even millions of kilometers long.

60. The earliest recorded comet is the Halley comet, which was first observed in ancient china in 240 B. C. It makes one orbit around the Sun every 75 years.  Famous writer, Mark Twain, was born on the year when the Halley comet passed, and died on the year when it went by again. Both times he had missed it.

61. Exoplanets are the planets we found that are outside our solar system. These extrasolar planets are very hard to detect, and only in the past 10 years or so have we been able to regularly find new ones. We have so far discovered over 2000 exoplanets.

62. The smallest recorded exoplanet is twice the size of the Moon, while the most massive has almost 30 times the mass of Jupiter. This gas giant is so big that is uncertain whether it’s a planet, or a brown dwarf (the smallest type of a star).

Humans in space

63. The first man on the Moon was Neil Armstrong who flew with Buzz Aldrin, and Michael Collins on the Apollo 11 rocket.  However, he is not the only one who had that honor:  There were twelve people in total that have so far walked on the Moon, in 6 different Apollo missions. These astronauts spent a total of 90 hours on the Moon, in 14 Moonwalks.

64. The last man on the Moon was Eugene Cernan, with the NASA’s Apollo 17 mission. Before he left the Moon surface, he scratched the initials of his daughter’s name in one of the lunar rocks. Since there is no atmosphere on the Moon, these initials, along with the footsteps of all the astronauts and rover tire tracks, are still there.

65. There are six American flags planted on the Moon (one by each mission that landed), but they are all bleached out and completely white now, due to radiation.

66. The famous speech made by the American president Nixon for the first Moon landing had a much darker version.  There was a special, alternative, speech written in case that the Moon mission was a failure and that the astronauts weren’t able to safely return home.

67. Space is a vacuum, which means that there is almost no pressure, and no matter density. However it is not a perfect vacuum, since it is not completely empty. We haven’t been able to produce that level of vacuum in our Earth laboratories yet.

68. There is no sound in space. The reason is that the sound waves are actually mechanical waves produced by oscillating atoms and molecules. Since there is neither in sufficient quantity in space, there are no sound waves.

69. Only three people have died in space. Russian astronauts Georgy Dobrovolsky, Vladislav Volkov, and Viktor Patsayev, the crew of Soyuz 11, suffered a malfunction while returning to Earth, at the distance of 168 km. Their bodies have been successfully recovered, and they were given a hero’s funeral. Unfortunately, there are many more astronauts that died in Earth’s atmosphere during the launch or re-entry of their spacecraft. Crews of space shuttles Challenger and Columbia have been tragically lost, and many astronauts and cosmonauts have perished during various training exercises or test launches, over the years.

70. Amazingly, humans can survive in space unprotected, for a short time.  A human without a space suit can survive the rigors of vacuum for around 30 seconds to a minute conscious, and several more minutes blacked out, if the rescue came in time.

71. One of the first things that happen with humans and animals exposed to hard vacuum is that their blood begins to boil. Even though space is super cold, the lack of pressure means that the boiling point of all liquids is much lower. Second, the air in the lungs would expand rapidly, destroying the lungs, which means that a person trying to survive must exhale all the air it has in its lungs, prior to being exposed to vacuum, unless they want to suffer explosive decompression.

72. Temperature of space is balmy 3K, or -270 C. That is only three degrees above absolute zero, the lowest possible temperature.

73. There have been 536 people in space so far. They have spent a total of over 29 000 days, with the record for the longest time in space belonging to the Russian astronaut Valeri Polyakov, who spent 437 days in space, living on a space station MIR. Recently, astronauts Scott Kelly and Mikhail Korniyenko both spent 340 days aboard the International Space Station, before returning together to Earth.

74. We have built 9 manned space stations so far, including the US Skylab, Salyut and Almaz stations.

75. There were three modular space stations built, of which 2 are still functional. The first one, the Russian Mir station was operational for 25 years, before it was abandoned, and subsequently made a controlled burn out in the atmosphere.

76. Mir station actually had a slight infestation problem prior to its dismantling. Not in a real sense, mind you, but there were over 140 different kinds of microbes found on it, some of which were responsible for the corrosion on the station.

77. Currently operational stations are the International Space Station, and the Chinese Tiangong station. These stations can’t house astronauts indefinitely because they don’t have good radiation protection, and can’t recycle or create food and water fast enough.

78. The ISS has 13 modules, with 3 new modules scheduled for installation. It is made by combined effort of the American, Russian, European, Japanese and Canadian space agencies. The whole project cost over 150 billion dollars so far.

79. The ISS orbits Earth every 90 minutes, which means that the crew of the station sees 16 sunsets and sunrises daily!

80. There have been almost 200 space walks made by the ISS astronauts so far. 222 astronauts from 18 countries have visited the International Space Station.

81. The people on both stations experience microgravity. While it seems like it’s a zero-g environment, it’s a bit more complicated:  The reason why there is no gravity on space station is not because it is out of Earth’s gravity field, but rather because it is in constant state of free-fall.

82. Because of the lack of gravity on the stations, astronauts can grow in height up to 2 inches during their stay on the station. Unfortunately, lack of gravity also negatively influences their bone density, because there is no weight they carry constantly. In order to combat this, all astronauts have a very rigid daily workout regimen on specially designed equipment.

83. The length of the ISS is 357 feet, almost the length of an American football field.  It weighs almost a million pounds, and has over an acre of solar panels that powering it. The internal pressurized volume is equivalent to that of a Boeing 747.

84. If you were to spill the water, or any other liquid in space, it would form up in a sphere and float, due to the liquid surface tension.  This also happens to human tears, so it’s not easy to cry in space.

85. The current space suits are a thing of wonder: They have a special middle layer that blows up, in order to pressurize the astronaut’s body. The visor has air circulation so that it doesn’t get misty due to the water evaporation.

86. The furthest man-made objects currently are two voyager probes. Voyager 1 has officially left the solar system on August 25, 2012, 35 years after its launch.

87. Both voyagers carry a golden record. This record contains the sounds from Earth, selected by a special committee, and on its cover are etched symbolic directions to our home planet. The Pale Blue Dot is a famous photo with a commentary by Carl Sagan, which is also made by Voyager 1.

88. There are three NASA rovers on mars – Spirit, Opportunity and Curiosity. We lost the contact with the Spirit after more than 6 years of operation which is 25 times the planned mission duration. The other two rovers are still operational.

89. Curiosity is the biggest and newest Mars rover. It is the size of a car and has been on Mars since August 6, 2012 which is 1298 sols (Mars days), or 1333 Earth days.

90. There are special playlists of songs that are played by mission control every day, depending on the activities planned for the rovers. The lonely Curiosity was programmed to sing happy birthday to itself.

91. We have managed to land a probe on a comet! The Philae Lander, of the Rosetta mission was the first ever man-made object to make a soft landing on a celestial body that’s not a planet or a moon. (NEAR shoemaker probe made an improvised landing on an asteroid before, but that wasn’t a planned part of a mission.)

92. There have been over 30 monkeys and 12 dogs in space so far. The most famous dog is Laika, a Russian mutt who was the first dog to reach the space. Unfortunately Laika didn’t survive the trip, and the first dogs that were successfully recovered after their space trip were dogs Belka and Strelka. The record for longest space flight by dogs was achieved by space dogs Veterok and Ugolyok on March 16, 1966, when they landed after 22 days in space.

93. Besides dogs and monkeys, we have launched cats, guinea pigs, rabbits, spiders, mice, fruit flies, moths and a whole host of other small animals into space.

94. Tardigrades are the most resilient organisms known to man. These micro-animals, only half a millimeter large can survive unprotected in space for 10 days.

95. All our satellites, probes and rockets leave a lot of garbage behind. In fact, there is a debris field surrounding Earth with more than 500 000 pieces larger than one centimeter. These pieces are routinely tracked by stations on Earth, in order to control potential damage to our satellites and stations.

96. New horizons is the first probe we sent to investigate Pluto and some of the Kuiper belt objects. It also carries a number of Earth mementos on it, among which are the ashes of Clyde Tombaugh, the man who discovered Pluto in 1930.

97. Charon is the largest of five Pluto’s moons. Charon is so big that Pluto and Charon actually orbit around one another, like binary stars do. Unlike Pluto, whose surface consists primarily of frozen nitrogen and methane, there is evidence of frozen water on Charon, along with active cryo-volcanoes.

Facts about stars

98. Stars are classified by their color, size and temperature. Our Sun is a GV2 type yellow dwarf, and it is a main sequence star. (These main sequence stars are the most common.)

99. Stars are born in nebulae. A nebula is a huge interstellar cloud of gas that consist primarily of hydrogen and helium, and, to lesser extent, dust and other ionized gasses.

100. Stars exist in the state that is called plasma, and it is actually the fourth fundamental state of matter.  This is actually the most abundant form of ordinary matter (yes, there is unordinary matter) in the universe, even though we don’t witness it on Earth at all, except in the labs. (Well, and if you cut a grape in half and microwave it. – do not do this at home!)

101. A protostar is a star infant of a sort. This is the name used for a star that is still gathering mass from its parent molecular cloud (Nebula). This is the first stage of the star evolution, and it lasts for about a billion years for stars that are similar in size to our own Sun.

102. Although we see stars as specks of light in the sky, sometimes that speck is not just one star. Binary star systems have two stars instead of one that orbit around each other. The craziest part is that the orbiting objects don’t have to be stars. They can be black holes, neutron stars, white dwarfs, or any other celestial body.

103. Besides binary, there are also other multiple star systems. The most common of these are trinary systems, where three stars orbit around each other.

104. The most complex multiple systems we have discovered are septuple star systems, which means there are 7 star orbiting around each other in a ludicrously complex orbit. To top it off, we found 2 such systems already.

105. Nuclear fusion is a chemical reaction in which two atoms fuse into one. This is the process that is responsible for the huge quantities of energy produced in stars. Stars begin as huge balls of the two lightest elements, Hydrogen and helium, and slowly fuse those into heavier and heavier elements.

106. All the chemical elements up to Iron (28th element) are produced by nuclear fusion in the stars. The Iron is the limit because fusing heavier elements requires more energy than would be produced by the reaction.

107. Since the human beings, animals and plants are mostly made of carbon, oxygen, hydrogen and other fairly light elements mostly produced in stars, there is a tiny bit of a star in each and every one of us. In a way we are all made off star stuff, as Karl Sagan said.

108. Star’s lifespan depends on the amount of fuel it has. Surprisingly, the bigger the star, the shorter it’s life is. This is due to the fact that massive stars produce tremendous amounts of energy, and burn through their fuel reserves quickly.

109. Our Sun has an estimated lifespan of around 10 billion years, and we’re half way through it. When it depletes its reserves it will first become a red giant, before dying out.

110. When stars die (their reserve of fusionable elements is depleted), depending on their size several things can happen:  They become white dwarfs and slowly die out, or they go out in the blaze of glory in a majestic explosion that is called a supernova.

111. Supernovae (plural of supernova) are some of the most energetic events in cosmology. They can briefly outshine whole galaxies.

112. The tiniest stars, red dwarfs, might live up to an amazing 10 trillion years, which is almost 800 times the current age of the universe. These stars are also the most numerous.

113. The white dwarfs are the remnants of dead stars. These tiny Earth-sized balls are composed of electrons and can shine for millions of years. The heat and energy they emit is only due to their stored thermal energy (i.e. heat), since no nuclear fusion or any other chemical process is present.

114. Our Sun is to become a white dwarf at the end of its life, after it goes through a red giant phase. When the Sun becomes a red giant, its outer layers will engulf Earth. That won’t be pleasant, I assume.

115. The Sun has the size of around million Earths.

116. Sun burns up over four million tons of matter each second in its core. This matter is converted into energy and released in the form of neutrinos and solar radiation.  The Sun has converted over 100 times the mass of Earth into energy so far.

117. The Sun increases its energy production over time, due to heavier elements being used for nuclear fusion. It is estimated that it is 30% brighter now than when it started its main-sequence life.

118. The oldest recorded star is conveniently nicknamed Methuselah. This elderly statesman is estimated to be as old as the universe itself.  

119. Star colors depend on the temperature of the star. Contrary to what is logical to us, blue is hot and red is cold. This is because the hotter stars emit light on the shorter, more energetic wavelengths, which we see as blue, while the red color is on the opposite side of the color spectrum with longer wavelengths.

120. There are no green stars. Stars that are neither really hot nor cold emit white light that we can see as green when we use certain filters.

121. Neutron stars are the smallest and densest stars that we know of. They are made entirely of neutrons, subatomic particles with no charge, instead of atoms. They are incredibly hot with temperatures of over 600000 Kelvin.

122. Neutron stars can have a radius of about 10 kilometers, but can pack 2 Sun masses in their (comparatively) tiny volume.  A teaspoon of neutron matter from the core would weigh around 10 billion tons, which is similar to the weight of an average Earth mountain.

123. The star nearest to Earth, besides Sun, is Proxima Centauri, 4.2 light years away. To try and understand this distance, here’s a little example:  The space shuttle can reach speeds of 30000 kilometers per hour. If you were to take the shuttle, it would take you around 150000 years to reach our closest neighbor.

124. The black hole is an object so massive and dense that its gravity pull is too strong for even light to escape.

125. Black Holes can be both small and large.  Smallest black holes can be the size of an atom, but hold a mass of a large mountain, while the biggest can be larger than Earth.

126. Supermassive black holes are the largest black holes we know of, and they can have a mass of millions of Suns. In the center of each galaxy is a supermassive black hole, around which the whole galaxy rotates.

127. The Sagittarius A is our galaxy’s very own supermassive blackhole.  It is a large ball with the mass of 4 million Suns and it could fit several Suns, or a few million Earths, in it.  

128. The twinkling of the stars is called scintillation. Stars are so far away, that they are actually just points of light, which means that when they reach the Earth, due to the changes of direction (known as refraction), caused by the atmosphere, their light doesn’t reach any single point, including our eyes and telescopes, continuously.

129. Any non-twinkling lights in our sky are either planets from our system, or artificial satellites orbiting Earth. This is because these objects have actual dimensions, so some light always falls on the same place. Really, we can see planets as little discs of light with a sufficiently powerful telescope.

130. Even planets can scintillate though, if we are looking at them when they are low in the sky, near the horizon. This is because the atmosphere is densest in that direction, and there is more of it, so refraction is much higher.

131. Both stars and planets shine steadily, when they are seen from the international space station.

132. Stars do not have uniform composition. Like Earth, and other planets, they have several layers, which have different density, temperature and composition.

133. The surface of a star is called the photosphere. Above it starts the stellar atmosphere- which in turns consists of a Chromosphere and a Corona. Yep, that’s a lot of layers.

134. Photosphere is the layer which we actually see. After it reaches the star’s surface, the energy produced in the star’s interior is finally free to leave and travel through the vacuum of space.

135. Corona is the furthest layer of the Sun, and at the same time the hottest. This effect of inverse temperature has been confusing scientists for decades, and it’s still not fully understood. The corona can only be seen from the Earth during the total eclipse.

136. Heliosphere is the vast magnetic bubble produced by the Sun, which contains our complete solar system, way beyond the orbit of Pluto.

137. Solar flares are sudden and huge flashes that occur on Sun’s surface, but jump out throughout all of the outer layers, usually accompanied by a spectacular coronal mass ejection. Solar flares usually appear in the areas near the active sunspots, due to the intense magnetic fields that appear there.

138. If there are so many stars in the universe, why isn’t our night sky completely white with the light from all of them? This question is known as the Olber’s paradox.

139. The answer to the Olber’s paradox is twofold:  First, some stars give away light too weak to be seen by naked eye.  Second, and more important, light from many stars hasn’t reached us yet. The speed of light is finite, and the universe is bigger than it is old. (Yeah, that sentence makes sense only in cosmology.)

140. All the stars we see in our night sky are classified into distinct magnitudes. The reason why we perceive stars’ brightness as distinct categories is due to the nature of how brain interprets information we receive with our eyes.

141. This method of star classification was developed in the ancient Greece. Our eyes can see 6 magnitudes, one being the brightest and 6 the faintest. Each magnitude is two times brighter than the next one.

The weird stuff in outer space

142. Quasars are the most energetic sources, and the most luminous objects in the universe. They can be 100 times brighter than a whole galaxy. Their name is an abbreviation of the term “Quasi-Stellar Radio Sources”.

143. Solar flares can be very dangerous, as they produce streams of charged particles that can damage our satellites, and pose risks to astronauts’ health. This radiation hazard is one of the biggest concerns for all manned missions that might be planned in the future.

144. The great attractor is a mysterious gravitational anomaly we discovered 250 million light years away. While we are uncertain what it is, we assume that it is probably a large collection of galaxies, or a galactic supercluster, that pulls towards it everything in its neighborhood.

145. Neutrinos are a special sort of elementary particle. These particles are electrically neutral and have virtually no mass. Because they don’t interact with normal matter, they can go through planets and whole stars without slowing down at all. It is incredibly difficult to detect them, and we use huge pools of water infused with cadmium chloride to spot them.

146. Higgs Boson is a theoretical particle that has no spin, no electric charge, but has mass. It is kind of the opposite of the neutrino. While we still can’t claim that we detected the Higgs Boson, scientists are pretty certain that they managed to detect one in the Large Hadron Collider in 2013.

147. There are four fundamental forces in the universe: gravitational, electromagnetic, strong nuclear, and weak nuclear.

148. Time dilation is an effect that appears when something is traveling near the speed of light. If an astronaut was to launch from Earth and travel at a near-speed of light to our closest neighbor, Proxima Centauri it would take him 4.5 years. However, while years would pass on Earth, the astronaut would feel like he spent months, maybe even days on his journey.

149. The oh-my-god particle is the fastest particle we ever recorded. It’s a proton, one of the two particles that make atomic nucleus, which was moving at 99.99999999999999999999951% speed of light. This single particle with a mass of an electron has the equivalent kinetic energy of a baseball traveling at nearly 100 km/h.  If this particle was to travel 100 000 light years across the Milky Way, that trip would last only 10 second from its point of view, due to the time dilation.

150. Besides the ordinary matter we are all familiar with, there are all kinds of matter that is either theoretical or recently discovered. We now separate matter into baryonic and non baryonic madder, and light and dark matter. Baryonic matter is made of standard atoms and molecules, and subatomic particles like protons, neutrons and electrons.

As you can see, universe is full of surprises, and we, as a human race, had our own share of adventures and crazy anecdotes to add to it!