There are are somewhere between 1022 and 1024 -stars in the universe.
All the stars we can see with the naked eye are in the Milky Way Galaxy.
About 3,000 stars are visable from one place on earth with the naked eye. The andromeda galaxy [2.3 million light years away] can be seen with the naked eye A few galaxies (andromeda is the bigest) appear as fuzzy little blobs to the naked eye in ideal conditions (low light and clear skies).
If you had perfect eyesight and traveled to completely dark skies in both the Northern and Southern Hemispheres, and there was no Moon, you might be able to get to count up almost 9,000 stars.
With a good pair of binoculars, that number jumps to about 200,000, since you can observe stars down to magnitude 9. A small telescope, capable of resolving magnitude 13 stars will let you count up to 15 million stars.
How many stars are there in the universe? - Sky & Telescope |
Stars vary considerably in size:
- Supergiants are the largest stars, and may have diameters several hundred times the size of the Sun.
- Giants are more common than Supergiants, and have diameters 10 to 100 times as large as the Sun.
- Red Giants have cooler temperatures than giants, and are thus less bright, but their size is still massive.
- Medium-size or dwarf stars are about as large as the sun. About about 800,000 miles in diameter
- White dwarfs are small stars (smaller than the distance across Asia).
Nebula - an interstellar cloud of dust, hydrogen, helium and other ionized gases. Most nebulae are large, reaching sizes of even hundreds of light years in diameter.
Galaxies vary in size just a few tens of millions of stars to a mass of 2 quadrillion (2 x 1015) Suns.
The Universe probably contains more than 10 Trillion (1013) galaxies.
The Milky Way galaxy contains about 300-500 billion (5x1011) stars.
Our Solar System is in the Orion Arm of the Milky Way galaxy about 26,000 light years from the center.
Clusters of Galaxies - Galaxies are not uniformly distributed. They are grouped in clusters of up to 50 galaxies which in turn are part of larger groups.
We are part of the following hirearchy:
Laniakea Supercluster Complex
Local group: Andromeda, Milky Way and 50+ dwarf galaxies.
Superclusters - The Milky Way is part of the virgo supercluster.
Super Cluster Complexes: - large structures of galaxies, called "filaments", "walls" or "sheets", that may span between several hundred million light-years to one billion light-years.
The Laniakea Supercluster is the supercluster that contains the Virgo Cluster, Local Group, and by extension our galaxy, the Milky Way.
Filaments, thread-like structures, are the largest known structures in the universe, that form the boundaries between large voids in the universe.
Supercluster - Wikipedia
The Universe within 100 million Light Years - The Virgo Supercluster
Universe - The diameter of the observable universe a sphere around 92 billion light-years.
The cosmos is 13.7 billion years old but the stretching of space with its expansion after the Big Bang means that simple distance measurements do not apply.
See How Big is the Universe? | space.com
The Flatness Problem :
Our universe is apparently flat. That is, it appears to have just the "right" density--or nearly so--to continue its slow expansion forever. Too much matter, and the universe eventually collapses in on itself under the influence of its own gravitational pull. Called the "Big Crunch". Too little matter, and gravity will never be able to halt the expansion of the universe. The universe eventually be populated only by gas, dust and the relics of stars, growing increasingly cold with its infinite expansion. This bleak scenario is called the Big Chill.
See The Flatness Problem at NCSA - U. Ill.
Expansion Speeds up:
It was assumed that the gravitational force of dark matter would slow down the expansion of the universe. However, a 1998 discovery showed that expansion is speeding up. This has been attributed to "Dark Energy" which is not well understood.
It is speculated that this shift from slowing expansion to accelerated expansion occurred about 5 billion years ago. See The Expanding Universe: From Slowdown to Speed Up: Scientific American.
Current estimates are that Dark Energy makes up 73% of the universe, Dark Matter makes up 23% of the universe. The visible matter that we are familiar with, only makes up 4% of the universe.
See: A Quintessential Introduction to Dark Energy from Paul Steinhardt at Princeton.
A 2008 study using Wilkinson Microwave Anisotropy Probe (WMAP) data found that distant galaxy clusters appear to be zooming through space at phenomenal speeds that surpass 1 million mph. The clusters were tracked to 2.5 billion light-years away - twice as far as earlier measurements, along a path roughly centered on the southern constellations Centaurus and Hydra .
Dark flow is the name given to this.
The dark flow is controversial because the distribution of matter in the observed universe cannot account for it. Its existence suggests that some structure beyond the visible universe -- outside our "horizon" -- is pulling on matter in our vicinity.
At a 2002 NASA press release the Hubble team announced they had computed the age of white dwarfs in globular cluster M4 in the Milky Way to be 12-13 billion years old. These extremely old, dim stars provide a completely independent reading of the universe's age without relying on measurements of the universe's expansion, which came up with estimates of 14 Billion years. Because the first stars formed less than 1 billion years after the universe's birth in the big bang these findings are consistent.
Astronomers say that in around 100 trillion years (1014) all stars will decay into white dwarfs or explode in supernovas leaving behind a neutron star or black hole. So the universe will be very dim. Most of the radiation a neutron star is X-rays with little in the visible spectrum.
The white dwarfs will eventually decay into brown dwarfs (originally called black dwarfs) which are too low in mass to sustain hydrogen fusion.
There are at least one hundred billion (1011) galaxies in our Universe.
There are 70 sextillion (7x1022)stars in the visible universe
Mostly H with some He
-> Hyper Novi
1 Billion Yrs
Stars (Initially H fused to create He)
As a star starts to use up He it starts to shrink and gets hotter
so it can burn He.
3 He -> C
Creates more elements up to Fe (Iron)
Creats super Nova which creates heavier elements
See: Timeline of the Big Bang - Wikipedia, the free encyclopedia
4.5 Billion - Our Sun
Terms - Glossary:
CMB - Cosmic microwave background
ESA - European Space Agency
GUT - Grand unification Theory
Hypernova - Supernova of a hypergiant star.
Nebula - Interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases.
Quasar - A compact region in the center of a massive galaxy surrounding
its central supermassive black hole. They are sources of electromagnetic energy,
including radio waves and visible light, that were point-like, similar to stars.
Supernova - A stellar explosion of a dying massive star.
ULASJ1234+0907 - 10,000 times the mass of the super-massive black hole in our own Milky Way
WMAP - Wilkinson Microwave Anisotropy Probe
Cosmology: A Short Bibilography. at NCSA U. Ill Urbana-Champaign
Our Cosmic Habitat, Martin Rees
(1) Until the mid-1990s the data on the rate cosmic expansion were so uncertain
that the best estimates of the age the universe stood at between 10 and 20 billion years. New calculations have zeroed in on 13.7 B years.
In 2004 Astronomers announced that "The Universe is is at least 156 Billion light years across."
The cosmos is 13.7 Billion years old but the stretching of space with its expansion after the Big Bang means that simple distance measurements do not apply.
Astronomers realise the Universe is more complex. It has been expanding ever since the Big Bang when energy, space and time itself began.
To get the picture try to imagine the Universe a million years after the Big Bang. Light travels for a year, covering one light-year. But at that time, the Universe was about a thousand times smaller than it is today meaning that one light-year has now become stretched to about a thousand light-years.
See The Size of the Universe: A Hard Question
History > Universe
and Universe timeline here.
Books - Guides:
The Astronomical Companion by Guy Ottewell
Big Bang Theory - Crystalinks
The Physics of the Universe - Timeline of the Big Bang
The Description, Origin, and Development of the Universe at nasa.gov
Foundations of Big Bang Cosmology at nasa.gov
Cosmic Evolution: An Interdisciplinar Approach at Tufts.
TimeLine at HistoryOfTheUniverse.com
Frequently Asked Questions in Cosmology at UCLA
Celestial Coordinate System
Free star charts
Your Sky Object Catalogue: Named Stars
Hubble Space Telescope Images
European Space Agency (ESA)
last updated 17 Jan 2015