[/caption]
Here’s a question: how big is Earth? Let’s take a look at how big our planet is.
First, the equatorial diameter of Earth is 12,756 km. In other words, if you dug a tunnel on the equator that went straight down and went right through the center of the Earth, it would be about 12,756 km long. Just for comparison, that’s about 1.9 times the diameter of Mars. And only .09% the diameter of Jupiter.
The volume of Earth is 1.08 x 1012 km3. Written another way, that’s 1.08 trillion cubic kilometers of rock and metal. Again, it’s about 6.6 times more volume than Mars.
The surface area of Earth is 510,072,000 square kilometers. Of that, 29.2% is covered by land and 70.8% is covered by water. Just for comparison, that’s 3.5 times as much surface area as Mars.
The mass of Earth is 5.97 x 1024 kg. Here that is written out: 5,970,000,000,000,000,000,000,000 kg. Yeah, that’s a really big number. And yet, it’s only 0.3% the mass of Jupiter (and Jupiter is mostly lightweight hydrogen).
Cumulonimbus clouds are a type of cumulus cloud associated with thunder storms and heavy precipitation. They are also a variation of nimbus or precipitation bearing clouds. They are formed beneath 20,000 ft. and are relatively close to the ground. This is why they have so much moisture. Cumulonimbus clouds are also known as thunderheads due to their unique mushroom shape.
These clouds often produce lightning in their heart. This is caused by ionized droplets in the clouds rubbing against each other. The static charge built up create lightning. Cumulonimbus clouds need warm and humid conditions to form. This gives them the moist warm updrafts needed to produce them. In some instances a Thunderhead with enough energy can develop into a supercell which can produce strong winds, flash floods, and a lot of lightning. Some can even become tornadoes given the right conditions.
Despite the heavy rainfall these clouds produce, the precipitation normally just lasts for around 20 minutes. This is because the clouds require not only a lot of energy to form but also expend a lot energy. However, there are exceptions to the rule. There are also dry thunderstorms which are cumulonimbus clouds whose precipitation does not touch the ground. This type is common in the Western United States where the land is more arid. It is often cited as a cause of wild fires.
An overlooked result of Cumulonimbus clouds are flash floods. This was proven recently in Atlanta, Georgia area of the United States. The state had gone through a two year drought and water supplies such as creeks and rivers were low. However the fall season brought with it the end of the drought and a lot of Thunderstorms. Even though Atlanta is not near any major waterways, the resulting flash floods were on a scale seen only with areas near major rivers with wide flood plains. This demonstrates how much precipitation that Cumulonimbus clouds can produce even in a short amount of time.
Cumulonimbus clouds are a perfect example of how difference in altitude can affect the formation of clouds. Cumulonimbus clouds form in the lower part of the troposphere, the layer of the atmosphere closest to the surface of the Earth. This region due to evaporation and the greenhouse effect produces alot of the warm updrafts that make creation of cumulus and cumulonimbus clouds possible. The turbulence created by the friction between air and the surface of the Earth combined with stored heat from the sun helps to drive the majority of weather.
If you enjoyed this article there are others on Universe Today that you will be sure to enjoy. There is a great article on cloud types and another on the composition of the Earth’s atmosphere.
Galileo Galilei's telescope with his handwritten note specifying the magnifying power of the lens, at an exhibition at The Franklin Institute in Philadelphia. Credit: AP Photo/Matt Rourke
The history of the telescope dates back to the early 1600s. Galileo Galilei is commonly credited for inventing the telescope, but this is not accurate. Galileo was the first to use a telescope for the purpose of astronomy in 1609 (400 years ago in 2009, which is currently being celebrated as the International Year of Astronomy). Hans Lipperhey, a German spectacle maker, is generally credited as the inventor of the telescope, as his patent application is dated the earliest, on the 25th of September 1608.
Lipperhey combined curved lenses to magnify objects by up to 3 times, and eventually crafted sets of binocular telescopes for the Government of the Netherlands.
There exists some confusion as to who actually came up with the idea first. Lipperhey’s patent application is the earliest on record, so this is usually used to settle the debate, although another spectacle-maker, Jacob Metius of Alkmaar, a city in the northern part of the Netherlands, filed for a patent for the same device a few weeks after Lipperhey. Another spectacle-maker, Sacharias Janssen, also claimed to have invented the telescope decades after the initial claims by Lipperhey and Metius.
Regardless of the inventor, most of the earliest versions of the telescope used a curved lens made of polished glass at the end of a tube to magnify objects to a factor of 3x. To learn more about how a telescope lens works, read our article on the telescope lens in the Guide to Space.
Galileo heard news of the telescope, and constructed his own version of it without ever seeing one. Instead of the initial 3 power magnification, he crafted a series of lenses that in combination allowed him to magnify things by 8, 20 and eventually 30 times. You can obtain a version of Galileo’s original telescope today, at the Galileoscope web site.
The lens telescope is still in use today in smaller telescopes, but many larger and more powerful telescopes use a reflective mirror and eyepiece combination that was initially invented by Isaac Newton. Called a “Newtonian” telescope after its inventor, these types of telescopes have a polished mirror at the end of a tube, which reflects the image into an eyepiece at the top of the tube. More information about Newtonian telescopes can be found in our Guide to Space article here.
Here’s a few more links on the history of the telescope:
The Hubble Space Telescope distribution of dark matter - indirect observations (HST)
WIMPs are Weakly Interacting Massive Particles, hypothetical particles which may be the main (or only) component of Dark Matter, a form of matter which emits and absorbs no light and which comprises approx 75% of all mass in the observable universe.
The ‘weakly’ is a bit of a pun; WIMPs would interact with themselves and with other forms of mass only through the weak force (and gravity); get it? More plays on words: WIMP, the word, was created after the term MACHO (Massive Astrophysical Compact Halo Object) entered the scientific literature.
WIMPs are massive particles because they are not light; they would have masses considerably greater than the mass of the proton (for example). Being massive, WIMPs would likely be cold; in astrophysics ‘cold’ doesn’t mean ‘below zero’, it means the average speed of the particles is well below c. Neutrinos are weakly interacting particles, but they are not massive, so they cannot be WIMPs (besides, neutrinos aren’t hypothetical, and they’re hot, very hot … they travel at speeds just a teensy bit below c).
Or maybe they are … if there is a kind of neutrino which is really, really massive (a TeV say) then it would certainly be a WIMP! However, the latest results from WMAP seem to rule out this kind of WIMP-as-neutrino.
Looking for a picture of Earth from Space? Here is a collection.
[/caption]
Here’s a spectacular image of the earth with the full coverage of the Pacific Ocean. This image was obtained by the Galileo spacecraft on December 12, 1990 while on its way to planet Jupiter 1.6 million miles from the Earth.
The Blue Marble from Apollo 17
This is a spectacular full view of our planet earth. It was taken by the Apollo 17 during their journey to the moon in December 7, 1972. The south polar ice cap of Antarctica can be clearly seen in the image. This region constitutes 70% of the world’s freshwater. This photo of the earth was the first to feature the south polar ice cap.
A Stormy Atlantic
Here’s an image of different storms and hurricanes forming at the Atlantic Ocean. This image was generated using the data provided by the Geostationary Operational Environmental Satellite (GOES) satellite on September 3, 2008.
Earth - Western Hemisphere
Here’s a nice view of the earth particularly focusing on the Western Hemisphere. Earth is the third planet from the sun and is the only place in the universe where life is known to exist.
The Earth-Moon System
This is a nice view of the planet earth and the moon in one frame as seen from the Galileo spacecraft 6.2 million kilometers away.
Picture of Earth from Space
Here’s a picture of Earth from Space as well as the Moon. These images were taken separately and then stitched together on computer to show them together.
Earth from Space
This picture was taken by the Space Shuttle, and shows the Earth from high orbit. You can see how the clouds rise up into the atmosphere.
Earth from space
Here’s another picture of Earth. Again, this was taken from the space shuttle.
NASA satellite map of the Earth
This is a satellite map that shows all of the Earth.
This is the classic “Blue Marble” photo of Earth.
Earth from Space at Night
Earth from Space at Night
Here’s a photo of the entire Earth, seen from space at night. You can easily see cities and towns in North America, Asia and Europe. And you can also see vast regions of the Earth which are totally dark.
Chicago at night
Here’s a photo of the city of Chicago at night. It might look upside down, but that’s because it was captured from the International Space Station as it was passing over the city.
Tokyo at night
This night space image shows the city of Tokyo at night. The blue green glow in the photograph comes from the mercury vapor lighting that lines the streets of the city.
London at night
This space pic from night shows the city of London. You can see the brightest areas are the most densely populated, and the less dense areas are dimmer. You can see the ring road that surrounds London, as well as the path of the Thames river.
Los Angeles at night
Here’s one of the brightest cities in the world. It’s Los Angeles from space, seen at night.
A Crescent Earth at Midnight
Here’s an amazing picture of the earth in crescent. This breathtaking view of our planet was obtained by the Geostationary Operational Environmental Satellite (GOES-8) on June 22, 1996. GOES is primarily assigned in monitoring the weather particularly the development of storms and hurricanes in different parts of the earth.
Earth at Twilight
This is an amazing still photo of the earth taken during its transition from day to night. This beautiful photo was taken from the International Space Station in June 2001.
All Is Illuminated
This spectacular image of the crescent earth was captured by the Optical Spectroscopic and Infrared Remote Imaging System (OSIRIS) camera on board the Rosetta spacecraft in November 2007.
Houston, Texas at Night
Here’s a nice view of Houston, Texas at night as seen from the International Space Station on February 28, 2010. This photo was taken by the crew member of the Expedition 22 mission. Houston, Texas is the world’s energy capital.
Earth from Orbit
Manicouagan Reservoir. Credit: NASA
Here’s an image of the Manicougan Reservoir situated at Canadian Shield in the province of Quebec. This was taken from the International Space Station in December 1983. Manicougan Reservoir covers an area of about 1,942 km².
Sunset
This image of the sunset on earth was captured from the International Space Station by an Expedition 13 astronaut in August 10, 2006. Expedition 13 mission was able to accomplish a total of 2,886 orbits.
Expedition 11 Earth Observation Photos
This photo shows the Central Gulf Coast obtained from the International Space Station by an Expedition 11 astronaut in September 10, 2005.
Into the Eye of the Storm
This is a photo of the eye of Hurricane Alberto taken in August 19, 2000 during the Terra orbit 3571. Hurricane Alberto is a Category 3 hurricane in the Atlantic that lasted for 19.75 days.
Hurricane Emily and the Moon
This beautiful view of the eye of Hurricane Emily and the moon was captured from the International Space Station in July 16, 2005. Hurricane Emily is a Category 5 hurricane having a maximum wind speed of 160 mph.
Earth from the Space Shuttle
Sunrise in Space
This photo of the earth’s atmosphere during sunrise was taken in July 2005 by a Discovery crew member during the STS-114 mission. STS-114 mission was the first Return to Flight mission after the unfortunate loss of the Columbia space shuttle.
Onboard View - Space Shuttle Endeavour
This image of the earth was taken from the space shuttle Endeavor during the STS-59 mission in April 12, 1994. The image particularly shows the shuttle’s payload bay and the region of the Andes Mountains in Bolivia.
Sinai Peninsula and the Mediterranean Sea
Here’s a stunning image of the Sinai Peninsula and the Mediterranean Sea as seen from the space shuttle Atlantis. A crew member of the STS-125 mission took this photo during the mission’s first flight in space.
View of the Journey Home
Here’s a unique photo of the earth’s atmosphere taken by the crew members of Atlantis’ STS-125 mission during its preparation for landing on May 20, 2009.
STS-39 view of the Aurora Australis
Here’s a great view of the Aurora Australis taken in May 1991 by the STS-39 crew member onboard the space shuttle.
The Arctic Circle is a region on Earth that is marked as one of the five major circles of latitude on maps of our planet. It is located between the Arctic to its north and the Northern Temperate Zone to its south. Its counterpart in the Southern Hemisphere is known as the Antarctic Circle. In addition to the Antarctic Circle, the other three major latitude lines are the Tropic of Cancer, the Tropic of Capricorn, and the Equator.
The Arctic Circle is the farthest southern region that experiences polar day and polar night. A polar day is where it is 24 hours of continuous daylight, and a polar night is 24 continuous hours of darkness. North of the Arctic Circle more than one polar day and night occur per year. However, the Arctic Circle only experiences a polar day and night once a year on the June and December solstices respectively. Usually, those days fall on the 21st of each month. Polar day is also known as midnight sun and polar-summer while polar night is also known as darkness at noon or midwinter darkness. The Antarctic Circle also experiences a polar day and a polar night once a year.
Due to the Earth’s shifting axial tilt – a fluctuation of 2° during 40,000 years – which is especially a result of the Moon’s orbit, the Arctic Circle is moving. It is drifting north about 15 kilometers per year. The Earth’s axial tilt is the same thing that causes the different seasons on Earth.
The Arctic Circle passes through seven countries that have a considerable portion of land within the Arctic Circle. The countries are the United States of America, Greenland, Canada, Russia, Norway, Sweden, and Finland. Iceland has a tiny region – less than one square km – inside the Arctic Circle. Some areas within the Arctic Circle include Lapland Province in Finland; Yukon, the Northwest Territories, and part of Nunavut in Canada; Davis Strait in the Atlantic Ocean; the Island of Grimsey, which is part of Iceland; and the Greenland and Norwegian Seas in the Atlantic Ocean. The Arctic Circle is also a popular tourist site. People travel from different parts of the world to experience the region. Many places in the Arctic Circle also offer tours; Alaska has quite a few tours, although you can also find them in other countries. Some of these involve hiking around the Arctic Circle region during the summer.
The summer solstice occurs once a year, and there is also a winter solstice each year. During both solstices, the tilt of the Earth’s axis is at its extreme either toward or away from the Sun. The tilt of the Earth does not actually change – it stays at 23.5° – however, the Earth also orbits the Sun causing different regions to be exposed to varying degrees of sunlight.
The word “solstice” has its roots in Latin from the words for “sun” and “to stand still.” This is because during the solstices, the Sun appears to stand still, and then it starts moving in the opposite direction in our sky. It begins to get lower in the sky, and the length of daylight starts getting shorter in the Northern Hemisphere.
In addition to the two solstices, there are also two equinoxes, which is where the days are of equal length at the equator. The tilt of the Earth is also responsible for the change in seasons we experience. During the summer solstice, the Suns is directly over the Tropic of Cancer.
The summer solstice is the longest day of the year – the longest time there is daylight – in the Northern Hemisphere. It is the opposite in the Southern Hemisphere however with the winter solstice being the longest day of the year. The exact date of the summer solstice moves around somewhat because of the way years are set up in the Gregorian calendar. For example, it fell on June 20th in 2000. Usually, however, it is on June 21st.
In some cultures, the solstices, and the equinoxes, represent the start of the seasons while they are the midpoint in other cultures. The summer solstice is the beginning of summer in America. The summer solstice has long been a time for celebration for many different cultures. Midsummer was a holiday celebrated in various European cultures.
Traditionally, Midsummer’s Day falls on June 24th, several days after the actual solstice. The Midsummer celebration of the ancient Gauls was known as the Feast of Epona. In China, the summer solstice celebration represented yin, earth, and the feminine while its opposite – the yang – was celebrated during the winter solstice.
Germanic, Slav, and Celtic tribes in Europe used to celebrate Midsummer with huge bonfires. Jumping through the fire was supposed to grant protection to people and bring love. The bonfires were also supposed to lend their power to the Sun, which would begin to wan as winter approached.
Universe Today has articles on the shortest day of the year and the declination of the Sun that will help you learn more about the solstices and seasons.
If you are looking for more information, About.com has a number of good articles on the summer solstice and Science World has some great articles and resources.
Astronomy Cast has an episode on Earth you will want to check out.
[/caption]
An astrolabe is an ancient tool used in solving problems that involve time and the position of the Sun and stars. Astrolabes can be used in timekeeping, surveying, geography, and astronomy to name a few disciplines. One of its most well-known uses is navigation. Using an astrolabe, you can determine how the sky looked at a certain point in time at a specific place. Since it really is a visible map of the sky, it has proven extremely helpful in astronomical equations.
The astrolabe was invented sometime around 200 BC, and the Greek astronomer Hipparchus is often credited with its invention. A number of Greek scholars wrote in-depth treatises and texts on the astrolabe. Eventually, the tool was introduced to scholars in the Islamic world. They soon started using the instrument, mainly for navigation, and wrote many texts on the instrument themselves. Texts were also written on the subject in India, showing the extent to which this tool was used around the world.
The astrolabe is constructed of a hollow disk that is known as the “mater.” The mater can hold several flat plates that are known as “tympans” or “climates.” Each tympan is made for a specific latitude. The mater is marked indicating hours, degrees, or both measurements. The rete is the actual map of the ecliptic plane and has several pointers to indicate the brightest stars. You can think of the rete as a star chart. Often, different scales are engraved on the back of the mater to help in calculations. The engravings differed, and some of them included trigonometric scales and a calendar to convert between the day of the month and the position of the Sun according to the astrolabe. The alidade is attached to the back of the astrolabe. The alidade is used to take a star’s altitude.
The first universal astrolabe was invented by the Islamic scholar Abu Ishaq Ibrahim al-Zarqali. Unlike its predecessors, this astrolabe could be used at any location around the world instead of only at a specific latitude.
There are a number of astrolabe collections around the world, and you can still purchase astrolabes from a variety of locations. A later variation of the astrolabe is the spherical astrolabe, which looks like a sphere surrounded by a number of rings. The spherical astrolabe was also used in astronomy. The astrolabe is a predecessor of the sundial, which is still common today as an ornament in many gardens.
Universe Today has a more in-depth article on the armillary sphere and one on ancient astronomy.
For more information on astrolabes, you may want to check out astrolabes and the mariner’s astrolabe.
[/caption] The Pyramids on Mars are hills or mountains on the surface of Mars that, from a low resolution image, have near-perfect symmetry resembling that of the Egyptian pyramids. These formations are found in the Martian region known as Cydonia, an albedo feature that gained celebrity-like attention in the 1970s.
Some of the images captured of the Martian surface by the Viking Missions in the 70’s showed a formation that closely resembled a humanoid face. E.T. aficionados immediately interpreted this as a structure built by intelligent lifeforms like ours. More photographs of the region (Cydonia) revealed pyramid-like structures.
One of them, the D&M pyramid had a near-perfect symmetry. Since the pyramids were located near the “Face on Mars”, speculations regarding its alien origins gained more followers. According to advocates of the theory, the Face on Mars may have been constructed by inhabitants of the nearby city a.k.a. the Pyramids on Mars.
They even pointed out the peculiar smoothness of the wide region beside the Pyramids on Mars, which may have been a vast body of water such as an ocean. The proximity of the ‘city’ to a large body of water is typical of most inhabitants who would naturally want to be near a huge source of natural resources and a medium for travel.
This fascinating theory or story later on subsided when much higher resolution photos from later expeditions, one in April 5, 1998 and another in April 8, 2001, revealed the Face on Mars as nothing more than a mesa, an elevated piece of land with a flat top and steep sides. Mesas can be found in the southwestern region of the US.
You can also find them in South Africa, Arabia, India, Australia, and of course, Spain. The term ‘mesa’ is actually derived from the Spanish word that means ‘table’. Mesas look pretty much like giant tables rising above a surrounding plain.
The sharper images showed that the top of the mesa did not resemble a face at all. As for the Pyramids on Mars, such geological formations can be found here on Earth. They’re usually formed through the action of ice in glaciation or frost weathering.
Some good examples of such formations here on Earth are Switzerland’s Matterhorn, USA’s Mount Thielsen, Scotland’s Buachaille Etive Mòr, and Canada’s Mount Assiniboine.
We have some related articles here that may interest you:
[/caption]
A black dwarf is a white dwarf that has cooled down to the temperature of the cosmic microwave background, and so is invisible. Unlike red dwarfs, brown dwarfs, and white dwarfs, black dwarfs are entirely hypothetical.
Once a star has evolved to become a white dwarf, it no longer has an internal source of heat, and is shining only because it is still hot. Like something taken from the oven, left alone a white dwarf will cool down until it is the same temperature as its surroundings. Unlike tonight’s dinner, which cools by convection, conduction, and radiation, a white dwarf cools only by radiation.
Because it’s electron degeneracy pressure that stops it from collapsing to become a black hole, a white dwarf is a fantastic conductor of heat (in fact, the physics of Fermi gasses explains the conductivity of both white dwarfs and metals!). How fast a white dwarf cools is thus easy to work out … it depends on only its initial temperature, mass, and composition (most are carbon plus oxygen; some maybe predominantly oxygen, neon and magnesium; others helium). Oh, and as at least part of the core of a white dwarf may crystallize, the cooling curve will have a bit of a bump around then.
The universe is only 13.7 billion years old, so even a white dwarf formed 13 billion years ago (unlikely; the stars which become white dwarfs take a billion years, or so, to do so) it would still have a temperature of a few thousand degrees. The coolest white dwarf observed to date has a temperature of a little less than 3,000 K. A long way to go before it becomes a black dwarf.
Working out how long it would take for a white dwarf to cool to the temperature of the CMB is actually quite tricky. Why? Because there are lots of interesting effects that may be important, effects we cannot model yet. For example, a white dwarf will contain some dark matter, and at least some of that may decay, over timespans of quadrillions of years, generating heat. Perhaps diamonds are not forever (protons too may decay); more heat. And the CMB is getting cooler all the time too, as the universe continues to expand.
Anyway, if we say, arbitrarily, that at 5 K a white dwarf becomes a black dwarf, then it’ll take at least 10^15 years for one to form.
One more thing: no white dwarf is totally alone; some have binary companions, others may wander through a dust cloud … the infalling mass generates heat too, and if enough hydrogen builds up on the surface, it may go off like a hydrogen bomb (that’s what novae are!), warming the white dwarf quite a bit.
