My Science School

The farther you get away from the Sun, the cooler you get. So let’s take a look at those planets that sit between Earth and the Sun: Mercury and Venus.

Since Mercury sits closest to the Sun, it must be the hottest planet. Right? That only makes sense, doesn’t it? After all, Mercury receives more sunlight per square foot than any other planet in the solar system. Wrong! Venus is actually the hottest planet in the solar system.

On a hot day on Mercury, the temperature can rise to over 700 ºF. That’s hot! You’d definitely need plenty of sunscreen there. A hot day on Venus, however, is even hotter. How much so? The highest temperatures on Venus exceed 900 ºF. Yikes! Now that’s a scorcher, for sure.

Most friends are probably wondering why Venus is hotter than Mercury. After all, it’s farther away from the Sun. The answer lies in the atmosphere. 

Mercury is small and sits closest to the Sun. It also moves very quickly around the Sun. For these reasons, it doesn’t have an atmosphere. When the Sun’s rays hit Mercury, they just bounce off into space. There’s nothing to reflect them back toward the planet and retain their heat.

Venus, on the other hand, has a very thick atmosphere. Its atmosphere is actually over 90 times denser than Earth’s atmosphere. It’s also made up mostly of carbon dioxide, a greenhouse gas. Venus’s atmosphere acts like a one-way door. It lets in solar radiation, but it doesn’t let it back out.

This creates oven-like conditions on the surface of Venus. Because of this intense heat, no water can be found there. Moreover, carbon dioxide is a noxious gas. It creates raging winds that blow constantly across the surface of the planet. This gives it one of the harshest environments you’re likely to find in the entire solar system. Earth and Venus are sometimes called “sister” planets because of their similar sizes. But in most other ways, they couldn’t be more different.

Before scientists could see Venus with the help of unmanned probes and space telescopes, many of them thought Venus was a lush, tropical paradise. The truth is that it’s a barren rock that looks like Earth’s Moon. Its clouds appear yellowish because of the presence of sulfur dioxide alongside the huge amounts of carbon dioxide.

Credit : Wonderopolis 

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Just to be clear, this answer to ‘which planet has the longest day’ is based on this criteria: a planets day is how long it takes it to complete one rotation on its axis. This is also referred to as its rotational period. So, Venus has the longest day of any planet in our solar system. It completes one rotation every 243 Earth days. Its day lasts longer than its orbit. It orbits the Sun every 224.65 Earth days, so a day is nearly 20 Earth days longer than its year.

Now, back to why the Venusian day is longer than its year. Venus is closer to the Sun; therefore, its orbit takes a shorter period of time than its rotation upon its axis. The planet also rotates in retrograde. That means it spins in the opposite direction of the Earth. If you were standing on Venus, you could see the Sun rise in the West and set in the East.

A manned Venus flyby mission was proposed in the late 1960s. The mission was planned to launch in late October or early November 1973, and would have used a Saturn V rocket to send three men. The flight would have lasted approximately one year. The spacecraft would have passed approximately 5,000 km from the surface about four months into the flight. There have been several unmanned probes and flybys of the planet, including MESSENGER and the Venus Express. Future proposed missions include the BepiColombo, Venus InSitu Explorer, and the Venera-D.

Credit : Universe Today 

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Imagine a line passing through the center of Earth that goes through both the North Pole and the South Pole. This imaginary line is called an axis. Earth spins around its axis, just as a top spins around its spindle. This spinning movement is called Earth’s rotation. At the same time that the Earth spins on its axis, it also orbits, or revolves around the Sun. This movement is called revolution. A pendulum set in motion will not change its motion, and so the direction of its swinging should not change. However, Foucault observed that his pendulum did seem to change direction. Since he knew that the pendulum could not change its motion, he concluded that the Earth, underneath the pendulum was moving. An observer in space will see that Earth requires 23 hours, 56 minutes, and 4 seconds to make one complete rotation on its axis. But because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is actually 24 hours. At the equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles the movement speed is nearly nothing.

For Earth to make one complete revolution around the Sun takes 365.24 days. This amount of time is the definition of one year. The gravitational pull of the Sun keeps Earth and the other planets in orbit around the star. Like the other planets, Earth’s orbital path is an ellipse so the planet is sometimes farther away from the Sun than at other times. The closest Earth gets to the Sun each year is at perihelion (147 million km) on about January 3rd and the furthest is at aphelion (152 million km) on July 4th. Earth’s elliptical orbit has nothing to do with Earth’s seasons. During one revolution around the Sun, Earth travels at an average distance of about 150 million km. Earth revolves around the Sun at an average speed of about 27 km (17 mi) per second, but the speed is not constant. The planet moves slower when it is at aphelion and faster when it is at perihelion. The reason the Earth (or any planet) has seasons is that Earth is tilted 23 1/2oon its axis. During the Northern Hemisphere summer the North Pole points toward the Sun, and in the Northern Hemisphere winter the North Pole is tilted away from the Sun.

Credit : Lumen Learning 

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Of the terrestrial (rocky) planets of the inner solar system, neither Mercury nor Venus have any moons at all, Earth has one and Mars has its two small moons. In the outer solar system, the gas giants Jupiter and Saturn and the ice giants Uranus and Neptune have dozens of moons. 

Jupiter's menagerie of moons includes the largest in the solar system (Ganymede), an ocean moon (Europa) and a volcanic moon (Io). Many of Jupiter's outer moons have highly elliptical orbits and orbit backwards (opposite to the spin of the planet). Saturn, Uranus and Neptune also have some irregular moons, which orbit far from their respective planets.

Saturn has two ocean moons – Enceladus and Titan. Both have subsurface oceans and Titan also has surface seas of lakes of ethane and methane. The chunks of ice and rock in Saturn's rings (and the particles in the rings of the other outer planets) are not considered moons, yet embedded in Saturn's rings are distinct moons or moonlets. These shepherd moons help keep the rings in line. Titan, the second largest in the solar system, is the only moon with a thick atmosphere.

In the realm of the ice giants, Uranus's inner moons appear to be about half water ice and half rock. Miranda is the most unusual; its chopped-up appearance shows the scars of impacts of large rocky bodies.

Neptune's moon Triton is as big as Pluto and orbits backwards compared with Neptune's direction of rotation.

Credit : NASA Science

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The earth has about 70 percent of water on its crust. It also has an abundance of oxygen thanks to its multilayered atmosphere made of several gasses. The moon neither has oxygen nor water. It weak atmosphere does not support the formation of oxygen. Hence it remains a barren and lifeless astral body. However, the possibilities of finding water and ice on the moon are being explored by humans through several studies now.

The moon has only a very thin atmosphere, so a layer of dust — or a footprint — can sit undisturbed for centuries. And without much of an atmosphere, heat is not held near the surface, so temperatures vary wildly. Daytime temperatures on the sunny side of the moon reach 273 degrees F (134 Celsius); on the night side it gets as cold as minus 243 F (minus 153 C).

The moon's gravity pulls at the Earth, causing predictable rises and falls in sea levels known as tides. To a much smaller extent, tides also occur in lakes, the atmosphere and within Earth's crust.

High tides refer to water bulging up from Earth's surface, and low tides when water levels drop. High tides occur on the side of the Earth nearest the moon due to gravity, and on the side farthest from the moon due to the inertia of water. Low tides occur between these two humps.

The pull of the moon is also slowing the Earth's rotation, an effect known as tidal braking, which increases the length of our day by 2.3 milliseconds per century. The energy that Earth loses is picked up by the moon, increasing its distance from the Earth, which means the moon gets farther away by 1.5 inches (3.8 centimeters) annually.

Credit : Space.com 

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Saturn has 82 moons. Fifty-three moons are confirmed and named and another 29 moons are awaiting confirmation of discovery and official naming. Saturn's moons range in size from larger than the planet Mercury — the giant moon Titan — to as small as a sports arena. The moons shape, contribute and also collect material from Saturn's rings and magnetosphere.

Including provisional moons, Saturn has 82 total possible moons, while Jupiter has 79. Gas giants like these planets are so large and have such strong gravitational fields, they're able to attract far more satellites than a planet, like say, Earth, with its one moon. And these numbers of moons will likely change in the future as astronomers continue observing Saturn and Jupiter and the many bodies that orbit them both. Jupiter may even overtake Saturn at some point in the future.

While Jupiter is known for its four large Galilean moons (so named because they were observed by Galileo with his 17th century telescope), Saturn has two moons that have drawn astronomers' attention: Enceladus and Titan.

Both Enceladus and Titan are ocean moons, meaning they have subsurface oceans of liquid water. Titan even has surface lakes, though these are composed of methane and ethane. Enceladus is an icy moon known for spraying huge plumes of water up through its atmosphere into space; during the Cassini mission, astronomers were able to sample these geysers and that's how they discovered the ocean underneath its icy crust.

Credit : How stuff works

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'There used to be a number of theories about how the Moon was made and it was one of the aims of the Apollo program to figure out how we got to have our Moon,' says Sara.

Prior to the Apollo mission research there were three theories about how the Moon formed.

Capture theory suggests that the Moon was a wandering body (like an asteroid) that formed elsewhere in the solar system and was captured by Earth's gravity as it passed nearby. In contrast, accretion theory suggested that the Moon was created along with Earth at its formation. Finally, according to the fission scenario, Earth had been spinning so fast that some material broke away and began to orbit the planet.

What is most widely accepted today is the giant-impact theory. It proposes that the Moon formed during a collision between the Earth and another small planet, about the size of Mars. The debris from this impact collected in an orbit around Earth to form the Moon.

Credit : Natural History Museum

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The sun is large enough that approximately 1.3 million Earths could fit inside. Want to check our math? The volume of the sun is 1.41 x 1018 km3, while the volume of Earth is 1.08 x 1012 km3. If you divide the volume of the sun by the volume of the Earth, you get that roughly 1.3 million Earths can fit inside the sun. However, this assumes that the Earths are squished together without leaving any empty space. Scientists estimate that if the Earths retained their spherical shape, only about 960,000 would fit because of wasted space in between the spheres.

Of course, the Sun is a fairly average sized stars. There are some enormous stars out there. For example, the red giant Betelgeuse has a radius of 936 times the radius of the Sun. That gives it hundreds of millions of times more volume than the Sun.

And the largest known star is VY Canis Majoris, thought to be between 1800 and 2100 times the radius of the Sun.

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The sun is a star, a hot ball of glowing gases at the heart of our solar system. Its influence extends far beyond the orbits of distant Neptune and Pluto. Without the sun's intense energy and heat, there would be no life on Earth. And though it is special to us, there are billions of stars like our sun scattered across the Milky Way galaxy. If the sun were as tall as a typical front door, the Earth would be the size of a U.S. nickel. The temperature at the sun's core is about 27 million degrees Fahrenheit.

The sun lies at the heart of the solar system, where it is by far the largest object. It holds 99.8% of the solar system's mass and is roughly 109 times the diameter of the Earth — about one million Earths could fit inside the sun. 

The surface of the sun is about 10,000 degrees Fahrenheit (5,500 degrees Celsius) hot, while temperatures in the core reach more than 27 million F (15 million C), driven by nuclear reactions. One would need to explode 100 billion tons of dynamite every second to match the energy produced by the sun, according to NASA.

The sun is one of more than 100 billion stars in the Milky Way. It orbits some 25,000 light-years from the galactic core, completing a revolution once every 250 million years or so. The sun is relatively young, part of a generation of stars known as Population I, which are relatively rich in elements heavier than helium. An older generation of stars is called Population II, and an earlier generation of Population III may have existed, although no members of this generation are known yet.

The sun was born about 4.6 billion years ago. Many scientists think the sun and the rest of the solar system formed from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed because of its gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form the sun.

The sun has enough nuclear fuel to stay much as it is now for another 5 billion years. After that, it will swell to become a red giant. Eventually, it will shed its outer layers, and the remaining core will collapse to become a white dwarf. Slowly, the white dwarf will fade, and will enter its final phase as a dim, cool theoretical object sometimes known as a black dwarf.

Credit : Space.com

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The speed of light is approximately 1,079,000,000 kilometers/hour (670,600,000 miles/hour). On average, the Sun is 150 million kilometers (93 million miles) away from Earth. This means that it takes a photon of light about 8 minutes and 20 seconds to travel from the Sun to Earth.

Objects in our universe are extremely far away. They’re so far away that kilometers or miles aren’t a useful measure of their distance. So we speak of space objects in terms of light-years, the distance light travels in a year. Light is the fastest-moving stuff in our universe. It travels at 186,000 miles per second (300,000 km/sec). And thus a light-year is 5.88 trillion miles (9.46 trillion kilometers).

But stars and nebulae – not to mention distant galaxies – are vastly farther than one light-year away. And, if we try to express a star’s distance in miles or kilometers, we soon end up with impossibly huge numbers. Yet miles and kilometers are what most of us use to comprehend the distance from one place on Earth to another. In the late 20th century astronomer Robert Burnham, Jr. – author of Burnham’s Celestial Handbook – devised an ingenious way to portray the distance of light-years in terms of miles and kilometers.

Credit : Earth Sky

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According to the World Meteorological Organization, Yuma (Arizona) is the sunniest place on earth. It has a total of 11 hours of sunlight in winter and up to 13 in summer. This means Yuma experiences an average of 4,015 hours of sunshine per year.

At first this sounds fantastic. But it really isn’t that pleasant, since its 90,000+ inhabitants have to combat an arid climate, typical of the Sonora desert, which it forms part of.

Rainfall does not exceed 200mm per year and temperatures exceed 40°C practically 100 days per year. It is a furnace that would leave you wishing for a winter’s rainy afternoon.

The wide-open spaces in and around Yuma lend themselves perfectly to outdoor adventures in the desert or on the Colorado River. Social distancing? No problem! Fresh air and nature? Lots of it! Sunny and warm weather? Undoubtedly, since Yuma is the Sunniest City on Earth, according to Guinness World Records.

If you want rugged outdoor adventure, Yuma's the perfect jumping-off spot to hundreds of square miles of wilderness in the Imperial, Kofa and Cibola National Wildlife Refuges.  Hiking, mountain biking, camping, bird watching, and learning more about desert plants and animals are all out there for exploring.

If in-town adventures are more to your liking, just steps from downtown, parklands next to the Colorado River are a gleaming necklace, studded with pearls of spacious and beautifully-tended attractions, monuments, beaches, and two must-see historic state parks. You can hike or jog on paved or woodchipped or dirt paths along the riverfront, and there are many family-friendly features such as a playground, beaches, and picnic ramadas. The East and West Wetlands are the pride of Yuma, having been restored to natural habitat from what had been a homeless camp and the city dump in the past century. Now a point of civic pride for local Yumans, the riverfront parks make it easy to experience Yuma naturally!

Credit : Visit Yuma

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An annular eclipse, though a rare and amazing sight, is far different from a total one. The sky will darken ... somewhat; a sort of weird "counterfeit twilight" since so much of the sun still shows. The annular eclipse is a subspecies of a partial eclipse, not total. The maximum duration for an annular eclipse is 12 minutes 30 seconds.

However, an annular solar eclipse is similar to a total eclipse in that the moon appears to pass centrally across the sun. The difference is, the moon is too small to cover the disk of the sun completely. Because the moon circles Earth in an elliptical orbit, its distance from Earth can vary from 221,457 miles to 252,712 miles. But the dark shadow cone of the moon's umbra can extend out for no longer than 235,700 miles; that's less than the moon's average distance from Earth.

So if the moon is at some greater distance, the tip of the umbra does not reach Earth. During such an eclipse, the antumbra, a theoretical continuation of the umbra, reaches the ground, and anyone situated within it can look up past either side of the umbra and see an annulus, or "ring of fire" around the moon. A good analogy is putting a penny atop a nickel, the penny being the moon, the nickel being the sun.

Credit : Space.com 

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It made history! On 24 September 2014, the Indian Space Research Organisation’s (ISRO) Mars mission, Mangalyaan, settled into its elliptical orbit around Mars as planned, with 40 kg of fuel to spare, 20 kg in excess of what was needed to complete its six-month planned mission!

Though over the next couple of months, the orbiter completed its mission objectives, it had enough fuel to remain operational, and its mission was extended. It continues to collect and transmit data to date, even on its seventh year in Mars orbit! Over this period, thanks to its autonomous functioning capabilities, Mangalyaan overcame an extended communications “blackout” in 2015 when Mars went out of the Earth’s sight behind the Sun in a solar conjunction, and a communications “whiteout” in 2016 when the Earth came in between the Sun and Mars with the solar radiation making it difficult for the spacecraft to receive signals from the Earth. Mangalyaan’s contribution to advancing the Indian space mission has been acknowledged in a unique way - a sketch of the spacecraft that features on the new Indian 2,000-Rupee note! It was also listed as one of the 25 best inventions of 2014 in Time magazine.

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Have you seen a film hero leap out of a moving car, and dash across the platform to board a running train? Don’t ever do it, because nothing can be more dangerous! For our spacecraft, they have no other choice. Because both their home and destination planets are racing around the Sun without ever stopping! To execute such a terrifying transit, different spacecraft use different manoeuvres. Mangalyaan did it in three phases - geocentric, heliocentric and areocentric phases.

In the first phase, Mangalyaan was carried by its rocket into an orbit around the Earth. Then by firing the spacecraft’s main engine in seven, carefully-planned stages, Mangalyaan’s orbit was made more and more elliptical, until it broke free of the Earth’s gravitational pull. The final firing launched Mangalyaan on a Sun-centric curved path to Mars, tangential to both planets. This space cruise stage from the Earth to Mars formed the second phase of the mission. The third phase began about ten months later with a precisely-timed manoeuvre, called Mars Orbit Insertion (MOI). The engines were fired once again to reduce the velocity of Mangalyaan just enough so that the gravitational field of Mars would pull the spacecraft into an orbit around it.

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The Mars Orbiter Mission (MOM), or Mangalyaan, was not just a scientific mission. It was also a chance to showcase the capabilities of Indian-made spacecraft, rockets and other instruments in the field of space technology!

As a technology demonstrator, Mangalyaan was to successfully cover all stages of an interplanetary journey - first go around the Earth in increasingly elliptical orbits, then cruise through space for the planned number of days, reach Mars and fall into an orbit around the planet, and continue orbiting it for the mission duration. The second goal of Mangalyaan was to image Mars, and collect data about its atmosphere and mineral composition. For this, Mangalyaan carried five payloads - Mars Colour Camera (MCC), Methane Sensor for Mars (MSM), Lyman Alpha Photometer (LAP), Mars Exospheric Neutral Composition Analyzer (MENCA), and Thermal Infrared Imaging Spectrometer (TIS).

While designing Mangalyaan, the Indian Space Research Organisation (ISRO) planned for all challenges it could foresee. Its engine was designed to restart smoothly after its ten-month space cruise.

Another aspect taken care of was the deep space communication system. The large distances separating the Earth and Mars mean that the Round-Trip Light Time, or RTLT (the time taken for a signal from Earth to travel to a spacecraft and back), will be anywhere between 6 and 43 minutes! So, it was also designed to independently manage many in-flight situations!

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