0
Active contributors today

## What's the Earth's "absolute" speed? i.e. in relation to the central Sun, the first-order star, or related to the Universe known center of mass...

A08
Featured 1 year ago

Velocity is always stated with respect to a reference point. It is a relative characteristic of an object. As such the question, though appears simple is meaningless in the present form.

#### Explanation:

What do we mean when we say that a car is traveling at $90 k m p h$? We imply that the car travels $90 k m$ across the Earth in one hour. Remember that we ignore the fact that the Earth itself is moving.

We assume that the Earth is our reference point. We live on earth and it is the center of our world. However, we discovered hundreds of years ago that Earth is not at the center of our Solar System. It moves in an elliptical orbit around the Sun.

• We can assess How fast does the Earth move around the Sun? We can figure this out with simple geometry and obtain that its speed around the Sun of about $1.07 \times {10}^{5} k m p h$.
• Quite recently we discovered that our the Solar System is actually nearer to the edge of galaxy and orbiting around the galactic core.

By measuring the speed of other galaxies with which these move towards or away from us, we assess our own orbital speed to be about $8.28 \times {10}^{5} k m p h$. But we can’t just add this to Earth’s speed around the Sun, as we’re moving in an ellipse.

Perhaps we can say that Earth’s speed around the galaxy is somewhere between $7.21 \times {10}^{5} k m p h$ and $9.35 \times {10}^{5} k m p h$ depending on a particular day of the year.

• Then we discovered that the Milky Way galaxy is not the centre of the Universe. Instead, it is just one in a cluster of galaxies, known as the Local Group. Relative to the centre of this group, the Milky Way travels at about $1.44 \times {10}^{5} k m p h$.
• Now The Local Group cluster is part of a larger structure made of all the neighbouring clusters called The Local Supercluster. Relative to which, our local Group moves at about $2.16 \times {10}^{6} k m p h$.

Next$-$ with the Local Supercluster’s speed we run into a problem. We haven’t yet seen what larger structure the Local Supercluster might be part of, which could be used as a reference point.

Map of our corner of the Milky Way galaxy. The Sun is located in the Orion Arm - a fairly minor arm compared with the Sagittarius Arm, which is located closer to the galactic center.

## Is the angle of the axis that the earth rotates on created by or affected by the sun?

David B.
Featured 1 year ago

Although the angle of the Earth's axis of rotation is not created by the sun, it is affected by the sun's gravity causing it to precess.

#### Explanation:

The angle of the Earth's axis of rotation is not created by the sun. It is a result of the residual angular momentum of the materials that coalesced to create the planet, and other events since that time, such as collisions, etc. The planets of the solar system have a wide range of angles and rotation directions:

The angle of the axis is affected by the sun, through a process known as precession . This precession is caused by the torque applied to the planet by the sun's gravity.

This causes the direction of the axis to move in a circle when viewed by an observer on the Earth. To the Earth-bound observer, the axis of rotation is viewed as the direction of the pole. The following picture shows how the north pole has shifted position through our view of the stars through the years (-2000 = 200 B.C., +2000 = 2000 A.D.). Right now, at 2016 A.D. the north pole points very near the star Polaris which is at the end of the handle of the Little Dipper .

## How does light affect the universe?

Gió
Featured 11 months ago

I can think of two main effects: Energy and Pressure.

#### Explanation:

Light carries Photon energy proportional to its frequency $f$ in the form given by Einstein's relationship (with a constant $h$):

$E = h f$

This energy will produce effects when interacting, say, with the components of a celestial body (planet, comet, even dust) promoting chemical reactions between elements and the possible formation of new compounds.

Another interesting effect is the Radiation Pressure associated with the propagation of electromagnetic radiation; basically, light can...push...object!
You can see this effect observing the direction of the comets' tail when travelling near the Sun: the plume of particles forming the tail of the comet is pushed away by the Sun's radiation in a radial direction from the Sun!

This pressure will affect clouds of dust and gas (as a current in a river or lake), possibly promoting local condensation of matter to create nuclei for the future formation of stars (the small aggregates of matter will now have a sizeable gravitational force able to further attract matter around them).

Hope it helps; it is the best I could think of.

## What started the Big Bang? What was there before it? What is some evidence for it? Why do some people not agree?

Ricardo A.
Featured 11 months ago

#### Explanation:

We have, however many hypotheses that could explain it, such as string theory or m-theory, the problem we have right now is that all the predictions these ideas make about the universe are impossible to test with our current technology. You see, all scientific models make predictions and we can prove or disprove them by going out and making observations that confirm or deny that model.

• What was there before it?

Same as above, we have models that could explain it, but the observations are beyond our tech so far.

• What is some evidence for it?

In the 1920s Edwin Hubble (the telescope was named after him) discovered that all galaxies are flying away from us, and the further away a galaxy is from us the faster it is going away from us. This proved the Universe was expanding. Meaning it must have been smaller early on. This begat the Big Bang Theory.
There are many cosmological observations that corroborate this, and one of the best, which was predicted by the theory itself, is the Cosmic Microwave Background.

• Why do some people not agree?

Overall the school system has done a poor job of communicating the science to the people. The media also doesn't help as it is sensationalist and misrepresents the issues most of the time, leading to people distrusting science. Religion also plays a part in it as science disproves some of the stuff written in their holy books, so they (true to their doctrines) truest blind faith over knowledge.

## Why was Pluto downgraded to a dwarf planet?

Phillip E.
Featured 6 months ago

Pluto was downgraded from planet to dwarf planet because the definition of a planet was changed.

#### Explanation:

When Pluto was first discovered it was given the status of being the ninth planet.

Since then, other bodies have been discovered in the asteroid belt and beyond Neptune which arguably should be planets if Pluto is a planet.

There are three conditions which must be met to be a planet.

First is must be roughly spherical in shape. Most planets are shaped like a squashed sphere with an equatorial bulge.

Second it must be in orbit around the Sun.

If a body meets these two conditions it is a planet of a dwarf planet. Pluto and other bodies are dwarf planets using theses rules.

Thirdly the body must have cleared its orbit of other bodies. Planets are formed from a disc of protoplanetary bodies orbiting the Sun. These bodies collide and clump together to form a planet. For a body to be a true planet all of theses bodies must have either become par t of the planet or formed a moon of the planet.

Pluto doesn't meet the third condition as it hasn't cleared its orbit of other bodies. Hence the decision was made to downgrade Pluto to a dwarf planet.

Some people, myself included, still regard Pluto as the ninth planet from its historical context. In fact the NASA DE430 data which can be used to calculate the positions of the Sun, Moon and planets still includes data for Pluto.

## What is the relationship between longitude of ascending node and argument of perihelion?

Phillip E.
Featured 3 months ago

Longitude of ascending node and argument of perihelion are two of the six orbital elements required to describe an orbit.

#### Explanation:

The orbit of a planet, moon or other body requires six parameters to describe it. These are know as orbital elements or Keplerian elements after Johannes Kepler who first described orbits with his three laws.

The first two elements and the eccentricity e and semi-major axis distance a which describes the shape of the ellipse. Kepler's first law states that orbits are ellipses.

To describe the other elements we need a frame of reference. The plane of the ecliptic is the plane of Earth's orbit. All orbits are measured relative to this.

We also need a direction which is 0 degrees in the plane. This is the Vernal Equinox. The Vernal Equinox is the moment when the Sun crosses the equator heading North which occurs around 20 March. The direction from the centre of the Earth to the point where the Sun crosses the equation is the reference direction. As the equinoxes precess, an epoch is defined. J2000 is often used. It is the direction of the Vernal Equinox on 1 January 2000 at 1200.

The inclination i is the angle the orbit makes to the ecliptic. For Earth it is always 0 degrees.

The longitude of ascending node $\Omega$ is the angle from the Vernal Equinox to the point where the orbit crosses the ecliptic heading North - the ascending node.

The argument of perihelion $\omega$ is the angle from the longitude of ascending node to the perihelion.

Finally the true anomaly $\nu$ is the angle the planet makes from perihelion to its position at a particular time.

So, the longitude of the ascending node defines the direction in which the orbit intersects the ecliptic. The argument of perihelion defines the angle from the direction of the ascending node to the direction of perihelion, the closest point to the body being orbited around.

##### Questions
• · 3 hours ago
• · 4 hours ago · in Astronomy Basics
• · 7 hours ago · in The Earth
• · 7 hours ago · in The Earth
• · 8 hours ago · in The Planets
• 9 hours ago · in The Sun
• · 9 hours ago · in Astronomy Basics
• · 13 hours ago
• · 17 hours ago · in The Earth
• · Yesterday
• · Yesterday · in The Earth
• · Yesterday · in The Big Bang
• · Yesterday
• · 2 days ago
• · 2 days ago
• · 2 days ago · in The Earth
• · 2 days ago · in The Earth
• · 3 days ago
• · 3 days ago