[Physics Class Notes] on Distances to the Stars Pdf for Exam

Distances to the stars were first determined through an approach known as trigonometric parallax, a method still implemented for the nearby stars. To measure the distance to nearby stars, astronomers observe an object’s stellar parallax, which is the apparent shift of an object relative to some distant background. Parallax is the only direct method for measuring stellar distances.

Taking the radius of the Earth’s orbit into consideration as a baseline, the distance of the star can be measured from the parallactic angle, p. However, if p = 1″ is one second of arc, then the distance of the star is 206,265 times the distance from Earth to the Sun in light-years.

The nearest star to Earth is Proxima Centauri, which is at the distance that equals 4.24 light-years. Proxima Centauri is a part of Alpha Centauri. The Alpha Centauri distance to the Sun is 4.37 light-years.

Thus, trigonometric parallaxes are functional for only the nearest stars to Earth, which lie within a few thousand light-years. For more distant stars, indirect methods are implemented to observe and measure; most of them depend on comparing the star’s intrinsic brightness with its apparent brightness.

What are the Earth’s Closest Stars?

There are only three stars, Alpha Centauri, Procyon, and Sirius, among the nearest 20 and amid the brightest 20 stars. Most of the Earth’s stars remain relatively nearby and are dimmer than the Sun and also remain invisible if viewed without the telescope’s aid. However, the Earth’s closest star is Proxima Centauri, about 93 million miles away. The most luminous stars close to Earth can be observed at great distances, while the faint ones can be seen if they are relatively close to the Earth.

The brightest and nearest stars fall roughly into three categories: (1) Giant and Supergiant stars that possess sizes of tens or even hundreds of solar radii and extremely low average densities. (2) Dwarf stars hold sizes ranging from 0.1 to 5 solar radii, and their masses range from 0.1 to about ten solar masses. (3) White dwarf stars have masses comparable to that of the Sun but have their average densities hundreds of thousands of times greater than that of the water.

What is an Astronomical Unit?

An Astronomical Unit (AU) represents the mean distance between the Earth and Sun. An AU (the distance from Earth to Sun in meters) is approximately 93 million miles or 149.8million km. It’s about eight light minutes. However, the Earth’s orbit around the Sun isn’t a perfect circle. Therefore, the Sun distance to Earth changes throughout the year. The average distance from Earth to Sun in light years, in AU, is one light-year is equal to 63,240 AU. Thus, it can be concluded that one astronomical unit is the approximate mean distance of Earth and Sun., where the distance from Earth to Sun in meters is about 150 million km or 93 million miles, or eight light minutes.

The Distance of Planets from Sun

Our solar system comprises the Sun, eight planets, moons, several plutoids, an asteroid belt, meteors, comets, etc. Eight planets orbit around the Sun and the distance of the planets from the Sun are influenced by several factors. Planets near the Sun receive more energy and have a warm or hot temperature, while the planets that are further away from the Sun receive less energy, and their weather is generally more relaxed. 

The distance of the planets from the Sun increases from Mercury to Neptune or Pluto. The distance from Earth to Sun is called an Astronomical unit, or AU, to measure distances throughout the solar system. The current distance between Earth and Sun is 149.83 million km. 

Distance Between Moon and Sun

Since the Moon orbits the Earth and the Earth orbits the Sun, the average sun distance to Earth is the same as the distance between Moon and Sun. On average, the Moon and Sun’s distance is about 150 million kilometers (93 million miles). This distance of Earth and Sun is so considerable that it takes light eight minutes to reach the Earth and its satellite which means that if the Sun stopped shining, there would be a void of eight minutes. When the Moon is the farthest away, it’s 252,088 miles away from the Sun, which means 32 piles of Earth away. When it’s closest, the Moon is 225,623 miles out, between 28 and 29 Earths.