Astronomy telescope for beginners

astronomy telescope for beginners

Optical telescopes, which form images of faint and distant stars, can collect much more light from space than the human eye can. Optical telescopes are built in two basic designs.

  1. Refractors
  2. Reflectors

The heart of any telescope is its objective. The objective is a lens (in refractors) or mirror(in reflectors) whose function is to gather light from a sky object and form its image. The amount of light collected by the objective is called its light gathering power. Light gathering power is proportional to the area, or to the square of the diameter, of the collector. The size of a telescope, such as “6-inch” or “200-inch” refers to the diameter of its objective.

You can look at the image formed by the objective through and eyepiece, a variety of other ways. Your eye lens size is about 1/5 inch. A 6-inch telescope has an objective that is thirty times bigger than your eye lens. Its light gathering power is (30)2, or nine hundred times greater than your eye’s. So a star appears nine hundred times brighter with a 6-inch telescope than it does to your naked eye.

All stars appear brighter with telescopes than they do to your eye alone. All the extra starlight gathered by the telescope is concentrated into a single point. Using time exposure, the 200-inch telescope can photograph very faint stars down to nearly magnitude 24 (see frame 1.7). A star of that magnitude has about the same apparent brightness as a candle viewed from 10,000 miles away.

The Refracting telescope

The refracting telescope has a large lens (the objective) permanently mounted at the front end of the tube. Starlight enters this lens and is refracted, or bent so that it forms an image near the back of the tube.

The distance from this lens to the image is its focal length. You look at the image through a removable magnifying lens called ocular, or eyepiece. The tube keeps out scattered light, dust, and moisture.

Galileo Galilei first pointed refracting telescopes skyward in Italy in the seventeenth century. The largest instrument he made was smaller than 2 inches. Today refracting telescopes range in size from a beginner’s 2.4-inch (60-mm) version to the world’s largest, the 40-inch (12-cm) telescope at the Yerkes Observatory in Williams Bay, Wisconsin.

The reflecting telescope

The reflecting telescope has a highly polished curved glass mirror (the objective) mounted at the bottom of an open tube. When starlight shines on this mirror, it is reflected back up the tube to form an image at the prime focus.

You can place the photographic film at the prime focus to record the image, or you can use additional mirrors to reflect the light to another spot for viewing. The Newtonian reflector uses a small flat mirror to reflect the light through the side of the tube to an eyepiece. The cassegrain reflector uses a small convex mirror to reflect the light through a hole cut in the objective mirror at bottom of the tube.

Reflecting telescope range in size from a beginner’s 3-inch Newtonian reflector to the world’s largest the 236-inch (6-m) reflector in Caucasus mountains in the soviet union. The largest reflectors in the United States is the 200-inch (508-cm) Hate Telescope on Mount Palomar in California.

Telescopes are often described by both their objective size and f-number. The f-number is the ratio of the objective to its diameter. These specifications are important because the brightness, size, and clarity of the image produced by a telescope depend on this diameter and focal length of the objective. For example,”6- inch, f/8 reflector “ means the objective mirror is 6 inches in diameter and has a focal length  of 48 inches (8 times 6).

Image size is proportional to the focal length of the telescope’s objective. For example, a mirror whose focal length is 100 inches produces an image of the moon that measure almost 1 inch across. You know that the 200-inch mirror has a focal length of 660 inches, which is over times longer. Hence, it produces an image of the moon that is about six times bigger, or about 6 inches across.

Lenses and mirrors and from real images that are upside down. (A real image is formed by the actual convergence of light rays.) All stars except our sun are so far away that they appear as dots of light. The moon and planets appear as small disks. Since inverted images do not matter in astronomical work, nothing is done to turn them upright in telescopes.

Even if a telescope were of perfect optical quality, it would not produce perfectly focused image because of nature of light itself. A telescope’s resolving power is its ability to produce sharp, detailed image under ideal observing conditions. Resolving power is proportional to the diameter of the objective.

Starlight travels are straight lines through empty space. But when waves of starlight pass close to the edge of a lens or mirror, they spread out, in an effect called diffraction, and com to a focus at different spots. Because of diffraction, the image of a star formed by a lens or mirror appears as a tiny blurred disk surrounded by faint rings, called a diffraction pattern, instead of as a single point of light.

If two stars are close together, their diffraction patterns may overlap so that they look like a single star. Features such as moon craters and planet marking are also blurred by diffraction.

Resolving power indicates the smallest angle between two stars for which separate, recognizable images are produced. The resolving power of the human eye is about one minute of are (1’).

A telescope magnifying power is the ratio of the apparent size of an objective seen through the telescope compared its size seen by the naked eye. Telescopes magnify the angular diameter of objectives. Thus the images appear to closer than the object.

For example, to your naked eye the apparent size of the full moon is ½0, the same as an aspirin held at arm’s length. If the apparent size of the moon increases twenty times (so that it looks 100 in diameter When you view it through your telescope, then the magnifying power is 20, written 20X.

What does statistics mean

what is statistics

What is Statistic?

  •  Statistics is a way to get information from data.
  •  Statistics is the study of the collection, organizing, analysis, interpretation and presentation of data.

Two Kinds of Statistics

01.Descriptive Statistics

Descriptive statistics consists of methods for organizing, summarizing, and presenting data in a convenient and informative way. These methods include graphical techniques and numerical techniques.

02.Inferential Statistics

Inferential statistics consists of methods for drawing conclusions about a population based on information obtained from a sample of the population.

Population and Sample


The population is the collection of all individuals, items, or data under consideration in a statistical study.


The sample is a part of the population from which information is collected.

Census and Survey


A census is a study of the entire population. We collect information from the whole population.


A survey is a study of a sample which was derived from the population. We collect information from a sample.

Parameter and Statistic


A parameter is a number/numerical quantity that describes a characteristic of the population.


A statistics is a number/numerical quantity that describes a characteristic of a sample.

Variables and Data

Types of variables


A variable is a characteristic of each person or thing of the population or a characteristic that varies from one person or thing to another. There are several types of variable as below.

Types of variables

Types of Data

Data are values of a variable. There are two ways to classify data as below.

Types of Data

Qualitative Data

Qualitative data are obtained by observing values of a qualitative variable. They are most often nonnumerical.

Quantitative Data

Quantitative data are obtained by observing values of a quantitative variable. They are inherently numerical.

Discrete Data

Discrete data are obtained by observing values of a discrete variable. These data can take on only certain values. These values are often integers or whole numbers.

Nominal Data

Nominal data are categorical data and numbers that are simply used as identifiers or names.

Ordinal Data

Ordinal data represent an ordered series of relationships or rank order. Here the order of the values is important and significant, but the differences between each one are not really known.


Interval data are numeric data in which we know not only the order but also the exact differences between the values. Here’s the problem with interval data: they don’t have a “true zero.”


Ratio data tell us about the order, they tell us the exact value of units, and they also have an absolute zero–which allows for a wide range of both descriptive and inferential statistics to be applied.

Classification Data Based on Who Collected the Data

Primary Data

Data collected by the investigator himself/ herself for a specific purpose of addressing the problem at hand. (Questionnaires, telephone interviews, face to face interviews).

Some Advantages of Using Primary Data

  1. The investigator collects data specific to the problem under study.
  2. There is no doubt about the quality of the data collected (for the investigator).
  3. If required, it may be possible to obtain additional data during the study period.

Some Disadvantages of Using Primary Data

  1. The investigator has to contend with all the hassles of data collection.
  2. Ensuring the data collected is of a high quality.
  3. Cost of obtaining the data is often the major expense in studies.

Secondary Data

Data collected by someone else for some other purpose (but being utilized by the investigator for another purpose).

Some Advantages of Using Secondary Data

  1. There are no any hassles of data collection.
  2. It is less expensive.
  3. The investigator is not personally responsible for the quality of data (“I didn’t do it”).

Some Disadvantages of Using Secondary data

  1. The investigator cannot decide what is collected.
  2. One can only hope that the data is of good quality.
  3. Obtaining additional data about something is not possible (most often).

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Best books on Macroeconomics

Best books on Macroeconomics

What is Macroeconomics?

The study of economics involving phenomena that affects the entire economy, including inflation,economic decline, unemployment, economic growth, price levels, and the relationships between all of these.  Where macroeconomics looks it how household and businesses make decisions and behave in the marketplace and macroeconomics looks in a big picture. It analyses the entire economy. We live in a complex and inter-connected world. The economy is affecting to all. Most of us depend on the economy to provide job or business opportunities so we can make money to buy the goods and services we need to survive in function modern society.
The study of macroeconomics allows us to better understand what makes our economy growth and what makes it contract. A growing economy provides opportunities for a better life while a contracting economy disasters for most everyone. Macroeconomics provides the analysis for proper policy making  so we can develop the nature best economy possible. Macroeconomics focuses on three broad areas and the relationship between them. These three concepts affect all participants  in economy including consumers workers producers and government.

Economic Output

Macroeconomics studies the national output or income of a country. The National economic output is the total value of all good and services produced in an economy during a specific time period. Economists measure national output by calculating  the gross domestic product (GDP) which is the market value of final goods and services an economy produced during  a specific period of time. Economists will use the term real GDP which is GDP valued at a constant price level to compare the current output with past output. This comparison will tell you the economy is growing to stagnate or it’s contracting. The basic model that used in macroeconomics to study economic fluctuations is the model of aggregate demand and aggregate supply. The model involves two variables. The economy output which measures by real GDP and economy overall price level measured by a price index. Usually the GDP deflator or CPI. You can plop the general price level in an economy on the vertical axis of the graph and the quantity of the output on the horizontal axis. The aggregate supply curve is upward sloping and the short run but vertical in a long run. The aggregate demand curve is downward sloping. Economic output in the price level will move towards the point where aggregate supply equal to aggregate demand. Fluctuation in economics output generally called by one of two things.
01. Fluctuation can occur when the aggregate demands shifts.
If the aggregate demand curve shifts to the left output and prices will decline. IF the curve shifts to the right output and prices will rise.
02. Economic fluctuations may be caused by a shift in aggregate supply.
A right shift in the aggregate supply curve means that the quantity of goods and services supply will increase at a particular price level. If a short-term aggregate supply shifts to the left output will fall and prices will rise. This is called stagflation.


Macroeconomic study employment and what leads to unemployment which is the percentage of people who are not working but want to work. Unemployment doesn’t economic reality. There is a natural rate of unemployment that in an economy normally experiences even one in an economy is stable. Cyclical unemployment is a deviation from the natural unemployment rate that is usually caused by fluctuations in the business cycle. People transitioning between jobs cause frictional unemployment and structural unemployment which unemployment that occurs when there are jobs available. but unemployed workers don’t have the skills to qualify for them. Economists measure unemployment through calculating the unemployment rate and the labor participation rate. The unemployment rate measures the percentage of people in the labor force that are unemployed. Labor participation rate measures the percentage of people that are eligible to work but are not working.

Inflation and Deflation

Inflation is a rise in the general price level of an economy and Deflation is a decline in the general price level of an economy
Money supply is correlated to Inflation and Deflation. According to the quantity theory of money, the quantity of money available in an economy will determine the general price level and the growth rate in the quantity of money will determine the rate of inflation. As the money supply increases, inflation will increase.

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Recommended books.

Video books

Understanding Macroeconomics for University and Business
Basics of Macroeconomics

E-books and Hardcover

Macroeconomics: Principles, Problems, & Policies

Principles of Macroeconomics (Mankiw’s Principles of Economics)