Radio Astronomy: Whats at the Center of the Milky Way

What's in Milky Way ... Besides Us?

What is the Milky Way Galaxy?	Where are we in it?
Why, if there is a million solar mass Black Hole in the center, haven't you seen it?	Where is the center of our galaxy anyway?

We answer questions in the lessons below. These lessons designed and tested by high school teacher Rob Welsh and astronomer Glen Langston.

The lessons use a minimum of mathmatics. The grade level and skill requirements are given for each lesson.

Answer to the first Question: The Milky Way Galaxy is a "flat-ish" disk of stars and gas that rotates about its center. The Galatic Center is visible every night in the summer in the lower 48 United States. But it's hidden by clouds of dust, so that almost no one notices it. With a radio telescope, the Black Hole (BH) and star forming regions near the center are incredibly bright, as is shown in the zoomed color picture above. In the picture above, the black and white dots are stars and the colored stripe is a radio map of the galatic plane. The BH at the Galactic center is in the middle of the image.

The Sun is one of over 100 billion stars in a vast collection of stars known as The Milky Way. But there is more than stars in our galaxy. There are vast clouds of gas where stars are born and very dense objects called pulsars.

Lesson 1: The Discovery of the Milky Way
The Milky Way Galaxy is a vast collection of over 100 billion stars. Our Sun is placed about two-thirds away from the center. It has taken almost four hundred years to understand our location in the Universe. In this lesson, you'll learn about advances in or understanding of the galaxy through history. There is no mathematics in this lesson, but plenty of links to other sites, which give more detailed information. The lesson ends with questions to be answered based on your understanding of each astronomer's contribution to our understanding of the Milky Way.

Lesson 2: Introduction to Image Processing
In the second lesson, you will analyze images taken by the Green Bank Earth Station. You will learn to use the image processing software program Sky Image Processor (SIP). The result of your analysis will be radio brightness measurements taken on a group of different radio sources. There is minimal mathematics required to perform this exercise.

Lesson 3: Measuring Radio Flux Scientists make measurements. In this lesson, you will continue to analyze images taken by the Green Bank Earth Station. You will continue to use the Sky Image Processor software. The result of your analysis will be intensity measurements taken on a group of different radio sources.
The set of images (left) shows the region of the galaxy containing the binary X-ray star Cygnus X-3. The radio radio flare of Cygnus X-3 is seen in the image labeled GP 8.4. Cygnus X-3 is the radio source at the center if the image. During the GPA survey (GPA 8.4) the X-ray star was quiet and is not seen. detected. The ROSAT X-ray satellite shows in this region, ONLY Cygnus X-3 is bright. The optical image (CYGNUS X-3) no hint of the exciting events going on inside the dark cloud.

The planetary nebula NGC 7027 Lesson 4: Measuring Distance In the fourth lesson, you will continue to analyze images taken by the Green Bank Earth Station. In lesson 4, the emphasis is on using image analysis software to compute the angular distance to an astronomical object and from that information, to calculate the distance to the object. A new analysis tool will be introduced in this lesson. You will link to the Aladin website. There is minimal mathematics required to perform this exercise.

A graph of intensity versus wavelength Lesson 5: Measuring Temperature In the fifth lesson, you will continue to analyze images taken by the Green Bank Earth Station. In lesson 5, the emphasis is on using image analysis software to compute the temperature of an astronomical object as measured by a radio telescope. Analyses and results from lesson 4 will be used to complete lesson 5. The algebraic equations required to perform this exercise are included in lesson 5.

Lesson 6: Observation at Different Wavelengths In the sixth lesson, you will observe the same object(s) at five different wavelengths in the electromagnetic spectrum. This lesson uses the NASA website SkyView.
Astronomers often observe the same object at different wavelengths in order to gather information about the object. According to the laws of physics, objects radiate at all wavelengths but the intensity of the radiation varies according to the objects temperature. Some objects are so faint at certain wavelengths that they appear to be invisible to the best earth-based telescopes.

Green Bank Earth Station Lesson 7: The Radio Telescope In this lesson, you will be introduced to the radio telescope as another tool used by astronomers. Radio telescopes are designed to collect radio signals emitted by objects in space. They use large antennas, accurate pointing programs, and sophisticated analyses tools to observe and map the objects in the Universe. There is no mathematical analysis necessary to complete this lesson.

Lesson 8: Mapping Objects with a Radio Telescope Lesson eight is an explanation of how a radio telescope makes a map of a region of the sky. The example used in this lesson is taken from observations of a supernova that occured in the year 1181 AD. This object continues to be visible as a reasonably bright radio source. There is no mathematical analysis necessary to complete this lesson

Lesson 9: Calibrating a Radio Telescope Radio telescope data must be calibrated against a known standard just like any other scientific measurement. This lesson presents the background necessary to understand an important task performed by astronomers. The calibration procedure allows an astronomer at one observatory to compare the results of his or her data against that same set of data taken by other astronomers at other observatories. As in the previous lessons, actual data obtained from an observation of the supernova remnant SNR1181 is used. There is no mathematical analysis necessary to complete this lesson

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Galactic Plane Science
2000-08-04

rwelsh@nrao.edu, glangsto@nrao.edu

	Lesson 1: The Discovery of the Milky Way The Milky Way Galaxy is a vast collection of over 100 billion stars. Our Sun is placed about two-thirds away from the center. It has taken almost four hundred years to understand our location in the Universe. In this lesson, you'll learn about advances in or understanding of the galaxy through history. There is no mathematics in this lesson, but plenty of links to other sites, which give more detailed information. The lesson ends with questions to be answered based on your understanding of each astronomer's contribution to our understanding of the Milky Way.
	Lesson 2: Introduction to Image Processing In the second lesson, you will analyze images taken by the Green Bank Earth Station. You will learn to use the image processing software program Sky Image Processor (SIP). The result of your analysis will be radio brightness measurements taken on a group of different radio sources. There is minimal mathematics required to perform this exercise.
	Lesson 3: Measuring Radio Flux Scientists make measurements. In this lesson, you will continue to analyze images taken by the Green Bank Earth Station. You will continue to use the Sky Image Processor software. The result of your analysis will be intensity measurements taken on a group of different radio sources. The set of images (left) shows the region of the galaxy containing the binary X-ray star Cygnus X-3. The radio radio flare of Cygnus X-3 is seen in the image labeled GP 8.4. Cygnus X-3 is the radio source at the center if the image. During the GPA survey (GPA 8.4) the X-ray star was quiet and is not seen. detected. The ROSAT X-ray satellite shows in this region, ONLY Cygnus X-3 is bright. The optical image (CYGNUS X-3) no hint of the exciting events going on inside the dark cloud.
	Lesson 4: Measuring Distance In the fourth lesson, you will continue to analyze images taken by the Green Bank Earth Station. In lesson 4, the emphasis is on using image analysis software to compute the angular distance to an astronomical object and from that information, to calculate the distance to the object. A new analysis tool will be introduced in this lesson. You will link to the Aladin website. There is minimal mathematics required to perform this exercise.
	Lesson 5: Measuring Temperature In the fifth lesson, you will continue to analyze images taken by the Green Bank Earth Station. In lesson 5, the emphasis is on using image analysis software to compute the temperature of an astronomical object as measured by a radio telescope. Analyses and results from lesson 4 will be used to complete lesson 5. The algebraic equations required to perform this exercise are included in lesson 5.
	Lesson 6: Observation at Different Wavelengths In the sixth lesson, you will observe the same object(s) at five different wavelengths in the electromagnetic spectrum. This lesson uses the NASA website SkyView. Astronomers often observe the same object at different wavelengths in order to gather information about the object. According to the laws of physics, objects radiate at all wavelengths but the intensity of the radiation varies according to the objects temperature. Some objects are so faint at certain wavelengths that they appear to be invisible to the best earth-based telescopes.
	Lesson 7: The Radio Telescope In this lesson, you will be introduced to the radio telescope as another tool used by astronomers. Radio telescopes are designed to collect radio signals emitted by objects in space. They use large antennas, accurate pointing programs, and sophisticated analyses tools to observe and map the objects in the Universe. There is no mathematical analysis necessary to complete this lesson.
	Lesson 8: Mapping Objects with a Radio Telescope Lesson eight is an explanation of how a radio telescope makes a map of a region of the sky. The example used in this lesson is taken from observations of a supernova that occured in the year 1181 AD. This object continues to be visible as a reasonably bright radio source. There is no mathematical analysis necessary to complete this lesson
	Lesson 9: Calibrating a Radio Telescope Radio telescope data must be calibrated against a known standard just like any other scientific measurement. This lesson presents the background necessary to understand an important task performed by astronomers. The calibration procedure allows an astronomer at one observatory to compare the results of his or her data against that same set of data taken by other astronomers at other observatories. As in the previous lessons, actual data obtained from an observation of the supernova remnant SNR1181 is used. There is no mathematical analysis necessary to complete this lesson