Viewing the Universe

Astronomers gather information about objects throughout the universe by detecting various kinds of energy given off by these objects.

We call the various types of energy electromagnetic radiation, or energy that can travel through space in the form of waves.

The electromagnetic spectrum includes radio waves, infrared radiation, visible light, ultraviolet radiation, x-rays and gamma rays.

Telescopes collect and focus different types of electromagnetic

radiation

Radio astronomy imageSeyfert galaxy NGC 4151

Infrared image of young planetary nebula known as BD+303639

Visible image of four galaxies, known as Hickson Compact Group 87 (HCG 87)

Ultraviolet image of the sun

ETACAR NEBULA USING X-RAY IMAGING

Pulsars in the Crab Nebula using Gamma Imaging

The Hubble Space Telescope is a reflecting telescope with a mirror. Because it is above our atmosphere, it can collect images with more detail.

The Hubble can also collect ultraviolet and infrared radiation.

There are two types of visible light telescopes

Refracting telescopes use a lens to focus light Reflecting telescopes use a mirror to focus

the light. Large modern telescopes are now all

reflecting telescopes.

When we pass visible light through a prism, it is spread out to make a continuous range of its different colors.

We call this ROY G. BIVRed, Orange, Yellow, Green, Blue, Indigo and Violet

Most large telescopes include a spectroscope to break visible light

from a stellar object into its spectrum.

By comparing the star’s spectrum with the spectrum of elements known on earth, we can infer which elements

are found in that star.

In the next week we will look at three types of spectra

Continuous spectrum - all of the colors of the visible spectrum

Emission spectrum - bright lines of color given off when the gaseous state of an element is excited

Absorption spectrum - spectrum with black lines or missing colors given off when light is passed through a chemical.

We will also learn about the apparent change in the wavelengths of light that occurs when an object is moving toward or away from the Earth

This is called the Doppler effect.

If a star is approaching the Earth, the light waves are pushed together. They appear shorter that they really are. Shorter wavelengths are characteristic of blue and violet light. The spectrum appears to be shifted slightly toward the blue end. We call this a blue shift.

If a star is moving away, the light waves expand, appearing longer than they really are. We call this a red shift.

The more a spectrum is shifted, the faster a star is moving.

The light from every distant galaxy shows a red shift.

Every galaxy in the universe seems to be moving away from the Earth. The universe is expanding. Galaxies at the edge are racing away. Galaxies closer to the center are moving out at slower speeds.