spectra

How Telescopes Work

Discipline: 
Education

This guide describes how telescopes work. Telescopes are the fundamental tool in observational astronomy, and understanding their capabilities and limitations is central to understanding what we can learn from them. You will find that the text contains many links. Some will take you to a glossary definition, while others are links to more information about a topic you may want to explore further. Please use this guide in the way that makes most sense to you. You may want to read the entire guide first, then go back and follow links that interest you, or you

Tags: 
spectra
optics
seeing
refracting
reflecting
CCD
spectrograph
field of view
angular resolution

Types of Stars

Discipline: 
Education

Astronomers have always been fascinated by the different sizes and colors of stars that they observed. In 1817 an German instrument maker named Joseph Fraunhofer attached a spectroscope to a telescope and pointed it at the stars. He found that different stars have different absorption lines in their spectra. At first astronomers did not understand why different stars would have different absoprtion lines. Nevertheless in the early 1900s, a team of astronomers at Harvard College Observatory started a project to examine the spectra of hundreds of thousands of stars.

Tags: 
stars
spectra
spectral class
temperature
Henry Draper
Annie Jump Cannon
Antonia Maury
Edward Pickering

The Mean Type Ia Supernova Spectrum Over the Past 9 Gigayears

We examine the possibility of evolution with redshift in the mean rest-frame ultraviolet (UV; <4500A) spectrum of Type Ia Supernovae (SNe Ia) sampling the redshift range 0<z<1.3. We find new evidence for a decrease with redshift in the strength of intermediate-mass element (IME) features, particularly Si II and to a lesser extent Ca II "H&K" and Mg II blends, indicating lower IME abundances in the higher redshift SNe. A larger fraction of luminous, wider light-curve width (higher "stretch") SNe Ia are expected at higher redshift than
Sullivan, M., Ellis, R. S., Howell, D. A., Riess, A., Nugent, P. E., & Gal-Yam, A. 2009, ApJL, accepted, astro-ph/0901.2476