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Category Archives: 03. Light and telescopes: extending our senses

Astronomers from the International Centre for Radio Astronomy Research (ICRAR), in Perth in Western Australia, have produced what they call the GLEAMoscope to enable you to view the Milky Way over many different wavelengths, from gamma-ray to radio. (The name ‘GLEAM’ is derived from GaLactic and Extragalactic All-Sky Murchison Widefield Array.)


Credit: Natasha Hurley-Walker/GLEAM team


The plane of the Milky Way is shown as the horizontal across the middle. The north pole of the Galaxy is towards the top. Go to the GLEAMoscope website and use the sliding bar at the top left of the to change the wavelengths shown. (Note the image above is just a still and is not interactive.)  Different wavelengths reveal different features, from the dull red glow of hydrogen gas permeating through space, to the stars and dust clouds of our visible galaxy, and superhot gas generating x-rays.

Link: GLEAMoscope.

The Laser Interferometer Gravitational Wave Observatory (LIGO) was a topic of NPR’s Morning Edition, August 17, 2016.


Credit: Caltech/MIT/LIGO Lab

Read a full transcript or listen to the broadcast here (5 min 30s).

Here is a consolidated list of errors from the text’s first printing. Many of these have already been posted here as separate chapter updates. (Our publisher will make the necessary corrections to the printed book at the earliest opportunity.):

p. 25, Figure It Out 2.3: The last paragraph (about Fraunhofer) shouldn’t be there. Instead, it should be at the end of the caption of Figure 2-4 on p. 26.

p. 64, Q34: 1 Angstrom should be listed as 1010 m, not 108 m.

p. 64, Q41: Ditto

p. 78: There is an error in the equation relating the apparent magnitude and brightness of stars in Figure It Out 4.1.  In this equation, 2.512 should be raised to a power equal to (mB−mA).

p. 92, Q1: We could more clearly say “On the top picture” instead of just “On the picture” – since there are now two pictures on the opening page of the chapter (and the stars are somewhat too dense for individual clarity in the bottom picture).

p. 190: First sentence of Section 7.4d: “a little larger” should be “a little smaller” for the relative sizes of Triton and the Moon.

p. 309, Q53, there is a printing error when going from the bottom of column 1 to the top of column 2. At the top of column 2, the “(e)” should be boldface, there should be a period after “1/16”, and the remainder of the text should be deleted.

p. 363, column 1, second line from the bottom: When referring to the event horizon: “1/3” should be “2/3”, i.e. the sentence should read “Its radius is exactly 2/3 times that of the photon sphere…”

p. 391, column 2, second line from the bottom: for Spitzer, “Section 3.8c, Figure 3-32a).” should say simply “Section 3.8c).”

p. 392, column 1, line 5: At the end, add “(See Section 3.8c, Figure 3-32a.)”

Appendix 3C, column 3 header: “105 km” should be “106 km”

From a NuSTAR mission press release:

A mission designed to set its eyes on black holes and other objects far from our solar system turned its gaze back closer to home, capturing images of the Sun. In December 2014, NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, took its first picture of the Sun, producing the most sensitive solar portrait ever taken in high-energy x-rays.


Credit: NASA/JPL-Caltech

While the sun is too bright for other telescopes such as NASA’s Chandra X-ray Observatory, NuSTAR can safely look at it without the risk of damaging its detectors. The Sun is not as bright in the higher-energy x-rays detected by NuSTAR, a factor that depends on the temperature of the Sun’s atmosphere.

This first solar image from NuSTAR gives insight into questions about the remarkably high temperatures that are found above sunspots. Future images will provide even better data as the Sun winds down in its solar cycle, with the potential to capture hypothesized nanoflares – smaller versions of the Sun’s giant flares that erupt with charged particles and high-energy radiation.

Links: NuSTAR press release, full-view image of the Sun’s disk.

From a press release of the Max Planck Institute for Radio Astronomy, April 21, 2015:

Joint observations by the Atacama Pathfinder Experiment (APEX) telescope in Chile and Antarctica’s largest astronomical telescope come closer to making detailed images of the supermassive black hole in the centre of the Milky Way, up to its very edge, the “event horizon”. These successful observations were conducted within the framework of the Event Horizon Telescope – a virtual telescope as big as planet Earth.

Event Horizon Telescope

Credit: © Dan Marrone/University of Arizona

The South Pole Telescope (SPT) and APEX joined together in a ‘Very Long Baseline Interferometry’ experiment for the first time in January 2015. The two telescopes together observed two sources — the black hole at the centre of the Milky Way galaxy, Sagittarius A*, and the black hole at the centre of the nearby galaxy Centaurus A — and combined their signals to synthesize a telescope 7,000 kilometres across. With this success, the SPT joins the Event Horizon Telescope array, which connects APEX, the Large Millimeter Telescope in Mexico, the Submillimeter Telescope in Arizona, the Combined Array for Research in Millimeter-wave Astronomy in California, the Submillimeter Array and James Clerk Maxwell Telescope in Hawaii, and the Institute for Radio Astronomy Millimetrique (IRAM) telescopes in Spain and France.

Even though the Milky Way’s black hole is 4 million times more massive than the Sun, it is tiny to the eyes of astronomers. Smaller than Mercury’s orbit around the Sun, yet almost 26,000 light years away, studying its event horizon in detail is equivalent to standing in New York and reading the date on a cent in Germany.

With its unprecedented resolution, more than 1,000 times better than the Hubble Telescope, the EHT will see swirling gas on its final plunge over the event horizon, never to regain contact with the rest of the universe. If the theory of general relativity is correct, the black hole itself will be invisible because not even light can escape its immense gravity. However, it might still be seen as a silhouette against the background.

Links: MPIfR press release; EHT home.

In Questions 34 and 41, on p. 64, the angstrom unit, Å, is given incorrectly.

1 angstrom, Å = 10–10 m  (so, 1 Å = 10–8 cm).

From an article by Kelly Beatty in Sky & Telescope, November 30, 2014:

A year ago, the situation looked bleak for historic Lick Observatory, the venerable 125-year-old mountaintop facility that overlooks California’s Silicon Valley. Faced with huge commitments to support its investment in Hawaii’s Keck Telescopes and to help fund the billion-dollar Thirty Meter Telescope, officials at the University of California (which owns and operates Lick) decided there just wasn’t enough money to go around. So they decreed that Lick should be divested from the university and find its own funding, with a “glide path” toward self-sufficiency to begin within two years and be completed by 2018.

Credit: Debra and Peter Ceravolo

Credit: Debra and Peter Ceravolo

Needless to say, the September 2013 announcement rocked the astronomical community in a way that few of the area’s earthquakes ever could. Although “closure” was never actually stipulated, it loomed as the most likely outcome for a venerable institution that held a premier role in U.S. astronomy a century ago. Prominent members of the astronomical community cried out in protest. Cosmologist (and author of The Cosmos) Alex Filippenko (UC Berkeley) led a “Save Lick Observatory” campaign. California congressmen petitioned the university’s president to reconsider the decision. The area’s amateur astronomers mobilized for a fight. Apparently, all that high-profile resistance – coupled with some belt-tightening – has spared Lick from being cast adrift.

While the observatory’s short-term prospects are now relatively secure, proponents are taking steps to ensure its long-term survival. A Lick Observatory Council, involving Filippenko, other scientists, and private citizens, has started private fundraising efforts and to expand the observatory’s outreach and education programs.

Links: the full article in Sky & Telescope; Lick Observatory public information.

Read an up-to-date survey of various new telescopes and systems, by Dennis Overbye of The New York Times (July 21, 2014).

Overbye discusses the funding, construction, and schedule for the E-ELT, the Giant Magellan Telescope, and the Thirty-Meter Telescope, as well as the Large Synoptic Survey Telescope. For space telescopes, he discusses the new Hubble-class satellites given to NASA by the National Reconnaissance Office, to be used in Wfirst-AFTA (he quotes David Spergel of Princeton as saying that “The good thing about Wfirst-AFTA is that there is no way that we will keep that name.” He winds up by discussing the case of the James Webb Space Telescope, due for launch in 2018, now on its revised budget and schedule, following its role as “the telescope that ate astronomy.”

Credit: Ball Aerospace

Credit: Ball Aerospace

Links: the NY Times article by Dennis Overbye.

The Sloan Digital Sky Survey (SDSS) is one of the most ambitious and influential surveys in the history of astronomy. Over eight years of operations it has obtained deep, multi-color images covering more than a quarter of the sky and created 3-dimensional maps containing more than 930,000 galaxies and more than 120,000 quasars.

Credit: Sloan Digital Sky Survey

The education team at SDSS have prepared a variety of astronomical resources, interactive tools, and science projects, for teachers and educators to use. They aim to show us the beauty of the Universe, and share with us their excitement as they build the largest map in the history of the world!

SkyServer‘s tools allow you to access all publicly available data from the Sloan Digital Sky Survey. It offers access to many different types of data, but most users will usually focus on four types: images, spectra, photometric data, and spectroscopic data. See their ‘Getting Started‘ page for more details.

Their projects pages come in both Basic (suitable for high-school and Astronomy 101-level students) and Advanced (for students with a deeper understanding of astronomy) levels.  There are also ideas for extended independent research projects.

Instructor guides are also available.

One of the most famous objects in the sky, the Cassiopeia A supernova remnant (see Figure 13-18c) – Cas A, for short – has been rendered for display like never before, thanks to NASA’s Chandra X-ray Observatory and a new project from the Smithsonian Institution. A new three-dimensional viewer allows users to interact with many one-of-a-kind objects from the Smithsonian as part of a large-scale effort to digitize many of the Institutions objects and artifacts.

Scientists have combined data from Chandra, NASA’s Spitzer Space Telescope, and ground-based facilities to construct a unique 3D model of the 300-year old remains of a stellar explosion that blew a massive star apart, sending the stellar debris rushing into space at millions of miles per hour. The collaboration with this new Smithsonian 3D project allows the astronomical data collected on Cas A to be featured and highlighted in an open-access program.



To coincide with Cas A being featured in this new 3D effort, a specially-processed version of Chandra’s data of this supernova remnant has been released. This new image shows with better clarity the appearance of Cas A in different energy bands, which will aid astronomers in their efforts to reconstruct details of the supernova process such as the size of the star, its chemical makeup, and the explosion mechanism. The color scheme used in this image is the following: low-energy X-rays are red, medium-energy ones are green, and the highest-energy X-rays detected by Chandra are colored blue.

Cas A is the only astronomical object to be featured in the new Smithsonian 3D project. This and other objects in the collection – which include the Wright brothers plane, a 1600-year-old stone Buddha, a gunboat from the Revolutionary War, and fossil whales from Chile – were showcased in the Smithsonian X 3D event on November 13th and 14th at the Smithsonian in Washington, DC.

Links: Smithsonian X 3D beta tour; Chandra X-ray Center press release; NASA press release; YouTube movie of a fly-through.