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Category Archives: 11. Stars: distant suns

From an ESA press release, September 14, 2016 :

The first catalogue of more than a billion stars from ESA’s Gaia satellite was published on September 14, 2016 – the largest all-sky survey of celestial objects to date.

On its way to assembling the most detailed 3D map ever made of our Milky Way galaxy, Gaia has pinned down the precise position on the sky and the brightness of 1.142 billion stars. As a taster of the richer catalogue to come in the near future, this data release also features the distances and the motions across the sky for more than two million stars.


Credit: ESA/Gaia/DPAC

The map projection above shows an all-sky view of stars in the Milky Way and our neighboring galaxies, based on the first year or so of Gaia’s observations. It shows the density of stars observed by Gaia in each portion of the sky. Brighter regions indicate denser concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed. Darker regions across the Galactic Plane correspond to dense clouds of interstellar gas and dust that absorb starlight along the line of sight. Many globular and open clusters – groupings of stars held together by their mutual gravity – are also sprinkled across the image.

Note that the faint curved features and dark stripes are not of astronomical origin but rather reflect Gaia’s scanning procedure. As this map is based on observations performed during the mission’s first year, the survey is not yet uniform across the sky. These artefacts will gradually disappear as more data are gathered during the five-year mission.

Links: ESA press release, Gaia sky map.

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”

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, answer choice “(e)” should be in bold type and there should be a period after “1/16.”  The remainder of the text should be deleted because it repeats the previous sentence.

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.

The European Space Agency’s billion-star surveyor, Gaia was launched into space on Thursday December 19, 2013, where it will embark on its mission to create a highly accurate 3D map of our galaxy. (See pp. 285, 290.)


Credit: ESA

By repeatedly observing a billion stars, with its billion-pixel video camera, the Gaia mission will allow astronomers to determine the origin and evolution of our galaxy whilst also testing gravity, mapping our inner Solar System, and uncovering tens of thousands of previously unseen objects, including asteroids in our Solar System, planets around nearby stars, and supernovae in other galaxies.

Gaia will map the stars from an orbit around the Sun, near a location some 1.5 million km beyond Earth’s orbit known as the L2 Lagrangian point. The spacecraft will spin slowly, sweeping its two telescopes across the entire sky and focusing their light simultaneously onto a single digital camera, the largest ever flown in space. The ‘eye’ of Gaia’s camera has the most sensitive set of light detectors ever assembled for a space mission.

Once Gaia starts routine operations, in late Spring 2014, astronomers will have the challenge of dealing with a flood of data. Even after being compressed by software, the data produced by the five-year mission will fill over 30,000 CD-ROMs!

The first Gaia science is expected to be discoveries of new sources – supernovae, extreme variable stars, and blazars.

Links: University of Leicester press release; ESA launch campaign blog and press release; ESA lift-off movie.