Counting stars with Gaia

This image, based on housekeeping data from ESA’s Gaia satellite, portrays the outline of our Galaxy, the Milky Way, and of its neighbouring Magellanic Clouds. It was obtained by plotting the total number of stars crossing Gaia’s focal plane per second - this is a measure of the density of stars in the region that is being scanned.

An annotated version of the image is available here.

Credit: ESA/Gaia-CC BY-SA 3.0 IGO

Johann Gabriel Doppelmayer - Tabula Selenographica (The first comparative chart of the Moon from which the names of many Lunar features have been derived), 1707.

Essentially a comparative chart, Doppelmayer constructed this map to illustrate the Lunar mapping of Johannes Hevelius (left) and Giovanni Battista Riccioli (right). The left hand Lunar map, composed by Hevelius, is a considered a foundational map in the Science of Selenography – or Lunar cartography.

This map first appeared in Hevelius’ 1647 work Selenographia which laid the groundwork for most subsequent Lunar cartographic studies. Here the Moon is presented as it can never be seen from Earth, at a greater than 360 degrees and with all visible features given equal weight. In this map Hevelius also establishes the convention of mapping the Lunar surface as if illuminated from a single source – in this case morning light. The naming conventions he set forth, which associate Lunar features with terrestrial locations such as ‘Asia Minor,’ 'Persia,’ 'Sicilia’, etc, were popular until the middle of the 18th century when Riccioli’s nomenclature took precedence.

The Riccioli map, on the right, is more properly known as the Riccioli-Grimaldi map. This was a significant Lunar chart and offered an entirely new nomenclature which, for the most part, is still in use today. Curiously, though Riccioli, as a devout Jesuit, composed several treatises denouncing Copernican theory, he chose to name one of the Moon’s most notable features after the astronomer – perhaps suggesting that he was a secret Copernicus sympathizer? Other well-known Lunar features named by Riccioli include the Sea of Tranquility where Apollo 11 landed and where Neil Armstrong became the first human to set foot on the Moon’s surface. The upper left and right hand quadrants feature decorative allegorical cartouche work that include images of Angelic children looking through a telescope and a representation of the Ancient Greek Moon goddess Selene. Additional mini-maps show the Moon in various phases of its monthly cycle. Below the map proper extensive Latin text discusses Selenography.

NASA Astronomy Picture of the Day 2015 August 2 

Apollo 17 at Shorty Crater 

On the Moon, it is easy to remember where you parked. In December of 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours on the Moon in the Taurus-Littrow valley, while colleague Ronald Evans orbited overhead. This sharp image was taken by Cernan as he and Schmitt roamed the valley floor. The image shows Schmitt on the left with the lunar rover at the edge of Shorty Crater, near the spot where geologist Schmitt discovered orange lunar soil. The Apollo 17 crew returned with 110 kilograms of rock and soil samples, more than was returned from any of the other lunar landing sites. Now forty three years later, Cernan and Schmitt are still the last to walk on the Moon.


Venus: Crash Course Astronomy #14 By CrashCourse

Venus is a gorgeous naked-eye planet, hanging like a diamond in the twilight – but it’s beauty is best looked at from afar. Even though Mercury is closer to the sun, Venus is the hottest planet in the solar system, due to a runaway greenhouse effect, and has the most volcanic activity in the solar system. Its north and south poles were flipped, causing it to rotate backwards and making for very strange days on this beautiful but inhospitable world.

Table of Contents

Venus’s Size and Atmosphere 3:09
Hottest Planet in the Solar System 4:04
Slow Clockwise Rotation 6:02
Tremendous Volcanic Activity 8:31