In the Sky this Week – September 5, 2017
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Mercury and Mars make a reappearance very low in the eastern morning sky - so low in fact, you may have trouble seeing them if you have low shrubs; atmospheric turbulence and light pollution may also make them difficult to spot.

Eastern sky before sunrise, Sept. 5, 2017

Eastern sky before sunrise, Sept. 5, 2017, 6:00 AM. Credit: Stellarium / Bob Trembley.

Over the week, Mars will not get any higher in the sky, but Mercury will get visibly higher each morning. Mercury will be very close to the star Regulus in Leo on Sept. 10th. Catch Mercury while you can - by next week, Mercury will start getting lower in the sky, and will vanish entirely by late September.

Conjunction of Mercury, Mars, and Regulus - Sept. 10, 2017

Conjunction of Mercury, Mars, and Regulus in the eastern sky before sunrise, Sept. 10, 2017, 6:00 AM. Credit: Stellarium / Bob Trembley.

The full Moon rises in the east with the sunset on Sept. 5th; Saturn remains high in the southern sky, after sunset.

Southern sky after sunset, Sept. 5, 2017

Southern sky after sunset, Sept. 5, 2017, 9:00 PM. Credit: Stellarium / Bob Trembley.

Polaris, the North Star, is visible above the northern horizon before dawn. Two of Polaris' three stars can be made out in a modest sized telescope; Polaris A, the primary component of the trinary is a Cepheid variable star, ranging in magnitude from 1.86 - 2.13, with a period of roughly 4 days. Have a look at Polaris - compare its brightness with stars around it; now, do the same the next night - see if you can spot a difference.

Polaris above the northern horizon, Sept. 5, 2017

Polaris above the northern horizon, Sept. 5, 2017. Credit: Stellarium / Bob Trembley.

This video shows the stars of the Polaris trinary and an approximation of their orbits:

There are multiple rather large sunspots on the Sun this week - grab those solar glasses and go back out and see if you can spot them - they're HUGE!

The Sun - Sept. 4, 2017

The Sun - Sept. 4, 2017 - Helioseismic and Magnetic Imager (HMI). Image courtesy of NASA/SDO and the AIA, EVE, and HMI science teams. / Bob Trembley.

Sunspot group AR2673 showed dramatic growth last weekend:

Expanding Sunspot

On Saturday, Sept. 2nd, AR2673 was a typical small sunspot. On Sunday, Sept. 3rd, it grew massively. Image courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.

The Sky Overhead:

The Sky Overhead: Sept. 5, 2017 10:00 PM

The Sky Overhead: Sept. 5, 2017 10:00 PM. Credit: Stellarium / Bob Trembley.

The Solar System:

The Solar System - Sept. 5, 2017

The Solar System - Sept. 5, 2017. Credit: NASA Eyes on the Solar System / Bob Trembley.

The Solar System with Asteroids and Comets:

Solar System with small bodies - Sept. 5, 2017

Solar System with small bodies - Sept. 5, 2017. Credit: NASA Eyes on the Solar System / Bob Trembley.

Looking at the inner solar system from a vantage point behind the Earth:

The Solar System, seen from near Earth - Sept. 5, 2017

The Solar System, seen from near Earth - Sept. 5, 2017. Credit: NASA Eyes on the Solar System / Bob Trembley.

Apps used for this post:

Stellarium: a free open source planetarium app for PC/MAC/Linux.
Universe Sandbox ²: a physics-based 3D space simulator.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission app - free for the PC /MAC.
Space Engine: a realistic virtual Universe you can explore on your computer - free for the PC.


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