Mars at Opposition

Mars will be at opposition on May 22nd, 2016.

From a previous post, we know that opposition occurs when the planet and the Sun are 180° away from each other in the sky. What this means is that when the Sun is setting, the planet will be rising. In the next couple of days, if you look to the east at sunset, Mars will be rising above the horizon. A great time to view Mars would be at midnight when it is near the apex of its path across the sky. Mars will be in Scorpius (the constellation opposite the Sun's location in Taurus) as seen here.

Because Mars is at opposition, it is the closest to us, but is still about 0.4 AU (60 million kilometers or 37.2 million miles) away from us.

TRAPPIST-1 Planets

TRAPPIST-1 is an M8 dwarf star which is one of the coldest stars on the Hertzsprung-Russell Diagram. It has a surface temperature of about 2550 K (the Sun, by comparison has a surface temperature of 5800 K) and a mass of approximately 0.08 Solar masses.


Recently, astronomers led by Michael Gillon of the University of Liege announced that they discovered three planets orbiting TRAPPIST-1 using the transit method. The two closest are tidally locked to their parent star, much like the Moon is tidally locked to Earth. However, the third planet lies just at the outer edge or beyond the habitable zone of the star.


Theoretically, this planet could harbor life, but in all likelihood, it would nothing like Earth life. By being in the habitable zone, this means that water would be in liquid form, which astronomers believe would be necessary for life to exist.

Transit of Mercury

On May 9, 2016, the planet Mercury will transit across the face of the Sun and for most of the Earth, the transit will be visible (or at least portions of it).


The transit begins at 11:12 UTC (Coordinated Universal Time measured at Greenwich, England) and ends at 18:42 UTC. To determine your time offset from UTC, Wikipedia has a good summary. For example, in Pittsburgh (where I live), we are currently only four hours behind UTC due to daylight savings time. So in Pittsburgh, the transit begins at 7:12 AM and ends at 2:42 PM.


To see the transit, you should not look directly at the Sun.. There are a couple of ways to look at it, however.

1. Have a Sun filter for a telescope, binoculars, or camera.
2. Watch it online at NASA.gov.

If you recall (or even if you don't), a transit is similar to an eclipse and an occultation. A transit is when a planet crosses in front of its parent star as seen from Earth. On Earth, only Mercury and Venus can transit the Sun. Unfortunately, many of us alive today will never witness another transit of Venus, as the last two took place in June of 2004 and June of 2012. The next transit of Venus will not take place until December of 2117. Mercury has a much shorter period of transits, approximately every three years, so if you miss this transit, you will only have to wait until November 2019.