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June Night Sky

June night sky

Charlie Christmann

Transits and Eclipses:

An eclipse is the obscuration of the light of the moon by the intervention of the earth between it and the sun (lunar eclipse) or the obscuration of the light of the sun by the intervention of the moon between it and a point on the earth (solar eclipse).

An astronomical transit is defined as the movement of a smaller object across and in front of a larger object, or the passage of a smaller object’s shadow across the face of a larger object.

This month we have both a partial lunar eclipse and a rare transit.


Astronomers, looking for planets outside our solar system are faced with a daunting task. The glare of the star all but wipes out the light reflected by the planet. Because of this glare, only a handful of exoplanets have been directly observed.

Early detections were made using the “wobble method” which uses the Doppler Effect to see the small tug of a planet making the star wobble as the planet whips around in its orbit. This method is best at detecting large planets very close to the star.

Astronomers knew that looking for planets transiting a star outside our solar system was possible, if space-based detectors could see the change of just a few tenths of a percent in the light coming from a distant star. The Kepler spacecraft was designed just for that purpose and was launched in 2009.

Kepler stares at a small patch of sky in the constellation Cygnus, the Swan, looking for the miniscule dimming of a star as a planet transits. Of the more than 145,000 stars it watches, Kepler has found 2,321 likely planets orbiting 1,790 stars since its launch; 61 planets have been confirmed so far. Originally scheduled to end in November of this year, Kepler’s mission has been extended for two more years so that it can attempt to find earth-like planets in orbits that could possibly sustain life.

Inner Planet Transits:

From Earth, only two of our neighboring planets can transit the sun: Mercury and Venus. Transits are governed by the alignment of Earth, the sun, and the other planets, the time it takes for the inner planet to catch up to the Earth in its orbit, and the angle between the orbits.

Mercury’s orbit is inclined seven degrees to Earth’s. The two orbits cross with the sun behind Mercury at two points. Those occur in May and November. Inferior conjunctions happen when, looking from above the orbits of the planets, an inner planet lines up between the outer planet and the sun.  If Mercury passes through inferior conjunction in May or November, a transit will occur. 

The last transit of Mercury occurred in 2006, the next ones will happen on May 9, 2016 and November 11, 2019. On average, there are thirteen transits of Mercury each century.

A Very Rare Transit:

Transits of Venus are much rarer. The angle between Earth’s orbit and Venus’s orbit is only 3.4 degrees and usually appears to pass under or over the Sun in the sky at inferior conjunction. Again, the orbits align only at two points to allow a transit: June and December. The rarity comes from the fact that the two planets reach inferior conjunction about every 1.6 years. This “about” causes some interesting timing. Venus transits occur in sets of two spaced 105.5 or 121.5 years apart. The time between the pared transits is eight years. The last transit of Venus—and the first of this set—happened in June of 2004. June 2012 is eight years later, and this will be your only chance to see the event from New Mexico in your life-time, although the sun here will set during the event. The next transit of Venus is scheduled for 2117.

The 2012 transit starts at 4:05 p.m. and ends at 10:48 p.m. Unfortunately, sundown is 8:17 p.m., so we only get to see the first two-thirds. To best see the event, binoculars or a small telescope is needed. Make sure you have proper solar filters if you choose to use magnification, the sun WILL blind you.

Viewing parties are taking place in Albuquerque. See for specifics. Or if you want to stay home, several organizations are planning webcasts. See for more information.

Lunar Eclipse:

There is a partial Lunar Eclipse on the fourth. The umbra just touches the moon starting about 3:59 a.m. Maximum coverage will be at 5:03 a.m. Again, the moon set will cause us to miss the end of the event. The moon is full at 5:12 a.m. on the fourth and new at 9:02 a.m. on the nineteenth.

The Planets:

• Look for Mercury late in the month low in the west after sunset. On the twentieth, find Mercury just below Castor, and Pollux in Gemini an hour after sunset in the WNW.

• Venus will be in the glare of the sun as it transits on June fifth. It will be visible again starting mid-month in the morning sky. On the eighteenth, about fifteen minutes before sunrise, the moon will be six degrees to the lower left of Venus.

• Mars will be in the WSW after sunset.

• Jupiter rises around 5:00 a.m. early in June and about 4:00 a.m. late in the month. On the seventeenth, Jupiter will be in the ENE one degree to the right of the moon. Venus will follow about thirty minutes later seven degrees to the lower left of the moon.

• Saturn is in the SW after sunset. On the 27th, Saturn will be eight degrees above the moon, Mars will be 24 degrees to the right of the moon, and Spica will be five degrees to the upper left of the moon.

• Summer begins at 5:09 p.m. on the twentieth.

Watch the transit of Venus with the Rio Rancho Astronomical Society in Bernalillo

On June 5, the RRAS will have solar telescopes set up at Coronado State Monument to observe the transit of Venus, where Venus will cross the face of the Sun. This will be the last transit of Venus seen from Earth until 2117. Telescopes will be set up in the Coronado parking lot next to the entrance to the museum starting at 2:00 p.m. The transit will start at 4:05 p.m. and continue until past sunset. Special eclipses glass will be available for sale to allow safe viewing. For more information, visit our website at or call 220-5492.

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