Saturday June 3rd Venus reaches the point in its orbit called greatest western elongation. As this graphic shows the inner planet Venus, or Mercury, is more or less at a right angle (90o) from the Sun and Earth at western elongation. From the surface of the Earth, your backyard, for example, Venus is to the right, or western side of the Sun and is rising before the Sun.
At western elongation Venus, or for that matter Mercury the other inner planet, is as far out from the Sun as we see them and as a result Venus or Mercury will rise at the latest time in this orbit. On the day of the western elongation Venus will be 45.9o from the Sun. From western elongation forward Venus or Mercury will be moving eastward toward the Sun and each day rising closer and closer to the time of sunrise. As the planet moves eastward it is moving further away from the Earth toward superior conjunction on the opposite side of the Sun.
As the distance between the Earth and Venus, or Mercury, increases combined with the decreasing angle between the planet, the Earth, and the Sun, Venus or Mercury decreases in apparent size and also waxes through gibbous phase shapes but we never see it at a full phase since that is at superior conjunction.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.
Monday morning May 22nd the 25.6-day old waning crescent Moon will be within about 3o from the inner planet Venus. Both of which will fit nicely within the field of view of binoculars.
What is that really bright star over the eastern horizon in the hours before sunrise? That is the inner planet planet Venus, and on Sunday April 30th Venus will reach a point in its orbit around the Sun where it appears at its greatest illumination. Shining at an apparent magnitude of around -4.53 Venus is bright enough to drown out most of the stars in the constellation of Pisces the Fishes that surround Venus.
How Venus gets this bright is a result of its orbit around the Sun and its position relative to the light from the Sun and us on Earth. Venus is currently about as close to the Earth as it can come and because it is between us and the Sun Venus goes through phase changes like our Moon. Except we cannot see a full Venus because that is when Venus is at superior conjunction, on the opposite side of the Sun.
Venus was recently at inferior conjunction and is now moving along its orbit toward the west away from the Sun. From inferior conjunction, for a while, Venus will appear as a large crescent shape but as days pass it moves further away, grows smaller in apparent size, and increases, waxing, toward a small gibbous phase before it moves behind the Sun and superior conjunction.
Sunday morning April 23rd the thin 26-day old waning crescent Moon will rise to right, west, from the inner planet Venus. The two will be about 6o apart and will easily fit within the field of view of 7×50 binoculars.
Saturday March 25th the inner planet Venus reaches its orbital position known as inferior conjunction.
This is one of four points along an inner planet orbit. At inferior conjunction Venus is between the Earth and the Sun – sort of like our new Moon phase – but not necessarily directly in line. If that were so, inferior conjunction at the same time as Venus in direct line with the Earth and Sun (a node crossing at inferior conjunction) it would be a somewhat rare transit of the Sun by Venus. These happen as a pair of transits about one time each century with the last pair of Venus transits in June 2004 and June 2012. Here are some pictures of the June 2012 Venus Transit. Here is a link to the Vimeo web site to watch a video of the 2012 Venus Transit.
By the way the next pair of Venus Transits are December 2117, and December 2125.
Thursday evening March 2nd watch for the 4.5-day young waxing crescent Moon to be about 2o away from Dwarf Planet Ceres. Seeing Ceres with an apparent magnitude of around 8 may be difficult when the Moon is this close, especially using binoculars.
However with a telescope Ceres should resolve into a small disc shape as this simulated view with a 25mm eyepiece on a 6″ reflector shows. There are two 6th magnitude stars on either side of Ceres that could be used as reference points for Ceres location if you are following the Dwarf Planet as it moves along its orbit.