Mercury at Western Elongation

19jan-mercury-east-elongation
   On Tuesday September 12th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation at 17.9o. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows. Even though it sounds confusing at western elongation for either Mercury or Venus the inner planet will be to the right of the Sun as we view them, meaning that at western elongation an inner planet rises in the east before the Sun rises. And at eastern elongation with the inner planet on the left side of the Sun the inner planet follows the Sun across the sky setting after the Sun sets.
orbital-positions
   From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!

   Mercury is visible in the morning skies before sunrise along with Mars, Venus, and the star Regulus as this graphic shows.

   
   
   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.

Venus at Western Elongation

inner-planets-positions   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.

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Mercury at Western Elongation

28sep-mercury-west-elongation
   Wednesday September 28th the innermost planet Mercury reaches its greatest western elongation. At this elongation Mercury is to the right or the west side of the Sun as we see it from Earth. From western elongation Mercury moves eastward toward the Sun and superior conjunction next month on October 27th.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.

Mercury at West Elongation

5 June-mercury-at-west-elongation
   On Sunday June 5th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows. Even though it sounds confusing at western elongation for either Mercury or Venus the inner planet will be to the right of the Sun as we view them, meaning that at western elongation an inner planet rises in the east before the Sun rises. And at eastern elongation with the inner planet on the left side of the Sun the inner planet follows the Sun across the sky setting after the Sun sets.
orbital-positions
   From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!


   Mercury is visible in the morning skies before sunrise as this graphic shows.
   
   
   
   
   

Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Venus at Western Elongation

inner-planets-positions   Monday October 26th 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 46.4o 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.

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Mercury at Western Elongation

orbital-positions   On Friday October 16th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows.
   From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!
16oct   Both Mercury and Venus are visible in the morning skies before sunrise as this graphic shows. The orbits of both inner planets are shown where they will be on the 16th. Mercury is at western elongation while Venus will be at its western elongation 10 days later on the 26th.

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Venus at its Brightest

   Have you noticed that bright shining ‘star’ in the morning skies? At this time of the year you could be thinking I am referring to Sirius, the brightest night time star. While Sirius, no kidding, has an apparent magnitude of -1.4 it is out shined by the inner planet Venus now rising about 2-3 hours before sunrise local time. Venus currently has an apparent magnitude of -4.54 and coincidentally Venus is at its greatest brilliance.

Venus monthly: January-December 2015

Venus monthly: January-December 2015

   This is not the first time that Venus has been at its greatest brightness as this point in Venus’s orbit occurs as a function of the planet’s orbital position relative to the Earth and the Sun. Venus increases in its apparent size as it moves from superior conjunction, behind the Sun through eastern elongation to inferior conjunction. During this time Venus goes through phase changes starting with a waning gibbous phase following superior conjunction to a new phase at inferior conjunction. At this point Venus is at its greatest apparent size however we will not see Venus until it moves away from inferior conjunction. As Venus moves toward western elongation and then to superior conjunction its apparent size decreases while it goes from a large crescent shape to a smaller waxing gibbous phase.
   Venus was at inferior conjunction this past August 15th so it was last at its greatest brightest on July 12th when it was a large but thin waning crescent shape. Now Venus is moving past inferior conjunction and is at a orbital position similar to the one it had in July making Venus appear at its greatest brightness.

   
   
   
   

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.