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.

Mars Meets Saturn

Click on graphic to see it full size.

Click on graphic to see it full size.

   Monday evening the 25th of August Mars and Saturn will be at their closest to one another as they are separated by less than 1o. This occurs at 18 UT, 1 pm CDT. Both planets are moving eastward along their respective orbits with Mars (0.519o per day) being closer to the Sun moving faster than Saturn (0.0334o per day). For my time zone the closest approach will occur during the afternoon but by sunset the separation will not have increased by that much.

   Using binoculars, or just your eyes, compare the apparent magnitude of Mars (0.59), Saturn (0.59), and Zubenelgenubi (2.75). This is a good example of how distance is the key to apparent magnitude. For solar system objects, (planets, moons, asteroids, comets), how much sunlight is reflected is determined by the overall apparent size of the object’s disk. In the case of Saturn its ring system spans around 200,000 miles and with an apparent size like that Saturn is able to reflect enough sunlight so that despite its greater distance from the Sun Saturn, at varying times during its orbit around the Sun, may appear as bright or brighter than Mars.

   
   
   
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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.

She’s Back!

venus20-31jan-ani   Did you notice a bright star rising just ahead of the Sun this morning? If so you are looking at the planet Venus as it moves westward away from the Sun in the morning skies. Venus was recently at inferior conjunction, between the Earth and the Sun on 11 January. Over the next two months Venus will continue moving out away from the Sun rising earlier each morning as this animated graphic is showing. The graphic is set at 1-day intervals and runs from the 20th, today, through the 31st of January.

phases-ani20-31jan   Venus moving away from inferior conjunction will undergo phase changes similiar to our Moon. Inferior conjunction is sort of like a new Moon and so as Venus moves westward away from the Sun and increasing the angle between the two Venus will first appear as a relatively large and very thin crescent. Over time Venus’s apparent size will decrease and Venus will wax toward a gibbous phase shape before we lose sight of it later this year as it approaches 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.

Venus Is Brilliant

   In the post yesterday I mentioned that observing Venus daily through December would show Venus increasing in apparent size and decreasing, waning, in its phase shape. An interesting result of this is that at some point in this part of the orbit Venus will be as bright as it can be at any time during its orbit around the Sun. Today, 6 December, Venus will be shining at an apparent magnitude of -4.90 with approximately 26% of Venus illuminated by the Sun as shown by the banner graphic at the top of the page. Today our Moon will be approximately 21% illuminated allowing the two, Moon and Venus, to look very similar in phase appearance.

Venus and our Moon: 5 December to 11 January

Venus and our Moon: 5 December to 11 January

   This animated graphic shows Venus and our Moon on a daily basis (one frame = 1 day) starting on 5 December and ending on 11 January when Venus is at inferior conjunction. As Venus orbits closer to us it will continue to increase in apparent size and decrease phase shape until it reaches inferior conjunction, between the Earth and the Sun.

   
   
   
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.