Dance of the Planets

   Over a period of the next two weeks the planets Venus, Uranus, and Mars are all more or less in the same direction, or line of sight as we see them in the evening skies. Not an alignment straight out from the earth, but rather they are arranged along the ecliptic from west to east. From an overhead view you can see that the three planets are at a point along their respective orbital path where they are viewed in the same direction.

   Since the planets are in motion, as also is the Earth, The three planets, Venus, Uranus, and Mars will all come together in conjunctions beginning with a triple conjunction on March 4th when the three will easily fit within the field of view of binoculars as they graphic shows. On that day the ‘gap’ between Venus and Uranus will be 0.09o making this the closest planet-planet conjunction for the year.
Then on March 11th Mars and Uranus will be in a planet-planet conjunction and they will be separated by 0.27o. This will be close enough to fit both within the field of view of a 25mm eyepiece in an 8″ Reflecting telescope.

February 28th to March 15th

February 28th to March 15th at 7:30pm CST and CDT)

   This animated graphic (with greatly exaggerated planet size and separations) is set to 1-day intervals. In addition to the motions of the planets relative to each other the part of the sky where the conjunctions take place is gradually getting closer to the horizon and the Sun. This is a result of the Earth’s orbital motion causing the sky to shift toward the west each day and the Sun’s apparent eastward motion.

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-Saturn Conjunction Series

Venus and Saturn 17-23 September

Venus and Saturn 17-23 September

   This evening and for the next several evenings look between the southwestern and western horizons for the very bright inner planet Venus. Just above Venus is the not nearly as bright outer planet Saturn as the page banner shows –which by the way is not drawn to scale. In this animated graphic set for 1-day intervals, Venus is moving eastward and will pass Saturn, which is also moving eastward.
   Both of these planets are in motion as each is moving at its own speed eastward as we view them from the Earth. The Sun is also moving eastward but this is an apparent motion caused by the Earth revolving around the Sun. The net result of the Earth’s actual motion and the Sun’s apparent motion is that the area of the sky where the two planets are located is moving westward and setting a bit earlier each evening. The Sun’s apparent daily motion eastward from revolution (not rotation) is at the Earth’s daily orbital rate of approximately 1 degree per day which is faster than Saturn’s daily orbital rate of approximately 0.035 degrees per day. So Saturn and its part of the sky shifts westward while Saturn is moving eastward from its own orbital motion, but obviously slower than the Sun’s apparent motion.

Venus and Saturn 17-23 September

Venus and Saturn 17-23 September

   In this simulated 7×50 binocular view of the two planets you can again see how the two planets respective daily orbital rates compare. And as you watch, the star Zubenelgenubi, a near 3rd magnitude star in the constellation Libra, moves from left to right (east to west) into the scene. Since we consider stars to be fixed objects in the sky (actually they all do have their own motions) we could use Zubenelgenubi as a means of comparing the relative speeds of these objects.

Click on picture to see it full size.

Click on picture to see it full size.

   What would really add to this conjunction would be to have the crescent Moon as part of it as was the situation on the evening of 1 December 2008 when the waxing crescent Moon, Venus, and Jupiter joined for a triple conjunction. This was taken with my older 6 megapixel Canon Powershot Camera on a tripod with the aperture set to F8; shutter speed to 1-second, and ISO was on automatic.

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

Dance of the Planets

23 May to 11 June - 8:30 pm CDT

23 May to 11 June – 8:30 pm CDT

   In my posting yesterday I described the orbital motions of these three planets without the use of a graphic to help visualize that explanation. This animated graphic that is set to one-day intervals starts with today’s date and then runs for a few weeks. This gives enough time to see how both Mercury and Venus are moving eastward while it appears that Jupiter is moving in the opposite direction, west towards the Sun. Jupiter is in fact moving eastward but considerably slower than the Sun’s apparent eastward motion. The net effect is that Jupiter sets earlier and earlier as the Sun gets closer, and eventually Jupiter moves behind the Sun.

   Both Mercury and Venus were recently on the opposite side of the Sun from the Earth at superior conjunction. Coming from that relative position both planets travel eastward until they reach a point with respect to the Sun that we see as the furthest apart, or the greatest angular separation between the Sun and Mercury or Venus. This happens on either side of the Sun and are known as elongations. Since both planets are on the east side of the Sun they are both heading toward eastern elongation. In the animated graphic above you can see all of Mercury’s orbit on the east side of the Sun including the part where Mercury reaches eastern elongation and heads back toward the Sun. Because Venus is further from the sun it has a longer orbital period around the sun and likewise a longer orbital path so Venus’s orbital path on the graphic extends past the edge.


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

Stairway to the Horizon

7:00 a.m. CST - 8 December

7:00 a.m. CST – 8 December

   The waning Moon this morning was poised to start the first of several conjunctions with planets and a star over the next few mornings. Go out around sunrise your local time each mornig and look toward the southeast horizon for the Moon as it sort of stair-steps its way toward the horizon.
   The Moon is also passing through a part of the sky housing a menagerie of characters including a Harvest Maiden, a Crow, a Wine Goblet, an Equal Arm Balance, and of course a many headed snake! Click here to see a graphic illustrating what I am writing about.

Sunrise - 9 December

Sunrise – 9 December

   The Moon will be near the blue-white star Spica in Virgo the Harvest Maiden on Sunday morning 9 December.
Sunrise - 10 December

Sunrise – 10 December

   The Moon will be near the planet Saturn on Monday morning 10 December.
Sunrise 11 December

Sunrise 11 December

   The Moon will be near Venus and Mercury on Tuesday morning 11 December.

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

Venus and Regulus Are ‘Tight’ With ISS

Animation Set to 1-Day Intervals (Oct. 1 to 6)

Estimated Local Time

    For the past few weeks the planet Venus has been steadily moving eastward toward the Sun. It is now closing in on the star Regulus in Leo the Lion. This coming Wednesday, the 3rd, Venus will be about 0.15o from Regulus – so close that to the naked-eye they may seem as one star. Venus is very bright at a magnitude of -4.0 compared to a magnitude od 1.3 for Regulus. At the least the brightness of Venus will ‘overshadow’ Regulus.
    ISS Watch: This week there will be several opportunities for catching a look at the International Space Station. And on the morning of the 3rd there will be two opportunities about 90 minutes or onnce around the Earth at Space Station speeds!

ISS- Venus – Regulus

    The first pass, for my area, at around 0512 am CDT, will only be about 1 minute but it will take the ISS across the horizon past the stars of the Big Dipper and coming very close to Venus and Regulus.
    Ninety-four (94) minutes later, at 0646 am CDT, the ISS will again be visible, this time for around 5 minutes. However the sky will be considerably brighter but the ISS is very bright and should still be visible.
    I use the NASA web site, ISS Sightings, to get the times when the ISS as well as the supply vessels will be visible from my home. The web site calculates for many countries, states, and cities, and the times are very accurate. It is easy to find your home city or town, or the nearest one.
    I then use the Starry Night Astronomy program to get visual information as well as the graphics I use for the pictures and animations.
    A fun thing to do is take someone who has never seen the ISS outside and at the right moment say look there as you point to where the ISS first becomes visible above the horizon.
    An alternate to the NASA web site is the Heavans Above web site.
    Here is a short video clip showing the two ISS passes for my area.

Moon on the Move

Moon Near Saturn

This evening the waxing crescent Moon is within a few degrees from the planet Saturn. Look toward the western horizon at sunset to see this conjunction. Tomorrow evening the waxing crescent Moon will be near Mars at about the same time.
Take advantage of the viewing opportunity as this will be the last Saturn – Moon conjunction in the evening skies until next year. Why? The Sun in its apparent motion along the ecliptic is catching up to Saturn and within the next couple of weeks Saturn will be too close to the Sun for viewing. Saturn will re-appear as a morning planet by the end of the year and will then continue its regular monthly pattern of conjunctions with the Moon, although it will be with the waning crescent Moon at sunrise.