September Qué tal Now Available

   Many interesting celestial events this month including minor meteor showers, the September equinox, and conjunctions with our Moon, planets, and stars. Venus and Saturn and the star Spica have some close conjunctions in the evening skies at sunset. In the east before sunrise look for Jupiter to be the point of a triangle with the twin stars. Mars will pass through M 44, the Beehive Cluster, an open star cluster in Cancer.

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

Moon and Star Clusters

Click on image to see full size.

Click on image to see full size.

   Before sunrise on Friday morning 30 August look toward the east for the group of stars and constellations making up a familiar part of the northern hemisphere winter skies. Part of this group, temporarily, is the waning crescent Moon as it works its way eastward. The Moon will be within the field of view of 7×50 binoculars from two open star clusters. M-35 is an open star cluster that is approximately 2800 light years distant and contains several hundred stars shining with a combined brightness of around 5th-6th magnitude.
   Just one-half degree from M-35 is the much fainter star cluster NGC-2158.
Click on image to see full size

Click on image to see full size.

This is a much smaller and fainter group of stars that are estimated to be around 11,000 light years distant and has an apparent magnitude of between 8 and 9.
   Click here to go to the Qué tal in the Current Skies web site for more observing information.

Not Really – Or Really??

tyson   I found this on Facebook this morning and was surprised not only by what I consider misinformation but also that is supposdly from Neil DeGrasse Tyson, a respected and well liked Science entertainment personality.
   For a clarification the sun does not have enough mass to explode, I guess as in a supernova event. And there is not a companion star losing mass to the surface of the Sun which would lead to a nova event. So while I guess this is an entertaining notion I think it would have made more sense to suggest that if somehow the Sun were to switch off we would not know for 8 minutes or so because at the speed of light it takes about 8 minutes for light from the Sun to reach the Earth. At the end of the 8 minutes it would get dark!
   What I am not too sure about is describing gravity as having speed. I would think that since gravity is universal it is always there – everywhere – not traveling between objects as light or other radiation does. We are able to measure the rate of acceleration due to gravity between objects but is that the same as a speed of gravity?

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

Mars Madness?

   This year, during August, Mars will be at its closest to the Earth; so close, in fact, that it will appear as large as the full Moon.
   Have you heard this urban legend before? According to some tomorrow, the 27th, it will happen again. For the record the full Moon was the 21st, not that the Moon needs to be visible for this non-event. Consider that since 2003, emails describing this urban myth have circulated the internet usually during July or August. It all started during the opposition of August 2003 when Mars was about as close as it can be to the Earth (55,755,723 km [34,645,000 mi.]) in a 20-year cycle of varying distances at opposition. Since then, usually around August, misinformation about the appearance of Mars circulates around the internet.

Mars and Earth 3 March 2012 and 27 august 2013

Mars and Earth 3 March 2012 and 27 august 2013

   The outer planets reach opposition when the Earth has moved into a position with the Sun on one side and the outer planet on the other side. Because all planets orbit in the same direction (toward the east), and all follow orbits that are slightly more elliptical than circular, oppositions occur at regular intervals of about 12 months (except for Mars). Mars is considerably closer to Earth and is moving faster than the other outer planets, so it takes approximately 26 months for Earth to catch up with Mars for an opposition. In the time that it takes the Earth to catch up with and move into an opposition position, the outer planets have also been moving eastward relative to the stars in the background. Over time, the constellation where the outer planet is located during opposition and its retrograde loop gradually shift to the east. An opposition is also near the time when the distance between the Earth and an outer planet is around the minimum distance. Keep in mind that because the shape of the orbit is elliptical, this minimum distance will be different each time.
Click on image to see full size

Click on image to see full size

   Since opposition for Mars was March last year (2012) and not during August as it was during August 2003, this should help dispel this particular urban myth that has appeared every July or August since that August 2003 opposition. However, there is an even more conclusive way to show that Mars could never be so close that it would appear as large as the Moon. To see how use the information in the data table and the math formulas below. You will see that Mars could not appear to be as large as our Moon unless some force somehow caused Mars to change its orbital position and literally move closer to Earth.
   On March 5, 2012, Mars was 100,781,093 km (62,622,472 mi.) from Earth. Mars is 6,792 km (4,220 mi.) in diameter. The Moon is 3,475 km (2,159 mi.) in diameter and is an average 384,400 km (238,900 mi.) from Earth. To calculate other dates, use other distance (km) values from the data table and the math formulas:

To calculate how large Mars will appear as compared to the Moon:

(Mars’s diameter ÷ Mars’s distance) ÷ (Moon’s diameter ÷ Moon’s distance)

To calculate how close Mars would have to be to appear as large as the full Moon:

(Mars’s diameter × Moon’s diameter) × Moon’s distance

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

Preview September Qué tal

voki   As the subject line states, the September preview issue of Qué tal in the Current Skies is now online and available at this temporary web address: http://currentsky.com/2013/sep13/index.html
   It will be at its regular web address in a few days.

   Thank you for your support and encouragement.
   Clear Skies…
   Bob Riddle

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

Mercury Behind the Sun

19-31 August

19 to 31 August

   Today the innermost planet Mercury reaches the point along its orbit around the Sun where it is on the opposite side of the Sun from the Earth. This position is referred to as superior conjunction and all solar system objects orbiting the Sun will, at some point in their respective orbit, reach superior conjunction.
Click on image to see it full size

Click on image to see it full size

   Each frame of this animated graphic shows the planet Mercury at one-day intervals as the planet moves behind the Sun. We see Mercury from this perspective rather than as it is shown in the banner graphic at the top of the page. This is because the Earth and the other 7 planets all orbit the Sun on pretty much the same plane, or level.

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

Moon Uranus!

Click on image to see full size

Click on image to see full size

   Ok, so how can you Moon Uranus? Yeah I know – a sad, and bad joke. Let’s put it behind us.
   Seriously, late this evening, 23 August, the waning gibbous Moon rises within a few degrees from the planet Uranus. Both are within the eastern fish of the constellation Pisces the Fishes as the banner graphic at the top of the page shows. Uranus ‘shines’ at just under 6th magnitude so it is possible to see the 7th main planet from the Sun with binoculars. However the reflected light from the Moon will brighten the sky enough to drown out the dimmer light from Uranus and most other stars in the area making them not visible. So just remember this spot in the sky and also that the Moon rises about an hour later each day and after the Moon is no longer in the vicinity you should be able to pick out the planet.
   Click here to see a simulated star field as seen through 7×50 binoculars with the apparent magnitude for some of the stars around Uranus shown.

   
   Speaking of Uranus here is a portion of the Orbits performance video showing Uranus and some of its moons.

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

Sun Not in Virgo Today

Along the ecliptic with the Sun from 10 August until 14 September

Along the ecliptic with the Sun from 10 August until 14 September

   According to the pseudoscience of astrology the Sun enters the constellation of Virgo the Harvest Maiden today, 22 August. When in fact the actual position of the Sun today is within the boundary of the constellation of Leo the Lion, as the banner graphic at the top of the page shows. Leo is the constellation to the right, or west from Virgo. The Sun in its apparent motion along the ecliptic spends about 35 days traversing Leo.
   Read a little more about how astrology has the Sun incorrectly placed in a previous blog from last month, and an earlier blog discussing the effects of precession.
   
   
   
   Click here to go to the Qué tal in the Current Skies web site for more observing information.

August Perigee Moon

Click on image to see it full size

Click on image to see it full size

   Our Moon orbits around the Sun with the Earth and from our perspective on the Earth the Moon appears to circle the Earth each month. The Moon also has a slightly elliptical-shaped orbit allowing for the Moon to have a furthest (apogee) and closest (perigee) distances from the Earth each month. This month the 13.69 days old waxing Gibbous Moon reaches perigee today, 19 August, and will more or less be at a distance of 28.2 Earth diameters (360,065.0 km or 223,734.0 miles).

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

It’s About Mars

Click on image to see full size

Click on image to see full size

   Tomorrow morning, 17 August, an hour or so before sunrise look toward the eastern horizon for the planet Mars to rise with the constellation of the Gemini Twins. Mars will be less than 5 degrees from the the star Pollux and easily see together with Mars within the field of view of binoculars as the inset to the graphic on the right shows.
mars jupiter   Shortly after sunrise Mars will reach an interesting position in its orbit relative to the Sun and the planet Jupiter. Both Mars and Jupiter will be at heliocentric conjunction with each other. Both planets will be at approximately 93 degrees heliocentric longitude.

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