Archive
09/07/11 – Ephemeris – The bright planets visible this week
Wednesday, September 7th. The sun will rise at 7:11. It’ll be up for 12 hours and 56 minutes, setting at 8:08. The moon, 3 days past first quarter, will set at 3:23 tomorrow morning.
It’s Wednesday and time again to take a look at the whereabouts of the bright planets. The ringed planet Saturn will be barely visible in the west southwest in evening twilight. It’s near the bright star Spica to its left. Spica has a blue tinge, while Saturn is yellowish. It will set at 9:25 p.m. Because we are seeing Saturn in evening twilight now its image is being deteriorated by the earth’s atmosphere being low in the sky. Jupiter will rise at 10:10 p.m. in the east northeast and is seen against the stars of the constellation Aries now. Mars will rise at 2:36 a.m also in the east northeast and is now passing through the constellation Gemini the twins. Mercury is briefly visible now from about half an hour after its rising in the east at 5:43 until about 20 minutes before sunrise.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
09/05/11 – Ephemeris – Mercury is visible in the morning
Labor Day, Monday, September 5th. The sun will rise at 7:09. It’ll be up for 13 hours and 2 minutes, setting at 8:12. The moon, 1 day past first quarter, will set at 1:13 tomorrow morning.
The planet Mercury is now very low in the eastern sky before sunrise. This tiny planet was at its greatest apparent distance from the sun yesterday. Astronomers call it greatest elongation and its separation from the sun was an 18 degree angle. Mercury will be very close to the east northeast horizon in the 6:30 a.m. twilight. Once found, you can probably follow it for the next 20 minutes or so. Mercury will be visible for the next week of so. The cool thing is that it will become brighter. It’s illuminated by the sun, and as it moves away from us around the sun its phase or illuminated portion from our vantage point becomes larger. Currently Mercury is being studied up close by the MESSENGER spacecraft now orbiting it.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Mercury in the morning in early September 2011. Chrat created using Stellarium.
08/16/11 – Ephemeris – Solar conjunctions today of Mercury and Venus
Tuesday, August 16th. The sun rises at 6:45. It’ll be up for 14 hours and 0 minutes, setting at 8:46. The moon, 3 days past full, will rise at 9:38 this evening.
Today we have an interesting coincidence. Both Venus and Mercury will be in conjunction with the sun. Astrologers may make a big deal out of it but this time astronomers won’t. A conjunction means that two solar system bodies are just north and south of each other. At 8:07 this morning Venus will be just north of the sun in superior conjunction. That is it is beyond the sun. And at 9:03 this evening Mercury will be somewhat south of the sun in inferior conjunction. Thai is it is between the earth and the sun. Mercury will be going into our morning sky, while Venus will begin to appear in the evening sky later this fall. But the coolest thing of all will be Venus’ next inferior conjunction June 6th, 2012. It will cross the face of the sun in a rare transit.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
05/13/11 – Ephemeris – Astronomical meaning of the morning planet lineup
Friday, May 13th. Today the sun will be up for 14 hours and 43 minutes, setting at 9:01. The moon, 3 days past first quarter, will set at 4:09 tomorrow morning. Tomorrow the sun will rise at 6:16
The planet grouping that’s now breaking up in the morning twilight might be taken as having meaning by astrologers. To astronomers it’s just a nice line up of planets, that is along our line of sight. Let’s look at their distances from the earth. Mercury is actually closest of the four now at 86 million miles, The rest are farther than the sun. Venus is next farthest at 139 million miles. Next comes Mars at 214 million miles away. Finally there’s Jupiter at 541 million miles out. So these planets are grouped by accident of their directions from the earth. They are not really close together. As far as influence goes, the moon, Jupiter and Venus gave the greatest gravitational effect of the earth, but that’s miniscule compared to the sun.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Line of sight of the planets in the Planet Jam for May 13th.
Here’s the animation of the morning planets this month.
Planet Jam May 2011 animation
05/04/11 – Ephemeris – The bright planets this week
Wednesday, May 4th. The sun rises at 6:28. It’ll be up for 14 hours and 21 minutes, setting at 8:50. The moon, 1 day past new, will set at 10:39 this evening.
It’s Wednesday and time again to take a look at the whereabouts of the bright planets. The ringed planet Saturn will be visible in the southeast as it gets dark. It’s near the bright star Spica to its lower left. Spica has a blue tinge, while Saturn is yellowish. It will cross the meridian due south at 11:40 p.m. and will set at 5:33 a.m. Our only other planet really visible is Venus which will rise at 5:34 a.m. in the east. Rising at 5:42 will be Mercury, followed a minute later by Jupiter. Dimmest is Mars, rising at 5:46. This is what I call a Planet Jam. If you can find Venus in the twilight and follow it until 7 a.m., you just might be able to spot Jupiter and Mercury. Mars will be problematic because it’s so dim.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
05/02/11 – Ephemeris – The “Planet Jam”
Monday, May 2nd. The sun rises at 6:31. It’ll be up for 14 hours and 16 minutes, setting at 8:48. The moon, 1 day before new, will rise at 6:21 tomorrow morning.
This month there will be a great gathering of planets in the morning sky, I call it a planet jam, kind of like a traffic jam. But these four planets are nowhere near each other, but just lined up to our sight. Unfortunately the group is too close to the sun and in the bright twilight to easily spot. The farther south you are the better the view. By south I mean south of the equator. Venus and Jupiter will be the easiest to spot, and by the end of the month Jupiter will break out of the group to become easily visible. Yesterday Jupiter passed Mars and within one day during the night of May 10th and 11th Venus will be in a tight group with Jupiter and Mercury. That morning might be the best time to spot Mercury. That’s half an hour before sunrise.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Planet Jam May 2011 animation
30 minutes before sunrise Eastern time is U.T. minus 4 hours. It’s perhaps a good thing I can’t ass the twilight glow. It’d drown out the planets.
03/17/11 – Ephemeris – MESSENGER spacecraft arrives at Mercury tonight
Ephemeris for St. Patrick’s Day, Thursday, March 17th. The sun will rise at 7:51. It’ll be up for 11 hours and 59 minutes, setting at 7:50. The moon, 2 days before full, will set at 6:48 tomorrow morning.
This evening the MESSENGER Spacecraft will fire its main engine for 15 minutes to put itself in orbit of the planet Mercury. The rocket firing will be at 8:45 this evening. Due to light time delays caused by Mercury being 97 million miles away, we won’t know if the rocket fired until 8:54. While its high gain antenna won’t be pointed at earth, we should get a signal from its omni- directional antenna. We did get a signal from Cassini with its orbital insertion of Saturn in 2004, and that was nearly a billion miles away. I don’t know if NASA TV’s covering the insertion live, but Johns Hopkins Applied Physics Laboratory is having a live webcast. Google “messenger mercury live orbital insertion” It was the first hit. I’ll have the address on the blog. http://messenger.jhuapl.edu/mer_orbit.html
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
What we used to know about Mercury
On Thursday evening, 8:45 p.m. March 17 EDT (12:45 a.m. March 18 UTC) the MESSENGER spacecraft will complete the second of NASA’s 2011 planetary trifecta when it will, if all goes well, fire its rocket engine to drop into orbit of the tiny planet Mercury. We’ve had six quick peeks at Mercury so far. Three by the Mariner 10 spacecraft in the 1970’s which looked at the same half of the planet due to Mercury’s unique rotational period. And three more by MESSENGER as it used Mercury to put on the breaks, so it would be going slow enough this time, so it’s rocket engine could drop it into polar orbit of the planet.
At first blush, Mercury looks like the moon. But it’s not. The moon is light, being made up, apparently, of mostly the crustal materials expelled by the earth and another Mars sized body. So it has a relatively small core. Mercury, on the other hand has a large core, and is the second densest planet at 5.43 grams per cubic centimeter. It’s only beaten out by the earth’s 5.52 g/cm3.
We’re going to learn a lot more about Mercury in the next year or so as MESSENGER maps Mercury and the complex interaction between it and the solar wind and magnetic field coming from the sun. Lets look back at the early history of our knowledge of Mercury.
It seems the that early Greeks noticed this elusive planet. They saw it in the morning sometimes, and then they saw it in the evening. At first they thought it was two separate planets that they gave the name Hermes in the evening and Apollo in the morning before they figured out that it was the same planet. The name Mercury we know the planet by today is the Roman equivalent of Hermes.
Another revelation came later. In my youth Mercury was thought to be in tidal lock with the sun, like our moon is to the earth. The rather poor markings found on the planet seen low in the sky at dusk and dawn seemed to bear that out an 88 day rotation to match its 88 day revolution of the sun. It wasn’t until 1965 that radar observations proved that the rotation was 2/3 of 88 days. Every 2 orbits of the sun Mercury rotates 3 times. It seems that the best times to spot Mercury are when it’s in the same part of its orbit, but basically every other return to that spot. Funny thing. The northern hemisphere’s best views of Mercury are for its eastern elongation on spring evenings and western elongations on autumn mornings. In effect we’re viewing Mercury at the same point in its orbit, when it is near its perihelion, when it is closest to the sun. The southern hemispheric observers get to see more favorable views of Mercury, when it’s farthest from the sun.
As we’ve found with all the planets that we’ve gotten a close look at, the generalities of our long-standing ignorance is brushed away. Each planet is its own unique place in the sun.
Taken from my March, 2011 article in the Stellar Sentinel,the newsletter of the Grand Traverse Astronomical Society.
Here is the MESSENGER web page. This mission is run for NASA by the Johns Hopkins Applied Physics Laboratory.
MESSENGER’s First Look at Mercury’s Previously Unseen Side
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Bob Moler's Ephemeris Blog 