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07/30/2018 – Ephemeris – Early tomorrow morning Mars will be the closest to is in 15 years

July 30, 2018 Comments off

Ephemeris for Monday, July 30th. The Sun rises at 6:26. It’ll be up for 14 hours and 44 minutes, setting at 9:10. The Moon, 3 days past full, will rise at 10:51 this evening.

Mars’ closest approach to the Earth since August 27, 2003 is tomorrow at about 3:51 a.m. at a distance of 35.8 million miles (57.6 million km). The last really close approach of Mars was on August 27, 2003 when it was about 600 thousand miles (a million km) closer. That close approach was probably the closest in 50 thousand years. Mars and the Earth get close in their orbits about every 26 months. But because Mars has a much more elliptical orbit than the Earth, the very best close encounters occur every 15 or 17 years. Despite the fact that we have satellites that orbit Mars and two rovers operating on its surface, amateur astronomers still challenge themselves to observe and photograph Mars at its very closest.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Mars closest approaches 2003-2018

Mars’ closest approaches to the Earth in the period 2003 to 2018 also showing the apparent sizes of the planet at each approach. Click on image to enlarge. Created using my LookingUp program and Cartes du Ciel (Sky Charts).

 

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07/26/2018 – Ephemeris – How can you get to Mars – the Hohmann transfer orbit

July 26, 2018 Comments off

Ephemeris for Thursday, July 26th. The Sun rises at 6:22. It’ll be up for 14 hours and 53 minutes, setting at 9:15. The Moon, 1 day before full, will set at 6:06 tomorrow morning.

How does one get a spacecraft to another planet, like Mars? One might think to wait until the two planets are closest and zip across. That would take more energy than we are capable of. We cab barely escape the Earth and get a spacecraft into solar orbit. Also one needs energy to slow down to be captured by the planet if one wants to orbit it. The most economical way was devised way before the space age by Walter Hohmann, a German scientist in 1925. The idea is to launch a spacecraft with enough velocity to reach the other planet half way around the Sun, so the transfer orbit is tangent to both the Earth’s and the planet’s orbit. Transit times to Mars would be in the range of 7 months. The InSight lander is currently on such a trajectory.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Hohmann transfer orbit

Hohmann transfer orbit. Credit Planetary Society-Myron Kayton

Hohmann orbit to Mars

A Hohmann lowest energy transfer orbit to Mars. This diagram is for the Mars Exploration Rovers Spirit and Opportunity orbits, launched in 2003, arrived in 2004. Solid planets, Spirit launch and arrival. Ghost planets, Opportunity launch and arrival. Credit NASA/JPL.

07/23/2018 – Ephemeris – The importance of Mars in determining the nature of the solar system

July 23, 2018 Comments off

Monday, July 23rd. The Sun rises at 6:19. It’ll be up for 14 hours and 59 minutes, setting at 9:18. The Moon, half way from first quarter to full, will set at 3:41 tomorrow morning.

The accurate observational positions of Mars by Tycho Brahe allowed Johannes Kepler in the early 17th century to discover his three laws of planetary motion. Tycho was the last and greatest of the naked eye astronomers. Kepler befriended Tycho who jealously guarded his observations. It was only after his death in 1601 that Kepler took possession of Tycho’s data. Until then it was believed that planets moved with uniform circular motion, even though they didn’t look like it. Astronomers added circle after circle, called epicycles, to attempt to make their system work. Mars was the worst case. Kepler finally determined that Mars, and indeed all the planets, orbited the Sun in elliptical orbits. That was his first law of planetary motion.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The source if the images below is the talk “Mars 2018” I gave at the Betsie Valley District Library, July, 20, 2018.

Tycho and Kepler

Tycho and Kepler. Artist for Tycho: Eduard Ender (1822-1883). Artist for Kepler, unknown. Source: Wikipedia.

Mars and Earth's orbits

Mars’ and Earth’s orbits to scale and positions of the Earth and Mars July 20, 2018, one week before opposition. Note that Mars’ orbit is decidedly not circular. Credit my LookingUp program.

Retrograde Mars Path 2018

Created using Cartes du Ciel (Sky Charts).

Retrograde motion explained

Created using Cartes du Ciel (Sky Charts).

05/24/2018 – Ephemeris – Jupiter is really BIG

May 24, 2018 Comments off

Ephemeris for Thursday, May 24th. Today the Sun will be up for 15 hours and 8 minutes, setting at 9:14, and it will rise tomorrow at 6:05. The Moon, 3 days past first quarter, will set at 4:24 tomorrow morning.

Jupiter is a big planet. How big is it? One could fit thirteen hundred Earths inside it. Even so Jupiter has the mass of only 318 Earths, so Jupiter is made of lighter stuff than the Earth, including a lot of hydrogen and helium. NASA’s Juno spacecraft is currently orbiting Jupiter, working that out. Still, Jupiter is massive. The late science and science fiction writer Isaac Asimov wrote that the solar system consists of the Sun, Jupiter and debris. Jupiter contains more than twice the mass of all the other planets and asteroids combined. Jupiter is also surrounded by a huge set of radiation belts, lethal to all but the most radiation hardened spacecraft. And that goes for would be astronauts too.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Planet size comparison

Planet size comparison. Note that even though Saturn looks almost as large as Jupiter it is less than 30% of Jupiter’s mass. From connormorency.wordpress.com

05/08/2018 – Ephemeris – Jupiter at opposition

May 8, 2018 Comments off

Ephemeris for Tuesday, May 8th. The Sun rises at 6:23. It’ll be up for 14 hours and 33 minutes, setting at 8:56. The Moon, 1 day past last quarter, will rise at 3:45 tomorrow morning.

At 8:10 p.m. Jupiter will be in opposition, that is opposite the Sun in the sky. Thursday at 8 a.m. it will be its closest to the Earth at 408.9 million miles away, and its biggest in telescopes at 44.8 arc seconds. The Moon averages about 1,800 arc seconds in diameter. So the Moon appears 40 times larger in diameter, meaning you could put 40 Jupiters across the diameter of the moon. Jupiter’s disk is visible in binoculars, along with several of its moons. The moons change position from night to night. Most computer planetarium programs will show the moons for any time past and future. Telescopes will reveal that Jupiter’s face is crossed by bands of contrasting colors of clouds, and the famous Great Red Spot.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Jupiter with its Great Red Spot

Jupiter with its Great Red Spot November 18, 2012 by Scott Anttila.

05/07/2018 – Ephemeris – Twilight

May 7, 2018 Comments off

Note:  Sorry for the delay.  I was hit with a fast developing cold Sunday.  So I was unable to post this at my normal time, and was unable to record my next Tuesday through Monday programs.

Ephemeris for Monday, May 7th. The Sun rises at 6:24. It’ll be up for 14 hours and 30 minutes, setting at 8:55. The Moon, at last quarter today, will rise at 3:14 tomorrow morning.

We are in the time of year when it appears that twilight doesn’t seem to end. There are three definitions of twilight, Civil, Nautical and Astronomical. Each ends in the evening when the Sun is 6, 12, and 18 degrees below the horizon respectively. Astronomers don’t really care about civil twilight, the sky is too bright. Sailors using a sextant for star positions can usually see the horizon for star sighting up to the end of nautical twilight. Astronomers consider the skies dark at the end of astronomical twilight, barring he Moon being up. The brightest stars and planets become visible a half hour after sunset. We begin to pick out constellations at the end of nautical twilight. For instance, for tonight, nautical twilight ends at 10:10 p.m., while astronomical twilight ends at 10:57.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Categories: Concepts, Ephemeris Program Tags:

04/30/2018 – Ephemeris – Venus-Earth resonances, and Jupiter & the Moon tonight

April 30, 2018 Comments off

Ephemeris for Monday, April 30th. The Sun rises at 6:34. It’ll be up for 14 hours and 12 minutes, setting at 8:46. The Moon, 1 day past full, will rise at 9:30 this evening.

Jupiter will be near the moon tonight. The gravitational force between the planets produces some interesting resonances in their orbital periods. Venus has three different kinds with the Earth. First, Venus orbits the Sun 13 times in the same time it takes the Earth to orbit the Sun 8 times. This is a 13 to 8 resonance. This sets up the 5 Venus Cycles equaling 8 years resonance the Mayan’s discovered. A Venus cycle of 584 days takes Venus to go from Morning Star to Evening Star and back again. The next one wasn’t discovered until we started to bounce radar signals off Venus. We found it rotates backwards, and very slowly at that. Its rotation with respect to the stars is longer than its year. And it so happens that every passage near the Earth the same side of Venus is facing us.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The Moon and Jupiter

The Moon and Jupiter at 10 p.m. tonight, April 30, 2018. Created using Stellarium.