Mars during the 2005 oppositionToday the planet Mars will be at its closest point to the Earth.
Mars was at opposition two days ago, but not at its closest. Close approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year sees the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST. At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.
All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.
Mars during the 2005 oppositionToday the planet Mars will pass through opposition.
Closest approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year closest approach will occur March 5th with the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST. At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.
All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.
Today is February 29th, that odd date that only occurs every four years.
The reason for a leap day inserted into the calendar, the existence of February 29th, is ultimately astronomical. Perhaps a little explanation is in order…
We originally defined days as the time it takes the Earth to rotate. While we define years as the time it takes the Earth to orbit once around the Sun. The problem is that these values do not divide evenly into one another.
Sunrise seen from the summit of Mauna KeaThe Earth takes about 365.24219 days to obit the Sun, when measured by the Sun’s position in the sky, what is called a tropical year. There are different ways to measure a year, but if one is concerned with keeping the seasons in sync with your calendar, then you are interested in tropical years.
It is that bunch of decimals, the 0.24219 etc., that is the problem, every four years the count drifts out of sync by roughly one day. The insertion of an extra day every four years helps bring the calendar back into synchronization with the orbit of the Earth and with the seasons.
Even leap years do not quite fix the problem as 0.24219 is close, but not quite 0.25 or one quarter of a day. Thus additional corrections are needed… Enter leap centuries.
Our current calendar was instituted by Pope Gregory XIII in 1582, setting up a standard set of corrections for the fractional difference between the length of a year and the length of a day. Scholars knew that errors had been accumulating in the calendar for centuries, resulting in a drift of several days. Religious authorities were concerned that this drift had displaced important celebration in the church calendar, in particular the celebration of Easter. After much argument it was decided to reform the calendar. The current solution was devised by a number of astronomers, including Aloysius Lilius, the primary author of the new system.
The Gregorian Calendar uses an extra day in February every four years, unless the year is divisible by 100, then there is no leap leap day that year. However, if the year is divisible by 400, then it is a leap year. While this may sound odd, it does create a correction much closer to the ideal value of 365.24219 days per year.
Even this is not perfectly precise. The correction is close but will drift given enough time. The length of a tropical year also changes slowly over time. We will eventually have to add another correction to keep the calendar and the seasons in sync. But not for a few millennia, good enough, for now.
As 2012 is divisible by four, there will be a leap day added to the end of this February… Today.
One week from today, on March 3rd, the planet Mars will pass through opposition.
Mars orbits the Sun every 1.88 years, with Earth only taking one year for each orbit. Like two runners on a track the two planets race each other around the Sun. But we have the inside lane, lapping the red planet every two years. These events are called opposition, when Mars is closest to us and best positioned for viewing by earthbound telescopes.
Closest approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year closest approach will occur March 5th with the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST.1 At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.2
Mars during the 2005 opposition
Do not worry about viewing on the 3rd or 5th, any time in the month leading up to and after opposition the viewing will be very good. With even a modest telescope it should be possible to see the bright polar caps and light and dark markings on the planet.
All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.
About a month from today, on March 3rd, the planet Mars will pass through opposition.
Mars orbits the Sun every 1.88 years, with Earth only taking one year for each orbit. Like two runners on a track the two planets race each other around the Sun. But we have the inside lane, lapping the red planet every two years. These events are called opposition, when Mars is closest to us and best positioned for viewing by earthbound telescopes.
Closest approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year closest approach will occur March 5th with the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST.1 At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.2
Mars during the 2005 opposition
Do not worry about viewing on the 3rd or 5th, any time in the month leading up to and after opposition the viewing will be very good. With even a modest telescope it should be possible to see the bright polar caps and light and dark markings on the planet.
All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.
Does the Moon seem a little larger and brighter than usual? It may not be an illusion, sometimes the Moon really does look a little larger or smaller in the sky.
Like all orbiting objects, the Moon does not orbit in a perfect circle, but rather in an ellipse. This means that as it orbits it is a little further away or a little closer. In the case of the Moon the difference is not much, but you can see it, if you know to look.
The apparent size of the moon as seen at perigee versus apogeeWhen the Moon is furthest from the Earth, a point called apogee, it will be about 405,000km (251,000miles) from the Earth. While at perigee, the Moon will be about 360,000km (223,000miles) from the Earth, as measured from the center of the Earth to the center of the Moon. The change in distance leads to a noticeable difference in the size of the Moon as seen by an observer here on Earth. When at perigee the moon will appear about 12% larger than when seen at apogee.
Click to view a simulation of a lunar month showing phase, libration (tilt), and the size change as the Moon goes from apogee to perigee. Image credit Tomruen via Wikimedia CommonsThe difference is most noticeable at full Moon. If the full Moon occurs near apogee or perigee, an experienced skywatcher can spot the difference. The effect should not be confused with the well known Moon illusion, where the Moon can appear larger near the horizon.
The period of time between full Moons, the synodic month, is about 29.5 days. While lunar perigee occurs every 27.5 days, an anomalistic month. Since these periods are not equal, the cycle drifts in and out of phase. About once a year the cycles coincide and full Moon and apogee or perigee will occur near the same time.
At apogee, the Moon will be appear about 29 arc-minutes in size, a little less than half a degree. At perigee the Moon will be about 33 arc-minutes across, a bit more than half a degree. The numbers may not seem like much, but it is a visible difference. The simulated images shown here will give a better idea of what the numbers represent.
This change in size and distance leads to the moonlight being a bit brighter at perigee than at apogee, about a 30% difference. So if that moonlit night seems brighter than you remember it may actually be the case.
As a planet moves across the sky there are particular points in its orbit that describe the motion, part of the jargon of astronomy that can confuse the uninitiated. These terms do not represent anything difficult, you just have to visualize what they mean. Understanding the movements of planets across the sky gives a little insight into our beautiful universe.
Elongation, opposition and conjunctions, the apparent positions of a planet with respect to the EarthThe terms used commonly here on Darker View are ideas that date back to the early beginnings of astronomy. Those ancient astronomers were fascinated by the movements of the bright wandering stars, the planets. They tracked and recorded the motions meticulously and invented the terminology we still use today to describe those motions.
Superior Conjunction, Inferior Conjunction, Opposition and Maximum Elongation tell any experienced skywatcher exactly where a planet is with respect to the Earth, where it is in our sky, and where it will be in the coming weeks or months. It is all part of the intricate patterns of our solar system that allow anyone who learns to become familiar with the night sky.
Today the Earth is closest to the Sun, a point called perihelion. We will be about 147,098,290km (91,402,639miles) from the Sun. Compare this to the 152,098,232km (94,509,459miles) we will be at aphelion on July 4th, a difference of about 5,411,169km (3,362,344miles) occurs throughout one orbit.
It may seem odd that we are actually at the closest for the middle of northern winter, you just have to remember that proximity to the Sun is not the cause of the seasons. The seasons are caused by the axial tilt of the Earth, creating short and long days throughout the year, with a resulting change in the angle and intensity of the sunlight.
