Perihelion

Earth’s perihelion will occur at 19:20HST today.

Sunrise over Georgia Strait
Sunrise over Georgia Strait

Perihelion occurs when the Earth reaches its closest distance to the Sun for the year.

It may seem odd to some the perihelion occurs in the middle of winter. One must recall that the distance from the Sun is not the cause of our seasons, that is the effects of axial tilt.

2019 Apsides and Seasons
Event Universal TimeHawaii Standard Time
Perihelion Jan 0305:20UTJan 0219:20HST
Spring Equinox Mar 2021:58UTMar 2011:58HST
Summer SolsticeJun 2115:54UTJun 2105:54HST
Aphelion Jul 0422:11UTJul 0412:11HST
Fall Equinox Sep 2307:50UTSep 2221:50HST
Winter SolsticeDec 2204:19UTDec 2118:19HST
Data from US Naval Observatory Data Services

Fly Over Jupiter

Take a series of photos from the Juno spacecraft and just project them in sequence to make a timelapse movie of the spacecraft swinging past Jupiter. Sounds easy… Right?

Not easy at all. As the spacecraft orbited past the planet the perspective changes rapidly. To make a natural seeming animation much more would have to be done. Mathematician Gerald Eichstaedt did just that… Taking 36 images he projected each image on a mathematically modeled sphere, then panned through each image using the orbital trajectory of the spacecraft to create a view to simulate actually being there.

Further work by filmmaker Seán Doran smoothed the resulting video into an even more natural view. This created the video posted below. You can see the original video at https://www.youtube.com/watch?v=AuOy-shbQuM&feature=youtu.be

The result is simply stunning, take look at what it would have been like to be there as Juno swung past the planet just a few thousand miles above the cloudtops.


Jupiter: Juno Perijove 06 from Sean Doran on Vimeo.

Comet? Where?

There is one question we all have to ask when a beautiful comet graces the skies…

C/2007 N3 Lulin
Comet C/2007 N3 Lulin on the evening of 26 Feb 2009
Where to look?

Like any other solar system object, comets move against the sky. Even worse, when close to the Earth or Sun they can be moving so quickly against the stars that coordinates quickly become out of date. Aiming a telescope using coordinates a day old, or sometimes even only an hour old will result in a view of empty sky. A few stars perhaps, but no comet.

You need a table of coordinated calculated for regular time intervals, an ephemeris. Alternately you need a set of coordinates calculated for the exact time you will be looking.

Continue reading “Comet? Where?”

Preparing for Comet C/2012 S1 ISON

Astronomers, professional and amateur alike, are getting ready for comet C/2012 S1 ISON, possibly the highlight of a year that has already seen several good comets.

Discovered in September 2012 by Vitali Nevski and Artyom Novichonok, of the ISON project, a group of telescopes dedicated to discovering and tracking solar system objects. The comet was then an 18th magnitude object in the outer solar system, an impressive find for a small telescope.

Comet C/2012 S1 ISON
An image of comet C/2012 S1 ISON acquired by the Hubble Space Telescope on October 9th, 2013, credit: NASA, ESA, and the Hubble Heritage Team
When astronomers first calculated the comet’s orbit they found a surprise. The comet will pass close to the Sun. Not just close, but extremely close! On November 28th the comet will pass perihelion, its closest approach to the Sun. At a mere 1,860,000km (1,150,000miles) this will be a close pass indeed. As perihelion is measured from center to center, the distance is even closer if you consider the 695,500km (432,200mile) radius of the Sun. Subtracting the solar radius you realize the comet will pass a mere 1,165,000km (724,000miles) above the surface of the Sun. At this distance the intensity of the solar radiation will be nineteen thousand times more intense than a sunny day on Earth.

The next surprise was hinted at by the orbital calculations. The orbital solution indicated a nearly hyperbolic path, suggesting that this was a new comet, one that had not visited the inner solar system before. This possibility was strengthened by later observations of the comet.

Continue reading “Preparing for Comet C/2012 S1 ISON”

Winter Solstice

Winter solstice occurs today at 01:12HST. Today the Sun will occupy the most southerly position in the sky of the year. The term solstice comes from the latin terms Sol (the Sun) and sistere (to stand still). On this day the Sun seems to stand still as it stops moving southwards each day and begins move to the north. This is the first day of winter as marked by many cultures in the northern hemisphere.

2012 Solstices and Equinoxes
  UT HST
Perihelion Jan 5 03:59UT Jan 4 17:59HST
Spring Equinox Mar 20 05:14UT Mar 19 19:14HST
Summer Solstice Jun 20 23:09UT Jun 20 13:09HST
Apehelion Jul 4 23:59UT Jul 4 13:59HST
Fall Equinox Sep 22 14:49UT Sep 22 04:49HST
Winter Solstice Dec 21 11:12UT Dec 21 01:12HST
 
Source: USNO Data Services Website and the NASA Sky Calendar

 

Mercury at Maximum Elongation

Today Mercury reaches maximum elongation, the furthest point it will reach from the Sun in the sky and the highest it will be above the sunrise for this morning apparition. The planet is easily visible as a bright, starlike object about 15° above the rising Sun as the twilight begins. Over the next couple weeks Mercury will slide back into the sunrise, heading for superior conjunction on February 16th.

Continue reading “Mercury at Maximum Elongation”

Apehelion

Today the Earth is furthest from the Sun, a point called apehelion. We will be about 152,098,232km (94,509,459miles) from the Sun. Compare this to the 147,098,290km (91,402,639miles) we were at perihelion on Jan 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 furthest for the middle of northern summer, 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.

2012 Solstices and Equinoxes
  UT HST
Perihelion Jan 5 03:59UT Jan 4 17:59HST
Spring Equinox Mar 20 05:14UT Mar 19 19:14HST
Summer Solstice Jun 20 23:09UT Jun 20 13:09HST
Apehelion Jul 4 23:59UT Jul 4 13:59HST
Fall Equinox Sep 22 14:49UT Sep 22 04:49HST
Winter Solstice Dec 21 11:12UT Dec 21 01:12HST
 
Source: USNO Data Services Website and the NASA Sky Calendar

 

Spring Equinox

Spring equinox occurs today at 19:14HST. Today there will be little difference between the length of the night compared to number of daylight hours. This is the first day of spring as marked by many cultures in the northern hemisphere.

Some calendars may mark the first day of spring on the 20th. And it is, for much of the world. For Hawai’i the equinox occurs on the 19th when you consider the time zone difference.

2012 Solstices and Equinoxes
  UT HST
Perihelion Jan 5 03:59UT Jan 4 17:59HST
Spring Equinox Mar 20 05:14UT Mar 19 19:14HST
Summer Solstice Jun 20 23:09UT Jun 20 13:09HST
Apehelion Jul 4 23:59UT Jul 4 13:59HST
Fall Equinox Sep 22 14:49UT Sep 22 04:49HST
Winter Solstice Dec 21 11:12UT Dec 21 01:12HST
 
Source: USNO Data Services Website and the NASA Sky Calendar

 

Mars Close Approach

Mars during the 2005 opposition
Mars during the 2005 opposition
Today 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.