19 June 2016

Summer Solstice 2016

The Summer Solstice is a special moment in the grand scheme of the Earth-Sun system, a date that represents a still-stand in the cycles that govern our universe. The solstice arrives on Monday 20th for the USA (Tuesday 21st for most of the rest of the world) when the north polar axis of Earth is tilted at its maximum toward the Sun. In addition to this being the longest day in the Northern Hemisphere for the entire year, there are other interesting effects.

The duration of the longest day in the Northern Hemisphere is a relative duration. In San Francisco, the length of the day on the Solstice is 14 hours 47 minutes, but that duration depends upon the latitude north of the Equator. The further north you are located, the longer the longest-day at Solstice. For example, in Seattle the Solstice day lasts 16 hours, and in Anchorage Alaska, the Solstice day lasts 19 hours 21 minutes, and in addition when you are that far north twilight never fully fades to dark and the sky remains in twilight glow the entire time the Sun is below the horizon. Of course, extreme situations emerge in locations such as the far northern reaches of Alaska, Canada, Greenland, Iceland, the Nordic Countries and Russia that lie above the Arctic Circle where the Sun is above the horizon for 24 hours on the day of the summer Solstice.

Solstice & Equinox
The term Solstice means 'Sun standing still' and refers to the perception from an Earth-bound point of view that the Sun appears to stand still in the sense of its gradual change in altitude on a daily basis. Of course, the Sun never stops moving from east to west each day, but the careful observer armed with a sundial would notice that the Sun, which has for six months been increasing in altitude at local noon each day, will appear to 'stand still' on the Solstice and gradually reverse course over the coming days, starting its six month downward trajectory toward Fall and Winter. The grand cycle of the Sun is of course attributed to the fact that the Earth is tilted on its axis and from a fixed spot on Earth, we perceive the Sun's changing altitude in a graceful cycle that slows and stops and reverses course each Solstice, and reaches a peak transition during the Equinoxes. The image shows this nicely.

This year's Solstice also features a Full Moon, so enjoy the shortest night with a bright and shiny Moon to accompany you.

This excellent article in Sky & Telescope provides further illumination on the subject.

Image courtesy Sky & Telescope.

27 May 2016

Mars at Opposition

Mars at Opposition
Mars just reached opposition, a time when it is in a straight line with the Earth and Sun. Mars therefore rises at sunset and is visible all night. It is also at its brightest, because usually opposition is also when the planet is at its closest approach to Earth and is fully illuminated, like a Full Moon.

Mars is presently located in Scorpius and as viewed from Earth is going through 'retrograde motion' in which the steady westward movement of the planet is temporarily interrupted by a reversal in motion back toward the east, as the Earth speeds past Mars in its orbit. The path of Mars in the background stars is nicely captured in this image from Naked Eye Planets and shows the retrograde path of Mars quite clearly.

Mars is easy to spot, a bright orange dot in the south that is grouped near another bright orange-red dot (in this case, Antares, the brightest star in Scorpius), and contrasting with a yellow-white dot that is Saturn.

Image courtesy Sky & Telescope

25 April 2016

Moon, Mars and Saturn

Mars, Moon and Saturn
Mars and Saturn are moving toward opposition (in May and June, respectively), which means they are going to be rising earlier and be more visible in the evening sky, and will be brightening over the weeks ahead. These planets are in Scorpius and Ophiuchus, low in the south in the latter part of the evening through the early morning hours.

The waning Moon passes through this region over the nights of 24-25-26 April and should be a nice picture mixed with orange Mars, yellow Saturn, and the red giant star Antares in Scorpius.

Hope you can spot these two gems and the Moon as they line up for a few days, making the sky that much more interesting to see.

Image courtesy of Sky & Telescope.

10 April 2016

Moon to Occult Aldebaran

Moon Occulting a Star
Astronomical alignments are special events, times when the motions of the Earth and the rest of the cosmos brings about a particularly interesting juxtaposition of objects in the sky. Today (Sunday 10 April) the waxing crescent Moon will align itself with the bright star Aldebaran, covering it completely for observers in various parts of North America. See this article from Sky & Telescope for a detailed overview of the cities and the exact timing for disappearance and reappearance of Aldebaran.

The Moon sweeps around the entire night sky and touches each constellation of the Zodiac every month, passing in front of hundreds of naked-eye visible stars during its journey. But it is very uncommon for the Moon to pass in front of the brightest stars in the night sky. Aldebaran is a 'first magnitude' star, one of only 22 stars that are at magnitude 1 or brighter (and only four of these are close enough to the Ecliptic to be ever occulted by the Moon: Aldebaran, Antares, Spica and Regulus)
. For that reason the covering and uncovering of a star like this is a dramatic event, worth taking a few minutes with binoculars or a telescope to watch the proper motion of the Moon as a vastly more distant star's light is interrupted by the surface on the edge of the Moon and the light twinkles and vanishes from view for an hour.

On the west coast, the event takes place in broad daylight, but that should not make it any less impressive. Disappearance is at 2:21 pm and reappearance at about 3:40 pm. Check the Sky & Telescope article for more precise timings from around North America.

22 March 2016

KFOG Broadcast: March 21, 2016.

The Morning Show at KFOG wanted the lowdown on the comet fly-bys, so we had a call and talked about the close approach, whether this was an 'extinction level' event, and whether you can see this wonder of the night. Listen here.

21 March 2016

A Comet Fly-By on March 22 is going to be a close one

Finding comet P/2016 BA14
Comet P/2016 BA14 will pass Earth at a near record-setting close distance on March 22. It will pass within 2.2 million miles (about 9 lunar distances), a reasonably wide miss but nonetheless a close shave in the grand scheme of cometary fly-bys. And at its estimated size of 1500 feet, it is plenty large to cause catastrophic damage to Earth. Luckily we have no risk and no danger, and we also have a great network of telescopes watching for such objects. We can spot them quite far in advance.

Comet P/2016 BA14 is not alone. There is a companion called 252P/Linear with it that will also pass close to Earth but will not be a threat. The two comets are likely from the same origin but split apart.

You'll need a telescope to see either one, but with a full Moon this week, it will take some work. The image shows where to look on March 21st at closest approach.

More information from Sky & Telescope and from Earth Sky.

19 March 2016

The Moon and Jupiter

Full Moon and Jupiter
Jupiter recently reached opposition, appearing at its brightest and traversing the night sky from sunset to sunrise. It's the most obvious beacon in the night sky, far outshining everything around it. That is, except for the Moon which of course is the brightest object in the night sky. This week as the Moon moves through its full phase, it has a close encounter with Jupiter on the evening of March 21.

By the way, since the Moon is full this week (on Wednesday March 23rd) just after the Spring Equinox, it will rise due East and set due West on that day, roughly mirroring the position of the Sun six months hence, on the Fall Equinox.

23 January 2016

KFOG Broadcast - January 20, 2016

I spent a few minutes with Irish Greg and No Name on the KFOG Morning Show talking about the view of all 5 'naked eye' planets in the morning sky this week. If you don't have good weather now, keep trying and at least 4 of the 5 will be visible over the coming weeks. Here's to clear skies! Click here to listen.