What's Up: July 1-8, Jared May

What’s Up This First Week of July

It looks like the forecast this week will disappoint most stargazers and astrophotographers – almost nothing but rainy partially cloudy nights. It’s possible there are stretches of time with low cloud coverage overhead after the sun has set. The temperature will swing through the 70s in the few hours following sunset. While these temperatures are very comfortable, warm temperatures may lead to turbulence in the air which can have negative effects on telescope viewing. During the sparse times of no overhead clouds be on the lookout for the full moon, Saturn, and a very bright Venus. You can’t necessarily observe this, but there was a big gravitational wave announcement last week!

The full moon will occur this Monday, July 3rd, so if you see the eastern sky starting to light up during sunset, that’s why. The full moon is bad news for people trying to observe a night sky full of faint starlight and deep-sky objects. 

Most people know that the moon causes the tides, but did you know that the moon is tidally locked with the Earth? That is why we always see the same side of the moon. Only space probes and the Apollo astronauts have seen the far side of the moon. Pictures of the far side show a surface peppered with craters – far more than the side facing us. That is because the moon acts as a gravitational shield for the Earth and pulls asteroids into it. The Earth also has a protective atmosphere that causes asteroids and meteors to burn up and break apart (this causes the classic “shooting star” appearance). Since the moon has effectively no atmosphere, nothing is stopping these asteroids from slamming right into the lunar surface at full speed.

The near (front) side of the moon at left, and the far (back) side at right. Notice the difference in the number of dark lunar “seas” between the two sides. (The seas are ancient lava fields).

If you hang around stargazing for long enough, you will see Saturn poke out above the eastern horizon at midnight. If you have an unobstructed eastern horizon, try viewing Saturn when it is really low to see the distortions of Earth’s atmosphere. The planet may appear redder, slightly misshaped, and may even appear to wobble around (this is due to turbulence in the atmosphere). The image on the left is how Saturn may appear far above the horizon and the image on the right shows how Saturn may appear low to the horizon.

Those with small telescopes can spot between five and eight of Saturn’s moons on good nights. Saturn rises after midnight at this time of the year

On Friday, July 7th, the waning gibbous moon will pass near this gas giant. A set of binoculars will be perfect for observing this meetup. A steady hand and careful eyes when observing Saturn through binoculars will reveal an elliptical shape which is the result of the massive ring system surrounding the planet. 

Also on Friday, July 7th, spot Venus setting in the western sky shortly after sunset. It may appear particularly bright and that’s because Venus (already the brightest object in the night sky beside the moon) will be at its greatest illuminated extent. While this inner planet will only be 25% illuminated (like a waxing crescent moon), it is at a point in its orbit that makes its face appear 37 arcseconds across which together make it appear slightly brighter than usual. 

Venus will be at its brightest this week.

In 2015 an experiment called LIGO (Laser Interferometer Gravitational-Wave Observatory) detected the “sound” of colliding supermassive black holes from a distant galaxy. Since then, it has heard many other black hole collisions. But it can “hear” these events because these very massive objects, as they move through space, emit gravitational waves. This is much like the ripples caused by throwing a rock into a pond. A more recent experiment called NANOGrav used a collection of radio telescopes to carefully measure pulsars, which are the collapsed cores of massive stars spinning faster than your kitchen blender. Pulsars spin at incredibly regular rates and so any distortion to the gravitational field around them causes their spin rate to slightly change. These tiny changes can be detected and by looking at several pulsars, astronomers and physicists successfully measured the gravitational wave background caused by orbiting blackholes throughout the universe. These groundbreaking results were announced last Thursday, June 29th and their publication can be found publicly here: https://arxiv.org/abs/2306.16213 .

Computer visualization of two black holes merging. These events can be detected by the LIGO instruments on Earth. The green represent invisible (but for their effect) waves of space itself.

Hopefully, the clouds are forgiving this week and part for at least a few hours after sunset to reveal a sky full of stars. When the night sky is revealed, lean back and enjoy the twinkling display of constellations, planets, and maybe a shooting star or two. During the breaks in the cloudy nights, be on the lookout for the full moon, Saturn low in the sky, and a brightness-boosted Venus. Don’t worry too much about gravitational waves – you won’t be able to feel them since they only distort space by much less than a trillionth of an inch.

As the astronomers say,

Clear Skies!