GB hurdler Tiffany Porter goes in this first semi-final. USA sprinter Brianna Rollins is the class of the field. 

Top two go through, plus the two overall fastest losers. 

Thomas Rohler - who has thrown over 90m this year - lands one at 79.47m first up.

Over 83m would qualify you automatically. 

The BBC big guns are out for tonight's athletics action. Tune into Gabby Logan, Michael Johnson, Denise Lewis et al on BBC One and online now.

How many of the Olympic sports have you done? Let us know. TWENTY-ONE?!

Jago: Yep taken part in 20, not done judo, equestrian, taekwondo, wrestling, pentathlon, fencing, gymnastics, handball, synchro, polo, triathlon.

Gil: I've tried 21 at very varying levels. 10 more to tick off at some stage!

LL Hughes: I can tick off 11 Olympic disciplines in "Olympic Bingo" if you count when I used to cycle to work for cycling

The first women's 100m hurdles semi is due away at 00:45 BST. Tiffany Porter of GB goes in it. 

We've got the athletics up shortly, but what else is going on right now? Take a look:

• Table tennis - China v Japan (Gold medal match)

• Taekwondo - Men's -58kg and Women's -49kg (finals)

Coming up: 

• 00:30: Handball - Croatia v Poland (Men's quarter-final)
• 02:00: Basketball - Croatia v Serbia (Men's quarter-final)
• 02:00: Women's Beach Volleyball - Brazil v USA (Bronze medal match)
• 02:15: Volleyball - Brazil v Argentina (men's quarter-finals)
• 04:00: Women's Beach Volleyball -Germany v Brazil (Gold medal match)

Tonight sees perhaps the most gladiatorial, most primal of the track and field events as the javelin arrives. The men's qualification has just begun.

For viewers of a certain age it will always summon up memories of a particularly chilling episode of '999' with Michael Buerk. Oooof....

Image source, Getty Images

No Brits in action tonight, not even Mick Hill, so keep an eye on German Thomas Rohler in qualifying. He has chucked it 91.28m this season.

That's four-and-a-half cricket pitches, end to end. Fetch that!

How many Olympic sports have you tried? We have an early leader with 12.

Jack Degge: I’ve tried 12. Athletics, Badminton, Basketball, Cycling, Football, Golf, Gymnastics, Rugby, Table Tennis, Tennis and more

Itsamadworld: Along with a few horses I once rode a a camel for 5 days, that'd make a cool Olympic Sport

Annie Doherty: Does going for the milk on a bike count as sport?

Of course it does. The Milk Cup

Image source, Getty Images

It's a big night in beach volleyball tonight with the women's tournament coming to its conclusion, and what a setting.

It's sure to be a great atmosphere as Brazil's Franca Larissa and Rocha Talita take on American duo Kerri Walsh-Jennings and April Ross for bronze at 02:00 BST.

Then it's the big one at 04:00 - midnight in Rio - as Brazil's defending champions Agatha and Barbara play Germany's Ludwig and Walkenhorst for the gold medal.

Image source, AP

In the basketball - one that I can tick off my list - the United States have cruised past Argentina 105-78 to move into the semi-finals.

Image source, Reuters

How many of the Olympic sports have you ever tried?

Mr Moon: Does pony trekking count as equestrian?

At this time of night, at this stage of the Games - I'm going to allow it. YES

Ilesanmi Timileyin: looking forward to Ese Brume winning Nigeria's first medal of these games

Ese Brume goes in the long jump final (from 01:15 BST)

There are 31 Olympic sports on the schedule.

But how many have you ever taken part in? At any level?

There must be some very sporty men and women out there. Can anyone claim 20?

I think I've done about six. And two since the age of 16...

Let me know your scores on the board - #bbcrio2016

Tom Fordyce
Chief sports writer in Rio

Hot and humid in the Estadio Olimpico, a big yellow moon overhead, smoky with the occasional drifting cloud. A skinny crowd thus far despite the presence later on, in the 200m semis, of The Bolter himself. Let's give it time.

Sam Holloway: This might be the first night for over a week where I go to bed before 2am. But... ooh, athletics. Shall I push on?

Vicky Mayman: No fatigue here, watching Olympics from NYC! Loving BBC updates we are only shown US and occasional Canadian athletes go #TeamGB, external

And there are also two British women in action in the long jump final (from 01:15 BST).

Shara Proctor - silver medallist at last year's world champs - didn't make it to the final but Jazmin Sawyers and Lorraine Ugen both did.

Can they challenge the medals?